renderwonk.com/publications/s2010-shading-course/snow/sigg2010_physhadcourse_ILM.pdf
Local files:
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Free HDRI libraries
noahwitchell.com
http://www.noahwitchell.com/freebieslocationtextures.com
https://locationtextures.com/panoramas/maxroz.com
https://www.maxroz.com/hdri/listHDRI Haven
https://hdrihaven.com/Poly Haven
https://polyhaven.com/hdrisDomeble
https://www.domeble.com/IHDRI
https://www.ihdri.com/HDRMaps
https://hdrmaps.com/NoEmotionHdrs.net
http://noemotionhdrs.net/hdrday.htmlOpenFootage.net
https://www.openfootage.net/hdri-panorama/HDRI-hub
https://www.hdri-hub.com/hdrishop/hdri.zwischendrin
https://www.zwischendrin.com/en/browse/hdriLonger list here:
https://cgtricks.com/list-sites-free-hdri/
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HDRI Median Cut plugin
www.hdrlabs.com/picturenaut/plugins.html
Note. The Median Cut algorithm is typically used for color quantization, which involves reducing the number of colors in an image while preserving its visual quality. It doesn’t directly provide a way to identify the brightest areas in an image. However, if you’re interested in identifying the brightest areas, you might want to look into other methods like thresholding, histogram analysis, or edge detection, through openCV for example.
Here is an openCV example:
# bottom left coordinates = 0,0 import numpy as np import cv2 # Load the HDR or EXR image image = cv2.imread('your_image_path.exr', cv2.IMREAD_UNCHANGED) # Load as-is without modification # Calculate the luminance from the HDR channels (assuming RGB format) luminance = np.dot(image[..., :3], [0.299, 0.587, 0.114]) # Set a threshold value based on estimated EV threshold_value = 2.4 # Estimated threshold value based on 4.8 EV # Apply the threshold to identify bright areas # Theluminancearray contains the calculated luminance values for each pixel in the image. # Thethreshold_valueis a user-defined value that represents a cutoff point, separating "bright" and "dark" areas in terms of perceived luminance.thresholded = (luminance > threshold_value) * 255 # Convert the thresholded image to uint8 for contour detection thresholded = thresholded.astype(np.uint8) # Find contours of the bright areas contours, _ = cv2.findContours(thresholded, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE) # Create a list to store the bounding boxes of bright areas bright_areas = [] # Iterate through contours and extract bounding boxes for contour in contours: x, y, w, h = cv2.boundingRect(contour) # Adjust y-coordinate based on bottom-left origin y_bottom_left_origin = image.shape[0] - (y + h) bright_areas.append((x, y_bottom_left_origin, x + w, y_bottom_left_origin + h)) # Store as (x1, y1, x2, y2) # Print the identified bright areas print("Bright Areas (x1, y1, x2, y2):") for area in bright_areas: print(area)More details
Luminance and Exposure in an EXR Image:
- An EXR (Extended Dynamic Range) image format is often used to store high dynamic range (HDR) images that contain a wide range of luminance values, capturing both dark and bright areas.
- Luminance refers to the perceived brightness of a pixel in an image. In an RGB image, luminance is often calculated using a weighted sum of the red, green, and blue channels, where different weights are assigned to each channel to account for human perception.
- In an EXR image, the pixel values can represent radiometrically accurate scene values, including actual radiance or irradiance levels. These values are directly related to the amount of light emitted or reflected by objects in the scene.
The luminance line is calculating the luminance of each pixel in the image using a weighted sum of the red, green, and blue channels. The three float values [0.299, 0.587, 0.114] are the weights used to perform this calculation.
These weights are based on the concept of luminosity, which aims to approximate the perceived brightness of a color by taking into account the human eye’s sensitivity to different colors. The values are often derived from the NTSC (National Television System Committee) standard, which is used in various color image processing operations.
Here’s the breakdown of the float values:
- 0.299: Weight for the red channel.
- 0.587: Weight for the green channel.
- 0.114: Weight for the blue channel.
The weighted sum of these channels helps create a grayscale image where the pixel values represent the perceived brightness. This technique is often used when converting a color image to grayscale or when calculating luminance for certain operations, as it takes into account the human eye’s sensitivity to different colors.
For the threshold, remember that the exact relationship between EV values and pixel values can depend on the tone-mapping or normalization applied to the HDR image, as well as the dynamic range of the image itself.
