COMPOSITION
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Types of Film Lights and their efficiency – CRI, Color Temperature and Luminous Efficacy
Read more: Types of Film Lights and their efficiency – CRI, Color Temperature and Luminous Efficacynofilmschool.com/types-of-film-lights
“Not every light performs the same way. Lights and lighting are tricky to handle. You have to plan for every circumstance. But the good news is, lighting can be adjusted. Let’s look at different factors that affect lighting in every scene you shoot. ”
Use CRI, Luminous Efficacy and color temperature controls to match your needs.
Color Temperature
Color temperature describes the “color” of white light by a light source radiated by a perfect black body at a given temperature measured in degrees Kelvinhttps://www.pixelsham.com/2019/10/18/color-temperature/
CRI
“The Color Rendering Index is a measurement of how faithfully a light source reveals the colors of whatever it illuminates, it describes the ability of a light source to reveal the color of an object, as compared to the color a natural light source would provide. The highest possible CRI is 100. A CRI of 100 generally refers to a perfect black body, like a tungsten light source or the sun. ”https://www.studiobinder.com/blog/what-is-color-rendering-index/
https://en.wikipedia.org/wiki/Color_rendering_index
Light source CCT (K) CRI Low-pressure sodium (LPS/SOX) 1800 −44 Clear mercury-vapor 6410 17 High-pressure sodium (HPS/SON) 2100 24 Coated mercury-vapor 3600 49 Halophosphate warm-white fluorescent 2940 51 Halophosphate cool-white fluorescent 4230 64 Tri-phosphor warm-white fluorescent 2940 73 Halophosphate cool-daylight fluorescent 6430 76 “White” SON 2700 82 Standard LED Lamp 2700–5000 83 Quartz metal halide 4200 85 Tri-phosphor cool-white fluorescent 4080 89 High-CRI LED lamp (blue LED) 2700–5000 95 Ceramic discharge metal-halide lamp 5400 96 Ultra-high-CRI LED lamp (violet LED) 2700–5000 99 Incandescent/halogen bulb 3200 100 Luminous Efficacy
Luminous efficacy is a measure of how well a light source produces visible light, watts out versus watts in, measured in lumens per watt. In other words it is a measurement that indicates the ability of a light source to emit visible light using a given amount of power. It is a ratio of the visible energy to the power that goes into the bulb.FILM LIGHT TYPES
Consumer light types
Tungsten Lights
Light interiors and match domestic places or office locations. Daylight.Advantages of Tungsten Lights
Almost perfect color rendition
Low cost
Does not use mercury like CFLs (fluorescent) or mercury vapor lights
Better color temperature than standard tungsten
Longer life than a conventional incandescent
Instant on to full brightness, no warm-up time, and it is dimmableDisadvantages of Tungsten Lights
Extremely hot
High power requirement
The lamp is sensitive to oils and cannot be touched
The bulb is capable of blowing and sending hot glass shards outward. A screen or layer of glass on the outside of the lamp can protect users.Hydrargyrum medium-arc iodide lights
HMI’s are used when high output is required. They are also used to recreate sun shining through windows or to fake additional sun while shooting exteriors. HMIs can light huge areas at once.Advantages of HMI lights
High light output
Higher efficiency
High color temperatureDisadvantages of HMI lights:
High cost
High power requirement
Dims only to about 50%
the color temperature increases with dimming
HMI bulbs will explode is dropped and release toxic chemicalsFluorescent
Fluorescent film lighting is achieved by laying multiple tubes next to each other, combining as many as you want for the desired brightness. The good news is you can choose your bulbs to either be warm or cool depending on the scenario you’re shooting. You want to get these bulbs close to the subject because they’re not great at opening up spaces. Fluorescent lighting is used to light interiors and is more compact and cooler than tungsten or HMI lighting.Advantages of Fluorescent lights
High efficiency
Low power requirement
Low cost
Long lamp life
Cool
Capable of soft even lighting over a large area
LightweightDisadvantages of Fluorescent lights
Flicker
High CRI
Domestic tubes have low CRI & poor color rendition.LED
LED’s are more and more common on film sets. You can use batteries to power them. That makes them portable and sleek – no messy cabled needed. You can rig your own panels of LED lights to fit any space necessary as well. LED’s can also power Fresnel style lamp heads such as the Arri L-series.Advantages of LED light
Soft, even lighting
Pure light without UV-artifacts
High efficiency
Low power consumption, can be battery powered
Excellent dimming by means of pulse width modulation control
Long lifespan
Environmentally friendly
Insensitive to shock
No risk of explosionDisadvantages of LED light
High cost.
LED’s are currently still expensive for their total light output
DESIGN
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Disco Diffusion V4.1 Google Colab, Dall-E, Starryai – creating images with AI
Read more: Disco Diffusion V4.1 Google Colab, Dall-E, Starryai – creating images with AIDisco Diffusion (DD) is a Google Colab Notebook which leverages an AI Image generating technique called CLIP-Guided Diffusion to allow you to create compelling and beautiful images from just text inputs. Created by Somnai, augmented by Gandamu, and building on the work of RiversHaveWings, nshepperd, and many others.
Phone app: https://www.starryai.com/
docs.google.com/document/d/1l8s7uS2dGqjztYSjPpzlmXLjl5PM3IGkRWI3IiCuK7g
colab.research.google.com/drive/1sHfRn5Y0YKYKi1k-ifUSBFRNJ8_1sa39
Colab, or “Colaboratory”, allows you to write and execute Python in your browser, with
– Zero configuration required
– Access to GPUs free of charge
– Easy sharing
https://80.lv/articles/a-beautiful-roman-villa-made-with-disco-diffusion-5-2/
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COLOR
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Björn Ottosson – OKlch color space
Read more: Björn Ottosson – OKlch color spaceBjörn Ottosson proposed OKlch in 2020 to create a color space that can closely mimic how color is perceived by the human eye, predicting perceived lightness, chroma, and hue.
The OK in OKLCH stands for Optimal Color.
- L: Lightness (the perceived brightness of the color)
- C: Chroma (the intensity or saturation of the color)
- H: Hue (the actual color, such as red, blue, green, etc.)
Also read:
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Is a MacBeth Colour Rendition Chart the Safest Way to Calibrate a Camera?
Read more: Is a MacBeth Colour Rendition Chart the Safest Way to Calibrate a Camera?www.colour-science.org/posts/the-colorchecker-considered-mostly-harmless/
“Unless you have all the relevant spectral measurements, a colour rendition chart should not be used to perform colour-correction of camera imagery but only for white balancing and relative exposure adjustments.”
“Using a colour rendition chart for colour-correction might dramatically increase error if the scene light source spectrum is different from the illuminant used to compute the colour rendition chart’s reference values.”
“other factors make using a colour rendition chart unsuitable for camera calibration:
– Uncontrolled geometry of the colour rendition chart with the incident illumination and the camera.
– Unknown sample reflectances and ageing as the colour of the samples vary with time.
– Low samples count.
– Camera noise and flare.
– Etc…“Those issues are well understood in the VFX industry, and when receiving plates, we almost exclusively use colour rendition charts to white balance and perform relative exposure adjustments, i.e. plate neutralisation.”
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Image rendering bit depth
Read more: Image rendering bit depthThe terms 8-bit, 16-bit, 16-bit float, and 32-bit refer to different data formats used to store and represent image information, as bits per pixel.
https://en.wikipedia.org/wiki/Color_depth
In color technology, color depth also known as bit depth, is either the number of bits used to indicate the color of a single pixel, OR the number of bits used for each color component of a single pixel.
When referring to a pixel, the concept can be defined as bits per pixel (bpp).
When referring to a color component, the concept can be defined as bits per component, bits per channel, bits per color (all three abbreviated bpc), and also bits per pixel component, bits per color channel or bits per sample (bps). Modern standards tend to use bits per component, but historical lower-depth systems used bits per pixel more often.
Color depth is only one aspect of color representation, expressing the precision with which the amount of each primary can be expressed; the other aspect is how broad a range of colors can be expressed (the gamut). The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a digital code value to a location in a color space.
Here’s a simple explanation of each.
8-bit images (i.e. 24 bits per pixel for a color image) are considered Low Dynamic Range.
They can store around 5 stops of light and each pixel carry a value from 0 (black) to 255 (white).
As a comparison, DSLR cameras can capture ~12-15 stops of light and they use RAW files to store the information.16-bit: This format is commonly referred to as “half-precision.” It uses 16 bits of data to represent color values for each pixel. With 16 bits, you can have 65,536 discrete levels of color, allowing for relatively high precision and smooth gradients. However, it has a limited dynamic range, meaning it cannot accurately represent extremely bright or dark values. It is commonly used for regular images and textures.
16-bit float: This format is an extension of the 16-bit format but uses floating-point numbers instead of fixed integers. Floating-point numbers allow for more precise calculations and a larger dynamic range. In this case, the 16 bits are used to store both the color value and the exponent, which controls the range of values that can be represented. The 16-bit float format provides better accuracy and a wider dynamic range than regular 16-bit, making it useful for high-dynamic-range imaging (HDRI) and computations that require more precision.
32-bit: (i.e. 96 bits per pixel for a color image) are considered High Dynamic Range. This format, also known as “full-precision” or “float,” uses 32 bits to represent color values and offers the highest precision and dynamic range among the three options. With 32 bits, you have a significantly larger number of discrete levels, allowing for extremely accurate color representation, smooth gradients, and a wide range of brightness values. It is commonly used for professional rendering, visual effects, and scientific applications where maximum precision is required.
Bits and HDR coverage
High Dynamic Range (HDR) images are designed to capture a wide range of luminance values, from the darkest shadows to the brightest highlights, in order to reproduce a scene with more accuracy and detail. The bit depth of an image refers to the number of bits used to represent each pixel’s color information. When comparing 32-bit float and 16-bit float HDR images, the drop in accuracy primarily relates to the precision of the color information.
A 32-bit float HDR image offers a higher level of precision compared to a 16-bit float HDR image. In a 32-bit float format, each color channel (red, green, and blue) is represented by 32 bits, allowing for a larger range of values to be stored. This increased precision enables the image to retain more details and subtleties in color and luminance.
On the other hand, a 16-bit float HDR image utilizes 16 bits per color channel, resulting in a reduced range of values that can be represented. This lower precision leads to a loss of fine details and color nuances, especially in highly contrasted areas of the image where there are significant differences in luminance.
The drop in accuracy between 32-bit and 16-bit float HDR images becomes more noticeable as the exposure range of the scene increases. Exposure range refers to the span between the darkest and brightest areas of an image. In scenes with a limited exposure range, where the luminance differences are relatively small, the loss of accuracy may not be as prominent or perceptible. These images usually are around 8-10 exposure levels.
However, in scenes with a wide exposure range, such as a landscape with deep shadows and bright highlights, the reduced precision of a 16-bit float HDR image can result in visible artifacts like color banding, posterization, and loss of detail in both shadows and highlights. The image may exhibit abrupt transitions between tones or colors, which can appear unnatural and less realistic.