To establish a relationship between exposure and the threshold value, you can consider the relationship between linear and logarithmic scales:
- Linear and Logarithmic Scales:
- Exposure values in an EXR image are often represented in logarithmic scales, such as EV (exposure value). Each increment in EV represents a doubling or halving of the amount of light captured.
- Threshold values for luminance thresholding are usually linear, representing an actual luminance level.
- Conversion Between Scales:
- To establish a mathematical relationship, you need to convert between the logarithmic exposure scale and the linear threshold scale.
- One common method is to use a power function. For instance, you can use a power function to convert EV to a linear intensity value.
threshold_value = base_value * (2 ** EV)
Here,
EVis the exposure value,base_valueis a scaling factor that determines the relationship between EV and threshold_value, and2 ** EVis used to convert the logarithmic EV to a linear intensity value. - Choosing the Base Value:
- The
base_valuefactor should be determined based on the dynamic range of your EXR image and the specific luminance values you are dealing with. - You may need to experiment with different values of
base_valueto achieve the desired separation of bright areas from the rest of the image.
- The
Let’s say you have an EXR image with a dynamic range of 12 EV, which is a common range for many high dynamic range images. In this case, you want to set a threshold value that corresponds to a certain number of EV above the middle gray level (which is often considered to be around 0.18).
Here’s an example of how you might determine a
base_valueto achieve this:# Define the dynamic range of the image in EV dynamic_range = 12 # Choose the desired number of EV above middle gray for thresholding desired_ev_above_middle_gray = 2 # Calculate the threshold value based on the desired EV above middle gray threshold_value = 0.18 * (2 ** (desired_ev_above_middle_gray / dynamic_range)) print("Threshold Value:", threshold_value) -
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Capturing the world in HDR for real time projects – Call of Duty: Advanced Warfare
Real-World Measurements for Call of Duty: Advanced Warfare
www.activision.com/cdn/research/Real_World_Measurements_for_Call_of_Duty_Advanced_Warfare.pdf
Local version
Real_World_Measurements_for_Call_of_Duty_Advanced_Warfare.pdf
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domeble – Hi-Resolution CGI Backplates and 360° HDRI
When collecting hdri make sure the data supports basic metadata, such as:
- Iso
- Aperture
- Exposure time or shutter time
- Color temperature
- Color space Exposure value (what the sensor receives of the sun intensity in lux)
- 7+ brackets (with 5 or 6 being the perceived balanced exposure)
In image processing, computer graphics, and photography, high dynamic range imaging (HDRI or just HDR) is a set of techniques that allow a greater dynamic range of luminances (a Photometry measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle) between the lightest and darkest areas of an image than standard digital imaging techniques or photographic methods. This wider dynamic range allows HDR images to represent more accurately the wide range of intensity levels found in real scenes ranging from direct sunlight to faint starlight and to the deepest shadows.
The two main sources of HDR imagery are computer renderings and merging of multiple photographs, which in turn are known as low dynamic range (LDR) or standard dynamic range (SDR) images. Tone Mapping (Look-up) techniques, which reduce overall contrast to facilitate display of HDR images on devices with lower dynamic range, can be applied to produce images with preserved or exaggerated local contrast for artistic effect. Photography
In photography, dynamic range is measured in Exposure Values (in photography, exposure value denotes all combinations of camera shutter speed and relative aperture that give the same exposure. The concept was developed in Germany in the 1950s) differences or stops, between the brightest and darkest parts of the image that show detail. An increase of one EV or one stop is a doubling of the amount of light.
The human response to brightness is well approximated by a Steven’s power law, which over a reasonable range is close to logarithmic, as described by the Weber�Fechner law, which is one reason that logarithmic measures of light intensity are often used as well.
HDR is short for High Dynamic Range. It’s a term used to describe an image which contains a greater exposure range than the “black” to “white” that 8 or 16-bit integer formats (JPEG, TIFF, PNG) can describe. Whereas these Low Dynamic Range images (LDR) can hold perhaps 8 to 10 f-stops of image information, HDR images can describe beyond 30 stops and stored in 32 bit images.
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HDR and Color
https://www.soundandvision.com/content/nits-and-bits-hdr-and-color
In HD we often refer to the range of available colors as a color gamut. Such a color gamut is typically plotted on a two-dimensional diagram, called a CIE chart, as shown in at the top of this blog. Each color is characterized by its x/y coordinates.
Good enough for government work, perhaps. But for HDR, with its higher luminance levels and wider color, the gamut becomes three-dimensional.
For HDR the color gamut therefore becomes a characteristic we now call the color volume. It isn’t easy to show color volume on a two-dimensional medium like the printed page or a computer screen, but one method is shown below. As the luminance becomes higher, the picture eventually turns to white. As it becomes darker, it fades to black. The traditional color gamut shown on the CIE chart is simply a slice through this color volume at a selected luminance level, such as 50%.
Three different color volumes—we still refer to them as color gamuts though their third dimension is important—are currently the most significant. The first is BT.709 (sometimes referred to as Rec.709), the color gamut used for pre-UHD/HDR formats, including standard HD.
The largest is known as BT.2020; it encompasses (roughly) the range of colors visible to the human eye (though ET might find it insufficient!).
Between these two is the color gamut used in digital cinema, known as DCI-P3.
sRGB
D65
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Thank you for visiting!! Please bear with us while we go through a redesign of the blog. New features and phone support on the way!
Akiyoshi Kitaoka – Surround biased illumination perception
https://x.com/AkiyoshiKitaoka/status/1798705648001327209
The left face appears whitish and the right one blackish, but they are made up of the same luminance.
https://community.wolfram.com/groups/-/m/t/3191015
Illusory staircase Gelb effect
https://www.psy.ritsumei.ac.jp/akitaoka/illgelbe.html
Riot ‘Arcane’ – the Priciest Animated Series Ever
Sources familiar with details of the production pegged the cost of the first nine 40-minute episodes at north of $80 million; the second batch of nine about to air has a price tag approaching $100 million. What drove the cost far beyond typical animation expenses, insiders say, were both a labor-intensive approach and frequent cost overruns triggered by delayed script deliveries after the second season was put into production with only a fraction of the season written.
But even more eyebrow-raising than the production cost was that Riot spent $60 million of its own money to promote the first season of “Arcane,” exponentially more than a studio would typically spend for a show it isn’t distributing — and far more than Netflix itself spent ($4 million per episode). Reps for the streaming service declined to comment for this article.
Artificial Analysis Mochi 1 – an open source text 2 video model
Mochi 1 AI operates on a pay-as-you-go model, meaning you only pay for the services you utilize without any hidden fees.
Bella – Fast Spectral Rendering
Bella works in spectral space, allowing effects such as BSDF wavelength dependency, diffraction, or atmosphere to be modeled far more accurately than in color space.
https://superrendersfarm.com/blog/uncategorized/bella-a-new-spectral-physically-based-renderer/
Scans Factory – Unreal 5.4 demo – Rome Walkthrough
PlanCraft – An assumptions based project schedule generator
https://www.hasielhassan.com/PlanCraft/#about
It helps you create and Open Schedule Format (OSF) JSON file for your projects.
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FEATURED COMPOSITION POSTS
Composition and The Expressive Nature Of Light
http://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.” …
FEATURED LIGHTING
Christopher Butler – Understanding the Eye-Mind Connection – Vision is a mental process
https://www.chrbutler.com/understanding-the-eye-mind-connection The intricate relationship between the eyes and the brain, often termed the eye-mind connection, reveals that vision is predominantly …
GretagMacbeth Color Checker Numeric Values and Middle Gray
The human eye perceives half scene brightness not as the linear 50% of the present energy (linear nature values) but …
Magnific.ai Relight – change the entire lighting of a scene
It’s a new Magnific spell that allows you to change the entire lighting of a scene and, optionally, the background …
Sun cone angle (angular diameter) as perceived by earth viewers
Also see: https://www.pixelsham.com/2020/08/01/solid-angle-measures/ The cone angle of the sun refers to the angular diameter of the sun as observed from …
Victor Perez – Sensitometry for VFX Artists | FMX 2023
ColorTransformationAnalysis.nk local copy ColorTransformationAnalysis.nk … -
Romain Chauliac – LightIt a lighting script for Maya and Arnold
LightIt is a script for Maya and Arnold that will help you and improve your lighting workflow.
Thanks to preset studio lighting components (lights, backdrop…), high quality studio scenes and HDRI library manager.
https://www.artstation.com/artwork/393emJ
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Image rendering bit depth
The terms 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.