To provide a rough estimate, it is often observed that exposure values beyond approximately ±6 to ±8 stops from the middle gray (18% reflectance) may be more prone to accuracy issues in a 16-bit float format. This range may vary depending on the specific implementation and encoding scheme used.
To summarize, the drop in accuracy between 32-bit and 16-bit float HDR images is mainly related to the reduced precision of color information. This decrease in precision becomes more apparent in scenes with a wide exposure range, affecting the representation of fine details and leading to visible artifacts in the image.
In practice, this means that exposure values beyond a certain range will experience a loss of accuracy and detail when stored in a 16-bit float format. The exact range at which this loss occurs depends on the encoding scheme and the specific implementation. However, in general, extremely bright or extremely dark values that fall outside the representable range may be subject to quantization errors, resulting in loss of detail, banding, or other artifacts.
HDRs used for lighting purposes are usually slightly convolved to improve on sampling speed and removing specular artefacts. To that extent, 16 bit float HDRIs tend to me most used in CG cycles.
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Composition – cinematography Cheat Sheet
Read more: Composition – cinematography Cheat Sheet
Where is our eye attracted first? Why?
Size. Focus. Lighting. Color.
Size. Mr. White (Harvey Keitel) on the right.
Focus. He’s one of the two objects in focus.
Lighting. Mr. White is large and in focus and Mr. Pink (Steve Buscemi) is highlighted by
a shaft of light.
Color. Both are black and white but the read on Mr. White’s shirt now really stands out.
What type of lighting?-> High key lighting.
Features bright, even illumination and few conspicuous shadows. This lighting key is often used in musicals and comedies.Low key lighting
Features diffused shadows and atmospheric pools of light. This lighting key is often used in mysteries and thrillers.High contrast lighting
Features harsh shafts of lights and dramatic streaks of blackness. This type of lighting is often used in tragedies and melodramas.What type of shot?
Extreme long shot
Taken from a great distance, showing much of the locale. Ifpeople are included in these shots, they usually appear as mere specks-> Long shot
Corresponds to the space between the audience and the stage in a live theater. The long shots show the characters and some of the locale.Full shot
Range with just enough space to contain the human body in full. The full shot shows the character and a minimal amount of the locale.Medium shot
Shows the human figure from the knees or waist up.Close-Up
Concentrates on a relatively small object and show very little if any locale.Extreme close-up
Focuses on an unnaturally small portion of an object, giving that part great detail and symbolic significance.What angle?
Bird’s-eye view.
The shot is photographed directly from above. This type of shot can be disorienting, and the people photographed seem insignificant.High angle.
This angle reduces the size of the objects photographed. A person photographed from this angle seems harmless and insignificant, but to a lesser extent than with the bird’s-eye view.-> Eye-level shot.
The clearest view of an object, but seldom intrinsically dramatic, because it tends to be the norm.Low angle.
This angle increases high and a sense of verticality, heightening the importance of the object photographed. A person shot from this angle is given a sense of power and respect.Oblique angle.
For this angle, the camera is tilted laterally, giving the image a slanted appearance. Oblique angles suggest tension, transition, a impending movement. They are also called canted or dutch angles.What is the dominant color?
The use of color in this shot is symbolic. The scene is set in warehouse. Both the set and characters are blues, blacks and whites.
This was intentional allowing for the scenes and shots with blood to have a great level of contrast.
What is the Lens/Filter/Stock?
Telephoto lens.
A lens that draws objects closer but also diminishes the illusion of depth.Wide-angle lens.
A lens that takes in a broad area and increases the illusion of depth but sometimes distorts the edges of the image.Fast film stock.
Highly sensitive to light, it can register an image with little illumination. However, the final product tends to be grainy.Slow film stock.
Relatively insensitive to light, it requires a great deal of illumination. The final product tends to look polished.The lens is not wide-angle because there isn’t a great sense of depth, nor are several planes in focus. The lens is probably long but not necessarily a telephoto lens because the depth isn’t inordinately compressed.
The stock is fast because of the grainy quality of the image.
Subsidiary Contrast; where does the eye go next?
The two guns.
How much visual information is packed into the image? Is the texture stark, moderate, or highly detailed?
Minimalist clutter in the warehouse allows a focus on a character driven thriller.
What is the Composition?
Horizontal.
Compositions based on horizontal lines seem visually at rest and suggest placidity or peacefulness.Vertical.
Compositions based on vertical lines seem visually at rest and suggest strength.-> Diagonal.
Compositions based on diagonal, or oblique, lines seem dynamic and suggest tension or anxiety.-> Binary. Binary structures emphasize parallelism.
Triangle.
Triadic compositions stress the dynamic interplay among three mainCircle.
Circular compositions suggest security and enclosure.Is the form open or closed? Does the image suggest a window that arbitrarily isolates a fragment of the scene? Or a proscenium arch, in which the visual elements are carefully arranged and held in balance?
The most nebulous of all the categories of mise en scene, the type of form is determined by how consciously structured the mise en scene is. Open forms stress apparently simple techniques, because with these unself-conscious methods the filmmaker is able to emphasize the immediate, the familiar, the intimate aspects of reality. In open-form images, the frame tends to be deemphasized. In closed form images, all the necessary information is carefully structured within the confines of the frame. Space seems enclosed and self-contained rather than continuous.
Could argue this is a proscenium arch because this is such a classic shot with parallels and juxtapositions.
Is the framing tight or loose? Do the character have no room to move around, or can they move freely without impediments?