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RICOH THETA Z1 51GB camera – 360° images in RAW format
https://theta360.com/en/about/theta/z1.html
- 23MP(6720 x 3360, 7K)
- superior noise reduction performance
- F2.1, F3.5 and F5.6
- 4K videos (3840 x 1920, 29.97fps)
- RAW (DNG) image format
- 360° live streaming in 4K
- record sound from 4 different directions when shooting video
- editing of 360° images in Adobe Photoshop Lightroom Classic CC
- Android™ base system for the OS. Use plug-ins to customize your own THETA.
- Wireless 2.4 GHz: 1 to 11ch or 1 to 13ch
- Wireless 5 GHz: W52 (36 to 48ch, channel bandwidth 20/40/80 MHz supported)
Theta Z1 is Ricoh’s flagship 360 camera that features 1-inch sensors, which are the largest available for dual lens 360 cameras. It has been a highly regarded camera among 360 photographers because of its excellent image quality, color accuracy, and its ability to shoot Raw DNG photos with exceptional exposure latitude.
Bracketing mode 2022
Rquirement: Basic app iOS ver.2.20.0, Android ver.2.5.0, Camera firmware ver.2.10.3
https://community.theta360.guide/t/new-feature-ae-bracket-added-in-the-shooting-mode-z1-only/8247
HDRi for VFX
https://community.theta360.guide/t/create-high-quality-hdri-for-vfx-using-ricoh-theta-z1/4789/4
ND filtering
https://community.theta360.guide/t/neutral-density-solution-for-most-theta-cameras/7331
https://community.theta360.guide/t/long-exposure-nd-filter-for-ricoh-theta/1100
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LUX vs LUMEN vs NITS vs CANDELA – What is the difference
More details here: Lumens vs Candelas (candle) vs Lux vs FootCandle vs Watts vs Irradiance vs Illuminance
https://www.inhouseav.com.au/blog/beginners-guide-nits-lumens-brightness/
Candela
Candela is the basic unit of measure of the entire volume of light intensity from any point in a single direction from a light source. Note the detail: it measures the total volume of light within a certain beam angle and direction.
While the luminance of starlight is around 0.001 cd/m2, that of a sunlit scene is around 100,000 cd/m2, which is a hundred millions times higher. The luminance of the sun itself is approximately 1,000,000,000 cd/m2.NIT
https://en.wikipedia.org/wiki/Candela_per_square_metre
The candela per square metre (symbol: cd/m2) is the unit of luminance in the International System of Units (SI). The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area. The nit (symbol: nt) is a non-SI name also used for this unit (1 nt = 1 cd/m2).[1] The term nit is believed to come from the Latin word nitēre, “to shine”. As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a display device.
NIT and cd/m2 (candela power) represent the same thing and can be used interchangeably. One nit is equivalent to one candela per square meter, where the candela is the amount of light which has been emitted by a common tallow candle, but NIT is not part of the International System of Units (abbreviated SI, from Systeme International, in French).
It’s easiest to think of a TV as emitting light directly, in much the same way as the Sun does. Nits are simply the measurement of the level of light (luminance) in a given area which the emitting source sends to your eyes or a camera sensor.
The Nit can be considered a unit of visible-light intensity which is often used to specify the brightness level of an LCD.
1 Nit is approximately equal to 3.426 Lumens. To work out a comparable number of Nits to Lumens, you need to multiply the number of Nits by 3.426. If you know the number of Lumens, and wish to know the Nits, simply divide the number of Lumens by 3.426.
Most consumer desktop LCDs have Nits of 200 to 300, the average TV most likely has an output capability of between 100 and 200 Nits, and an HDR TV ranges from 400 to 1,500 Nits.
Virtual Production sets currently sport around 6000 NIT ceiling and 1000 NIT wall panels.The ambient brightness of a sunny day with clear blue skies is between 7000-10,000 nits (between 3000-7000 nits for overcast skies and indirect sunlight).
A bright sunny day can have specular highlights that reach over 100,000 nits. Direct sunlight is around 1,600,000,000 nits.
10,000 nits is also the typical brightness of a fluorescent tube – bright, but not painful to look at.
https://www.displaydaily.com/article/display-daily/dolby-vision-vs-hdr10-clarified
Tests showed that a “black level” of 0.005 nits (cd/m²) satisfied the vast majority of viewers. While 0.005 nits is very close to true black, Griffis says Dolby can go down to a black of 0.0001 nits, even though there is no need or ability for displays to get that dark today.