Shots where the characters are placed at the edges of the frame and have little room to move around within the frame are considered tight.
Longer shots, in which characters have room to move around within the frame, are considered loose and tend to suggest freedom.
Center-framed giving us the entire scene showing isolation, place and struggle.
Depth of Field. On how many planes is the image composed (how many are in focus)? Does the background or foreground comment in any way on the mid-ground?
Standard DOF, one background and clearly defined foreground.
Which way do the characters look vis-a-vis the camera?
An actor can be photographed in any of five basic positions, each conveying different psychological overtones.
Full-front (facing the camera):
the position with the most intimacy. The character is looking in our direction, inviting our complicity.Quarter Turn:
the favored position of most filmmakers. This position offers a high degree of intimacy but with less emotional involvement than the full-front.-> Profile (looking of the frame left or right):
More remote than the quarter turn, the character in profile seems unaware of being observed, lost in his or her own thoughts.Three-quarter Turn:
More anonymous than the profile, this position is useful for conveying a character’s unfriendly or antisocial feelings, for in effect, the character is partially turning his or her back on us, rejecting our interest.Back to Camera:
The most anonymous of all positions, this position is often used to suggest a character’s alienation from the world. When a character has his or her back to the camera, we can only guess what’s taking place internally, conveying a sense of concealment, or mystery.How much space is there between the characters?
Extremely close, for a gunfight.
The way people use space can be divided into four proxemic patterns.
Intimate distances.
The intimate distance ranges from skin contact to about eighteen inches away. This is the distance of physical involvement–of love, comfort, and tenderness between individuals.-> Personal distances.
The personal distance ranges roughly from eighteen inches away to about four feet away. These distances tend to be reserved for friends and acquaintances. Personal distances preserve the privacy between individuals, yet these rages don’t necessarily suggest exclusion, as intimate distances often do.Social distances.
The social distance rages from four feet to about twelve feet. These distances are usually reserved for impersonal business and casual social gatherings. It’s a friendly range in most cases, yet somewhat more formal than the personal distance.Public distances.
The public distance extends from twelve feet to twenty-five feet or more. This range tends to be formal and rather detached. -
VES Cinematic Color – Motion-Picture Color Management
Read more: VES Cinematic Color – Motion-Picture Color ManagementThis paper presents an introduction to the color pipelines behind modern feature-film visual-effects and animation.
Authored by Jeremy Selan, and reviewed by the members of the VES Technology Committee including Rob Bredow, Dan Candela, Nick Cannon, Paul Debevec, Ray Feeney, Andy Hendrickson, Gautham Krishnamurti, Sam Richards, Jordan Soles, and Sebastian Sylwan.
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Colormaxxing – What if I told you that rgb(255, 0, 0) is not actually the reddest red you can have in your browser?
Read more: Colormaxxing – What if I told you that rgb(255, 0, 0) is not actually the reddest red you can have in your browser?https://karuna.dev/colormaxxing
https://webkit.org/blog-files/color-gamut/comparison.html
https://oklch.com/#70,0.1,197,100
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Photography basics: Color Temperature and White Balance
Read more: Photography basics: Color Temperature and White Balance
Color Temperature of a light source describes the spectrum of light which is radiated from a theoretical “blackbody” (an ideal physical body that absorbs all radiation and incident light – neither reflecting it nor allowing it to pass through) with a given surface temperature.
https://en.wikipedia.org/wiki/Color_temperature
Or. Most simply it is a method of describing the color characteristics of light through a numerical value that corresponds to the color emitted by a light source, measured in degrees of Kelvin (K) on a scale from 1,000 to 10,000.
More accurately. The color temperature of a light source is the temperature of an ideal backbody that radiates light of comparable hue to that of the light source.
As such, the color temperature of a light source is a numerical measurement of its color appearance. It is based on the principle that any object will emit light if it is heated to a high enough temperature, and that the color of that light will shift in a predictable manner as the temperature is increased. The system is based on the color changes of a theoretical “blackbody radiator” as it is heated from a cold black to a white hot state.
So, why do we measure the hue of the light as a “temperature”? This was started in the late 1800s, when the British physicist William Kelvin heated a block of carbon. It glowed in the heat, producing a range of different colors at different temperatures. The black cube first produced a dim red light, increasing to a brighter yellow as the temperature went up, and eventually produced a bright blue-white glow at the highest temperatures. In his honor, Color Temperatures are measured in degrees Kelvin, which are a variation on Centigrade degrees. Instead of starting at the temperature water freezes, the Kelvin scale starts at “absolute zero,” which is -273 Centigrade.
More about black bodies here: https://www.pixelsham.com/2013/03/14/black-body-color
Details in the post
LIGHTING
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Composition and The Expressive Nature Of Light
Read more: Composition and The Expressive Nature Of Lighthttp://www.huffingtonpost.com/bill-danskin/post_12457_b_10777222.html
George Sand once said “ The artist vocation is to send light into the human heart.”
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HDRI shooting and editing by Xuan Prada and Greg Zaal
Read more: HDRI shooting and editing by Xuan Prada and Greg Zaalwww.xuanprada.com/blog/2014/11/3/hdri-shooting
http://blog.gregzaal.com/2016/03/16/make-your-own-hdri/
http://blog.hdrihaven.com/how-to-create-high-quality-hdri/
Shooting checklist
- Full coverage of the scene (fish-eye shots)
- Backplates for look-development (including ground or floor)
- Macbeth chart for white balance
- Grey ball for lighting calibration
- Chrome ball for lighting orientation
- Basic scene measurements
- Material samples
- Individual HDR artificial lighting sources if required
Methodology
- Plant the tripod where the action happens, stabilise it and level it
- Set manual focus
- Set white balance
- Set ISO
- Set raw+jpg
- Set apperture
- Metering exposure
- Set neutral exposure
- Read histogram and adjust neutral exposure if necessary
- Shot slate (operator name, location, date, time, project code name, etc)
- Set auto bracketing
- Shot 5 to 7 exposures with 3 stops difference covering the whole environment
- Place the aromatic kit where the tripod was placed, and take 3 exposures. Keep half of the grey sphere hit by the sun and half in shade.
- Place the Macbeth chart 1m away from tripod on the floor and take 3 exposures
- Take backplates and ground/floor texture references
- Shoot reference materials
- Write down measurements of the scene, specially if you are shooting interiors.
- If shooting artificial lights take HDR samples of each individual lighting source.
Exposures starting point
- Day light sun visible ISO 100 F22
- Day light sun hidden ISO 100 F16
- Cloudy ISO 320 F16
- Sunrise/Sunset ISO 100 F11
- Interior well lit ISO 320 F16
- Interior ambient bright ISO 320 F10
- Interior bad light ISO 640 F10
- Interior ambient dark ISO 640 F8
- Low light situation ISO 640 F5
NOTE: The goal is to clean the initial individual brackets before or at merging time as much as possible.
This means:- keeping original shooting metadata
- de-fringing
- removing aberration (through camera lens data or automatically)
- at 32 bit
- in ACEScg (or ACES) wherever possible
Here are the tips for using the chromatic ball in VFX projects, written in English:
https://www.linkedin.com/posts/bellrodrigo_here-are-the-tips-for-using-the-chromatic-activity-7200950595438940160-AGBpTips for Using the Chromatic Ball in VFX Projects**
The chromatic ball is an invaluable tool in VFX work, helping to capture lighting and reflection data crucial for integrating CGI elements seamlessly. Here are some tips to maximize its effectiveness:
1. **Positioning**:
– Place the chromatic ball in the same lighting conditions as the main subject. Ensure it is visible in the camera frame but not obstructing the main action.
– Ideally, place the ball where the CGI elements will be integrated to match the lighting and reflections accurately.2. **Recording Reference Footage**:
– Capture reference footage of the chromatic ball at the beginning and end of each scene or lighting setup. This ensures you have consistent lighting data for the entire shoot.3. **Consistent Angles**:
– Use consistent camera angles and heights when recording the chromatic ball. This helps in comparing and matching lighting setups across different shots.4. **Combine with a Gray Ball**:
– Use a gray ball alongside the chromatic ball. The gray ball provides a neutral reference for exposure and color balance, complementing the chromatic ball’s reflection data.5. **Marking Positions**:
– Mark the position of the chromatic ball on the set to ensure consistency when shooting multiple takes or different camera angles.6. **Lighting Analysis**:
– Analyze the chromatic ball footage to understand the light sources, intensity, direction, and color temperature. This information is crucial for creating realistic CGI lighting and shadows.7. **Reflection Analysis**:
– Use the chromatic ball to capture the environment’s reflections. This helps in accurately reflecting the CGI elements within the same scene, making them blend seamlessly.8. **Use HDRI**:
– Capture High Dynamic Range Imagery (HDRI) of the chromatic ball. HDRI provides detailed lighting information and can be used to light CGI scenes with greater realism.9. **Communication with VFX Team**:
– Ensure that the VFX team is aware of the chromatic ball’s data and how it was captured. Clear communication ensures that the data is used effectively in post-production.10. **Post-Production Adjustments**:
– In post-production, use the chromatic ball data to adjust the CGI elements’ lighting and reflections. This ensures that the final output is visually cohesive and realistic. -
Open Source Nvidia Omniverse
Read more: Open Source Nvidia Omniverseblogs.nvidia.com/blog/2019/03/18/omniverse-collaboration-platform/
developer.nvidia.com/nvidia-omniverse
An open, Interactive 3D Design Collaboration Platform for Multi-Tool Workflows to simplify studio workflows for real-time graphics.
It supports Pixar’s Universal Scene Description technology for exchanging information about modeling, shading, animation, lighting, visual effects and rendering across multiple applications.
It also supports NVIDIA’s Material Definition Language, which allows artists to exchange information about surface materials across multiple tools.
With Omniverse, artists can see live updates made by other artists working in different applications. They can also see changes reflected in multiple tools at the same time.
For example an artist using Maya with a portal to Omniverse can collaborate with another artist using UE4 and both will see live updates of each others’ changes in their application.
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Black Body color aka the Planckian Locus curve for white point eye perception
Read more: Black Body color aka the Planckian Locus curve for white point eye perceptionhttp://en.wikipedia.org/wiki/Black-body_radiation
Black-body radiation is the type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
A black-body at room temperature appears black, as most of the energy it radiates is infra-red and cannot be perceived by the human eye. At higher temperatures, black bodies glow with increasing intensity and colors that range from dull red to blindingly brilliant blue-white as the temperature increases.
The Black Body Ultraviolet Catastrophe Experiment
In photography, color temperature describes the spectrum of light which is radiated from a “blackbody” with that surface temperature. A blackbody is an object which absorbs all incident light — neither reflecting it nor allowing it to pass through.
The Sun closely approximates a black-body radiator. Another rough analogue of blackbody radiation in our day to day experience might be in heating a metal or stone: these are said to become “red hot” when they attain one temperature, and then “white hot” for even higher temperatures. Similarly, black bodies at different temperatures also have varying color temperatures of “white light.”