How bright is white? Dolby says the range of 0.005 nits – 10,000 nits satisfied 84% of the viewers in their viewing tests.
The brightest consumer HDR displays today are about 1,500 nits. Professional displays where HDR content is color-graded can achieve up to 4,000 nits peak brightness.High brightness that would be in danger of damaging the eye would be in the neighborhood of 250,000 nits.
Lumens
Lumen is a measure of how much light is emitted (luminance, luminous flux) by an object. It indicates the total potential amount of light from a light source that is visible to the human eye.
Lumen is commonly used in the context of light bulbs or video-projectors as a metric for their brightness power.Lumen is used to describe light output, and about video projectors, it is commonly referred to as ANSI Lumens. Simply put, lumens is how to find out how bright a LED display is. The higher the lumens, the brighter to display!
Technically speaking, a Lumen is the SI unit of luminous flux, which is equal to the amount of light which is emitted per second in a unit solid angle of one steradian from a uniform source of one-candela intensity radiating in all directions.
LUX
Lux (lx) or often Illuminance, is a photometric unit along a given area, which takes in account the sensitivity of human eye to different wavelenghts. It is the measure of light at a specific distance within a specific area at that distance. Often used to measure the incidental sun’s intensity.
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StudioBinder.com – Photography basics: What is Dynamic Range in Photography
https://www.studiobinder.com/blog/what-is-dynamic-range-photography/
https://www.hdrsoft.com/resources/dri.html#bit-depth
The dynamic range is a ratio between the maximum and minimum values of a physical measurement. Its definition depends on what the dynamic range refers to.
For a scene: Dynamic range is the ratio between the brightest and darkest parts of the scene.
For a camera: Dynamic range is the ratio of saturation to noise. More specifically, the ratio of the intensity that just saturates the camera to the intensity that just lifts the camera response one standard deviation above camera noise.
For a display: Dynamic range is the ratio between the maximum and minimum intensities emitted from the screen.
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Types of Film Lights and their efficiency – CRI, Color Temperature and Luminous Efficacy
nofilmschool.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 -
Outpost VFX lighting tips
www.outpost-vfx.com/en/news/18-pro-tips-and-tricks-for-lighting
Get as much information regarding your plate lighting as possible
- Always use a reference
- Replicate what is happening in real life
- Invest into a solid HDRI
- Start Simple
- Observe real world lighting, photography and cinematography
- Don’t neglect the theory
- Learn the difference between realism and photo-realism.
- Keep your scenes organised
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Advanced Computer Vision with Python OpenCV and Mediapipe
https://www.freecodecamp.org/news/advanced-computer-vision-with-python/
https://www.freecodecamp.org/news/how-to-use-opencv-and-python-for-computer-vision-and-ai/
Working for a VFX (Visual Effects) studio provides numerous opportunities to leverage the power of Python and OpenCV for various tasks. OpenCV is a versatile computer vision library that can be applied to many aspects of the VFX pipeline. Here’s a detailed list of opportunities to take advantage of Python and OpenCV in a VFX studio:
- Image and Video Processing:
- Preprocessing: Python and OpenCV can be used for tasks like resizing, color correction, noise reduction, and frame interpolation to prepare images and videos for further processing.
- Format Conversion: Convert between different image and video formats using OpenCV’s capabilities.
- Tracking and Matchmoving:
- Feature Detection and Tracking: Utilize OpenCV to detect and track features in image sequences, which is essential for matchmoving tasks to integrate computer-generated elements into live-action footage.
- Rotoscoping and Masking:
- Segmentation and Masking: Use OpenCV for creating and manipulating masks and alpha channels for various VFX tasks, like isolating objects or characters from their backgrounds.
- Camera Calibration:
- Intrinsic and Extrinsic Calibration: Python and OpenCV can help calibrate cameras for accurate 3D scene reconstruction and camera tracking.
- 3D Scene Reconstruction:
- Stereoscopy: Use OpenCV to process stereoscopic image pairs for creating 3D depth maps and generating realistic 3D scenes.
- Structure from Motion (SfM): Implement SfM techniques to create 3D models from 2D image sequences.