Despite its name, light which may appear white does not necessarily contain an even distribution of colors across the visible spectrum.
Although planets and stars are neither in thermal equilibrium with their surroundings nor perfect black bodies, black-body radiation is used as a first approximation for the energy they emit. Black holes are near-perfect black bodies, and it is believed that they emit black-body radiation (called Hawking radiation), with a temperature that depends on the mass of the hole.
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Photography basics: Lumens vs Candelas (candle) vs Lux vs FootCandle vs Watts vs Irradiance vs Illuminance
Read more: Photography basics: Lumens vs Candelas (candle) vs Lux vs FootCandle vs Watts vs Irradiance vs Illuminancehttps://www.translatorscafe.com/unit-converter/en-US/illumination/1-11/
The power output of a light source is measured using the unit of watts W. This is a direct measure to calculate how much power the light is going to drain from your socket and it is not relatable to the light brightness itself.
The amount of energy emitted from it per second. That energy comes out in a form of photons which we can crudely represent with rays of light coming out of the source. The higher the power the more rays emitted from the source in a unit of time.
Not all energy emitted is visible to the human eye, so we often rely on photometric measurements, which takes in account the sensitivity of human eye to different wavelenghts
Details in the post
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Types of Film Lights and their efficiency – CRI, Color Temperature and Luminous Efficacy
Read more: Types of Film Lights and their efficiency – CRI, Color Temperature and Luminous Efficacynofilmschool.com/types-of-film-lights
“Not every light performs the same way. Lights and lighting are tricky to handle. You have to plan for every circumstance. But the good news is, lighting can be adjusted. Let’s look at different factors that affect lighting in every scene you shoot. ”
Use CRI, Luminous Efficacy and color temperature controls to match your needs.
Color Temperature
Color temperature describes the “color” of white light by a light source radiated by a perfect black body at a given temperature measured in degrees Kelvinhttps://www.pixelsham.com/2019/10/18/color-temperature/
CRI
“The Color Rendering Index is a measurement of how faithfully a light source reveals the colors of whatever it illuminates, it describes the ability of a light source to reveal the color of an object, as compared to the color a natural light source would provide. The highest possible CRI is 100. A CRI of 100 generally refers to a perfect black body, like a tungsten light source or the sun. ”https://www.studiobinder.com/blog/what-is-color-rendering-index/
https://en.wikipedia.org/wiki/Color_rendering_index
Light source CCT (K) CRI Low-pressure sodium (LPS/SOX) 1800 −44 Clear mercury-vapor 6410 17 High-pressure sodium (HPS/SON) 2100 24 Coated mercury-vapor 3600 49 Halophosphate warm-white fluorescent 2940 51 Halophosphate cool-white fluorescent 4230 64 Tri-phosphor warm-white fluorescent 2940 73 Halophosphate cool-daylight fluorescent 6430 76 “White” SON 2700 82 Standard LED Lamp 2700–5000 83 Quartz metal halide 4200 85 Tri-phosphor cool-white fluorescent 4080 89 High-CRI LED lamp (blue LED) 2700–5000 95 Ceramic discharge metal-halide lamp 5400 96 Ultra-high-CRI LED lamp (violet LED) 2700–5000 99 Incandescent/halogen bulb 3200 100 Luminous Efficacy
Luminous efficacy is a measure of how well a light source produces visible light, watts out versus watts in, measured in lumens per watt. In other words it is a measurement that indicates the ability of a light source to emit visible light using a given amount of power. It is a ratio of the visible energy to the power that goes into the bulb.FILM LIGHT TYPES
Consumer light types
Tungsten Lights
Light interiors and match domestic places or office locations. Daylight.Advantages of Tungsten Lights
Almost perfect color rendition
Low cost
Does not use mercury like CFLs (fluorescent) or mercury vapor lights
Better color temperature than standard tungsten
Longer life than a conventional incandescent
Instant on to full brightness, no warm-up time, and it is dimmableDisadvantages of Tungsten Lights
Extremely hot
High power requirement
The lamp is sensitive to oils and cannot be touched
The bulb is capable of blowing and sending hot glass shards outward. A screen or layer of glass on the outside of the lamp can protect users.Hydrargyrum medium-arc iodide lights
HMI’s are used when high output is required. They are also used to recreate sun shining through windows or to fake additional sun while shooting exteriors. HMIs can light huge areas at once.Advantages of HMI lights
High light output
Higher efficiency
High color temperatureDisadvantages of HMI lights:
High cost
High power requirement
Dims only to about 50%
the color temperature increases with dimming
HMI bulbs will explode is dropped and release toxic chemicalsFluorescent
Fluorescent film lighting is achieved by laying multiple tubes next to each other, combining as many as you want for the desired brightness. The good news is you can choose your bulbs to either be warm or cool depending on the scenario you’re shooting. You want to get these bulbs close to the subject because they’re not great at opening up spaces. Fluorescent lighting is used to light interiors and is more compact and cooler than tungsten or HMI lighting.Advantages of Fluorescent lights
High efficiency
Low power requirement
Low cost
Long lamp life
Cool
Capable of soft even lighting over a large area
LightweightDisadvantages of Fluorescent lights
Flicker
High CRI
Domestic tubes have low CRI & poor color rendition.LED
LED’s are more and more common on film sets. You can use batteries to power them. That makes them portable and sleek – no messy cabled needed. You can rig your own panels of LED lights to fit any space necessary as well. LED’s can also power Fresnel style lamp heads such as the Arri L-series.Advantages of LED light
Soft, even lighting
Pure light without UV-artifacts
High efficiency
Low power consumption, can be battery powered
Excellent dimming by means of pulse width modulation control
Long lifespan
Environmentally friendly
Insensitive to shock
No risk of explosionDisadvantages of LED light
High cost.