- Green Screen and Blue Screen Keying:
- Chroma Keying: Implement advanced keying algorithms using OpenCV to seamlessly integrate actors and objects into virtual environments.
- Particle and Fluid Simulations:
- Particle Tracking: Utilize OpenCV to track and manipulate particles in fluid simulations for more realistic visual effects.
- Motion Analysis:
- Optical Flow: Implement optical flow algorithms to analyze motion patterns in footage, useful for creating dynamic VFX elements that follow the motion of objects.
- Virtual Set Extension:
- Camera Projection: Use camera calibration techniques to project virtual environments onto physical sets, extending the visual scope of a scene.
- Color Grading:
- Color Correction: Implement custom color grading algorithms to match the color tones and moods of different shots.
- Automated QC (Quality Control):
- Artifact Detection: Develop Python scripts to automatically detect and flag visual artifacts like noise, flicker, or compression artifacts in rendered frames.
- Data Analysis and Visualization:
- Performance Metrics: Use Python to analyze rendering times and optimize the rendering process.
- Data Visualization: Generate graphs and charts to visualize render farm usage, project progress, and resource allocation.
- Automating Repetitive Tasks:
- Batch Processing: Automate repetitive tasks like resizing images, applying filters, or converting file formats across multiple shots.
- Machine Learning Integration:
- Object Detection: Integrate machine learning models (using frameworks like TensorFlow or PyTorch) to detect and track specific objects or elements within scenes.
- Pipeline Integration:
- Custom Tools: Develop Python scripts and tools to integrate OpenCV-based processes seamlessly into the studio’s pipeline.
- Real-time Visualization:
- Live Previsualization: Implement real-time OpenCV-based visualizations to aid decision-making during the preproduction stage.
- VR and AR Integration:
- Augmented Reality: Use Python and OpenCV to integrate virtual elements into real-world footage, creating compelling AR experiences.
- Camera Effects:
- Lens Distortion: Correct lens distortions and apply various camera effects using OpenCV, contributing to the desired visual style.
Interpolating frames from an EXR sequence using OpenCV can be useful when you have only every second frame of a final render and you want to create smoother motion by generating intermediate frames. However, keep in mind that interpolating frames might not always yield perfect results, especially if there are complex changes between frames. Here’s a basic example of how you might use OpenCV to achieve this:
import cv2 import numpy as np import os # Replace with the path to your EXR frames exr_folder = "path_to_exr_frames" # Replace with the appropriate frame extension and naming convention frame_template = "frame_{:04d}.exr" # Define the range of frame numbers you have start_frame = 1 end_frame = 100 step = 2 # Define the output folder for interpolated frames output_folder = "output_interpolated_frames" os.makedirs(output_folder, exist_ok=True) # Loop through the frame range and interpolate for frame_num in range(start_frame, end_frame + 1, step): frame_path = os.path.join(exr_folder, frame_template.format(frame_num)) next_frame_path = os.path.join(exr_folder, frame_template.format(frame_num + step)) if os.path.exists(frame_path) and os.path.exists(next_frame_path): frame = cv2.imread(frame_path, cv2.IMREAD_ANYDEPTH | cv2.IMREAD_COLOR) next_frame = cv2.imread(next_frame_path, cv2.IMREAD_ANYDEPTH | cv2.IMREAD_COLOR) # Interpolate frames using simple averaging interpolated_frame = (frame + next_frame) / 2 # Save interpolated frame output_path = os.path.join(output_folder, frame_template.format(frame_num)) cv2.imwrite(output_path, interpolated_frame) print(f"Interpolated frame {frame_num}") # alternatively: print("Interpolated frame {}".format(frame_num))Please note the following points:
- The above example uses simple averaging to interpolate frames. More advanced interpolation methods might provide better results, such as motion-based algorithms like optical flow-based interpolation.
- EXR files can store high dynamic range (HDR) data, so make sure to use cv2.IMREAD_ANYDEPTH flag when reading these files.
- OpenCV might not support EXR format directly. You might need to use a library like exr to read and manipulate EXR files, and then convert them to OpenCV-compatible formats.
- Consider the characteristics of your specific render when using interpolation. If there are large changes between frames, the interpolation might lead to artifacts.
- Experiment with different interpolation methods and parameters to achieve the desired result.
- For a more advanced and accurate interpolation, you might need to implement or use existing algorithms that take into account motion estimation and compensation.
- Image and Video Processing:
-
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