LED’s are currently still expensive for their total light output -
Photography basics: Exposure Value vs Photographic Exposure vs Il/Luminance vs Pixel luminance measurements
Read more: Photography basics: Exposure Value vs Photographic Exposure vs Il/Luminance vs Pixel luminance measurementsAlso see: https://www.pixelsham.com/2015/05/16/how-aperture-shutter-speed-and-iso-affect-your-photos/
In photography, exposure value (EV) is a number that represents a combination of a camera’s shutter speed and f-number, such that all combinations that yield the same exposure have the same EV (for any fixed scene luminance).
The EV concept was developed in an attempt to simplify choosing among combinations of equivalent camera settings. Although all camera settings with the same EV nominally give the same exposure, they do not necessarily give the same picture. EV is also used to indicate an interval on the photographic exposure scale. 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop
EV 0 corresponds to an exposure time of 1 sec and a relative aperture of f/1.0. If the EV is known, it can be used to select combinations of exposure time and f-number.
Note EV does not equal to photographic exposure. Photographic Exposure is defined as how much light hits the camera’s sensor. It depends on the camera settings mainly aperture and shutter speed. Exposure value (known as EV) is a number that represents the exposure setting of the camera.
Thus, strictly, EV is not a measure of luminance (indirect or reflected exposure) or illuminance (incidental exposure); rather, an EV corresponds to a luminance (or illuminance) for which a camera with a given ISO speed would use the indicated EV to obtain the nominally correct exposure. Nonetheless, it is common practice among photographic equipment manufacturers to express luminance in EV for ISO 100 speed, as when specifying metering range or autofocus sensitivity.
The exposure depends on two things: how much light gets through the lenses to the camera’s sensor and for how long the sensor is exposed. The former is a function of the aperture value while the latter is a function of the shutter speed. Exposure value is a number that represents this potential amount of light that could hit the sensor. It is important to understand that exposure value is a measure of how exposed the sensor is to light and not a measure of how much light actually hits the sensor. The exposure value is independent of how lit the scene is. For example a pair of aperture value and shutter speed represents the same exposure value both if the camera is used during a very bright day or during a dark night.
Each exposure value number represents all the possible shutter and aperture settings that result in the same exposure. Although the exposure value is the same for different combinations of aperture values and shutter speeds the resulting photo can be very different (the aperture controls the depth of field while shutter speed controls how much motion is captured).
EV 0.0 is defined as the exposure when setting the aperture to f-number 1.0 and the shutter speed to 1 second. All other exposure values are relative to that number. Exposure values are on a base two logarithmic scale. This means that every single step of EV – plus or minus 1 – represents the exposure (actual light that hits the sensor) being halved or doubled.
https://www.streetdirectory.com/travel_guide/141307/photography/exposure_value_ev_and_exposure_compensation.html
Formula
https://en.wikipedia.org/wiki/Exposure_value
https://www.scantips.com/lights/math.html
which means 2EV = N² / t
where
- N is the relative aperture (f-number) Important: Note that f/stop values must first be squared in most calculations
- t is the exposure time (shutter speed) in seconds
EV 0 corresponds to an exposure time of 1 sec and an aperture of f/1.0.
Example: If f/16 and 1/4 second, then this is:
(N² / t) = (16 × 16 ÷ 1/4) = (16 × 16 × 4) = 1024.
Log₂(1024) is EV 10. Meaning, 210 = 1024.
Collecting photographic exposure using Light Meters
The exposure meter in the camera does not know whether the subject itself is bright or not. It simply measures the amount of light that comes in, and makes a guess based on that. The camera will aim for 18% gray, meaning if you take a photo of an entirely white surface, and an entirely black surface you should get two identical images which both are gray (at least in theory)
https://en.wikipedia.org/wiki/Light_meter
For reflected-light meters, camera settings are related to ISO speed and subject luminance by the reflected-light exposure equation:
where
- N is the relative aperture (f-number)
- t is the exposure time (“shutter speed”) in seconds
- L is the average scene luminance
- S is the ISO arithmetic speed
- K is the reflected-light meter calibration constant
For incident-light meters, camera settings are related to ISO speed and subject illuminance by the incident-light exposure equation:
where
- E is the illuminance (in lux)
- C is the incident-light meter calibration constant
Two values for K are in common use: 12.5 (Canon, Nikon, and Sekonic) and 14 (Minolta, Kenko, and Pentax); the difference between the two values is approximately 1/6 EV.
For C a value of 250 is commonly used.Nonetheless, it is common practice among photographic equipment manufacturers to also express luminance in EV for ISO 100 speed. Using K = 12.5, the relationship between EV at ISO 100 and luminance L is then :
L = 2(EV-3)
The situation with incident-light meters is more complicated than that for reflected-light meters, because the calibration constant C depends on the sensor type. Illuminance is measured with a flat sensor; a typical value for C is 250 with illuminance in lux. Using C = 250, the relationship between EV at ISO 100 and illuminance E is then :
E = 2.5 * 2(EV)
https://nofilmschool.com/2018/03/want-easier-and-faster-way-calculate-exposure-formula
Three basic factors go into the exposure formula itself instead: aperture, shutter, and ISO. Plus a light meter calibration constant.
f-stop²/shutter (in seconds) = lux * ISO/C
If you at least know four of those variables, you’ll be able to calculate the missing value.
So, say you want to figure out how much light you’re going to need in order to shoot at a certain f-stop. Well, all you do is plug in your values (you should know the f-stop, ISO, and your light meter calibration constant) into the formula below:
lux = C (f-stop²/shutter (in seconds))/ISO
Exposure Value Calculator:
https://snapheadshots.com/resources/exposure-and-light-calculator
https://www.scantips.com/lights/exposurecalc.html
https://www.pointsinfocus.com/tools/exposure-settings-ev-calculator/#google_vignette
From that perspective, an exposure stop is a measurement of Exposure and provides a universal linear scale to measure the increase and decrease in light, exposed to the image sensor, due to changes in shutter speed, iso & f-stop.
+-1 stop is a doubling or halving of the amount of light let in when taking a photo.
1 EV is just another way to say one stop of exposure change.One major use of EV (Exposure Value) is just to measure any change of exposure, where one EV implies a change of one stop of exposure. Like when we compensate our picture in the camera.
If the picture comes out too dark, our manual exposure could correct the next one by directly adjusting one of the three exposure controls (f/stop, shutter speed, or ISO). Or if using camera automation, the camera meter is controlling it, but we might apply +1 EV exposure compensation (or +1 EV flash compensation) to make the result goal brighter, as desired. This use of 1 EV is just another way to say one stop of exposure change.
On a perfect day the difference from sampling the sky vs the sun exposure with diffusing spot meters is about 3.2 exposure difference.
~15.4 EV for the sun ~12.2 EV for the sky
That is as a ballpark. All still influenced by surroundings, accuracy parameters, fov of the sensor…
EV calculator
https://www.scantips.com/lights/evchart.html#calc
http://www.fredparker.com/ultexp1.htm
Exposure value is basically used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step, also commonly referred to as a “stop”.
https://contrastly.com/a-guide-to-understanding-exposure-value-ev/
Retrieving photographic exposure from an image
All you can hope to measure with your camera and some images is the relative reflected luminance. Even if you have the camera settings. https://en.wikipedia.org/wiki/Relative_luminance
If you REALLY want to know the amount of light in absolute radiometric units, you’re going to need to use some kind of absolute light meter or measured light source to calibrate your camera. For references on how to do this, see: Section 2.5 Obtaining Absolute Radiance from http://www.pauldebevec.com/Research/HDR/debevec-siggraph97.pdf
IF you are still trying to gauge relative brightness, the level of the sun in Nuke can vary, but it should be in the thousands. Ie: between 30,000 and 65,0000 rgb value depending on time of the day, season and atmospherics.
The values for a 12 o’clock sun, with the sun sampled at EV 15.5 (shutter 1/30, ISO 100, F22) is 32.000 RGB max values (or 32,000 pixel luminance).
The thing to keep an eye for is the level of contrast between sunny side/fill side. The terminator should be quite obvious, there can be up to 3 stops difference between fill/key in sunny lit objects.Note: In Foundry’s Nuke, the software will map 18% gray to whatever your center f/stop is set to in the viewer settings (f/8 by default… change that to EV by following the instructions below).
You can experiment with this by attaching an Exposure node to a Constant set to 0.18, setting your viewer read-out to Spotmeter, and adjusting the stops in the node up and down. You will see that a full stop up or down will give you the respective next value on the aperture scale (f8, f11, f16 etc.).
One stop doubles or halves the amount or light that hits the filmback/ccd, so everything works in powers of 2.
So starting with 0.18 in your constant, you will see that raising it by a stop will give you .36 as a floating point number (in linear space), while your f/stop will be f/11 and so on.If you set your center stop to 0 (see below) you will get a relative readout in EVs, where EV 0 again equals 18% constant gray.
Note: make sure to set your Nuke read node to ‘raw data’
In other words. Setting the center f-stop to 0 means that in a neutral plate, the middle gray in the macbeth chart will equal to exposure value 0. EV 0 corresponds to an exposure time of 1 sec and an aperture of f/1.0.
To switch Foundry’s Nuke’s SpotMeter to return the EV of an image, click on the main viewport, and then press s, this opens the viewer’s properties. Now set the center f-stop to 0 in there. And the SpotMeter in the viewport will change from aperture and fstops to EV.
If you are trying to gauge the EV from the pixel luminance in the image:
– Setting the center f-stop to 0 means that in a neutral plate, the middle 18% gray will equal to exposure value 0.
– So if EV 0 = 0.18 middle gray in nuke which equal to a pixel luminance of 0.18, doubling that value, doubles the EV..18 pixel luminance = 0EV .36 pixel luminance = 1EV .72 pixel luminance = 2EV 1.46 pixel luminance = 3EV ...
This is a Geometric Progression function: xn = ar(n-1)
The most basic example of this function is 1,2,4,8,16,32,… The sequence starts at 1 and doubles each time, so
- a=1 (the first term)
- r=2 (the “common ratio” between terms is a doubling)
And we get:
{a, ar, ar2, ar3, … }
= {1, 1×2, 1×22, 1×23, … }
= {1, 2, 4, 8, … }
In this example the function translates to: n = 2(n-1)
You can graph this curve through this expression: x = 2(y-1) :
You can go back and forth between the two values through a geometric progression function and a log function:
(Note: in a spreadsheet this is: = POWER(2; cell# -1) and =LOG(cell#, 2)+1) )
2(y-1) log2(x)+1 x y 1 1 2 2 4 3 8 4 16 5 32 6 64 7 128 8 256 9 512 10 1024 11 2048 12 4096 13 Translating this into a geometric progression between an image pixel luminance and EV:
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