COLOR

LIGHTING

  • What’s the Difference Between Ray Casting, Ray Tracing, Path Tracing and Rasterization? Physical light tracing…

    RASTERIZATION
    Rasterisation (or rasterization)
    is the task of taking the information described in a vector graphics format OR the vertices of triangles making 3D shapes and converting them into a raster image (a series of pixels, dots or lines, which, when displayed together, create the image which was represented via shapes), or in other words “rasterizing” vectors or 3D models onto a 2D plane for display on a computer screen.

    For each triangle of a 3D shape, you project the corners of the triangle on the virtual screen with some math (projective geometry). Then you have the position of the 3 corners of the triangle on the pixel screen. Those 3 points have texture coordinates, so you know where in the texture are the 3 corners. The cost is proportional to the number of triangles, and is only a little bit affected by the screen resolution.

    In computer graphics, a raster graphics or bitmap image is a dot matrix data structure that represents a generally rectangular grid of pixels (points of color), viewable via a monitor, paper, or other display medium.

    With rasterization, objects on the screen are created from a mesh of virtual triangles, or polygons, that create 3D models of objects. A lot of information is associated with each vertex, including its position in space, as well as information about color, texture and its “normal,” which is used to determine the way the surface of an object is facing.

    Computers then convert the triangles of the 3D models into pixels, or dots, on a 2D screen. Each pixel can be assigned an initial color value from the data stored in the triangle vertices.

    Further pixel processing or “shading,” including changing pixel color based on how lights in the scene hit the pixel, and applying one or more textures to the pixel, combine to generate the final color applied to a pixel.

     

    The main advantage of rasterization is its speed. However, rasterization is simply the process of computing the mapping from scene geometry to pixels and does not prescribe a particular way to compute the color of those pixels. So it cannot take shading, especially the physical light, into account and it cannot promise to get a photorealistic output. That’s a big limitation of rasterization.

    There are also multiple problems:


    • If you have two triangles one is behind the other, you will draw twice all the pixels. you only keep the pixel from the triangle that is closer to you (Z-buffer), but you still do the work twice.



    • The borders of your triangles are jagged as it is hard to know if a pixel is in the triangle or out. You can do some smoothing on those, that is anti-aliasing.



    • You have to handle every triangles (including the ones behind you) and then see that they do not touch the screen at all. (we have techniques to mitigate this where we only look at triangles that are in the field of view)



    • Transparency is hard to handle (you can’t just do an average of the color of overlapping transparent triangles, you have to do it in the right order)


     

     

     

    RAY CASTING
    It is almost the exact reverse of rasterization: you start from the virtual screen instead of the vector or 3D shapes, and you project a ray, starting from each pixel of the screen, until it intersect with a triangle.

    The cost is directly correlated to the number of pixels in the screen and you need a really cheap way of finding the first triangle that intersect a ray. In the end, it is more expensive than rasterization but it will, by design, ignore the triangles that are out of the field of view.

    You can use it to continue after the first triangle it hit, to take a little bit of the color of the next one, etc… This is useful to handle the border of the triangle cleanly (less jagged) and to handle transparency correctly.

     

    RAYTRACING


    Same idea as ray casting except once you hit a triangle you reflect on it and go into a different direction. The number of reflection you allow is the “depth” of your ray tracing. The color of the pixel can be calculated, based off the light source and all the polygons it had to reflect off of to get to that screen pixel.

    The easiest way to think of ray tracing is to look around you, right now. The objects you’re seeing are illuminated by beams of light. Now turn that around and follow the path of those beams backwards from your eye to the objects that light interacts with. That’s ray tracing.

    Ray tracing is eye-oriented process that needs walking through each pixel looking for what object should be shown there, which is also can be described as a technique that follows a beam of light (in pixels) from a set point and simulates how it reacts when it encounters objects.

    Compared with rasterization, ray tracing is hard to be implemented in real time, since even one ray can be traced and processed without much trouble, but after one ray bounces off an object, it can turn into 10 rays, and those 10 can turn into 100, 1000…The increase is exponential, and the the calculation for all these rays will be time consuming.

    Historically, computer hardware hasn’t been fast enough to use these techniques in real time, such as in video games. Moviemakers can take as long as they like to render a single frame, so they do it offline in render farms. Video games have only a fraction of a second. As a result, most real-time graphics rely on the another technique called rasterization.

     

     

    PATH TRACING
    Path tracing can be used to solve more complex lighting situations.

    Path tracing is a type of ray tracing. When using path tracing for rendering, the rays only produce a single ray per bounce. The rays do not follow a defined line per bounce (to a light, for example), but rather shoot off in a random direction. The path tracing algorithm then takes a random sampling of all of the rays to create the final image. This results in sampling a variety of different types of lighting.

    When a ray hits a surface it doesn’t trace a path to every light source, instead it bounces the ray off the surface and keeps bouncing it until it hits a light source or exhausts some bounce limit.
    It then calculates the amount of light transferred all the way to the pixel, including any color information gathered from surfaces along the way.
    It then averages out the values calculated from all the paths that were traced into the scene to get the final pixel color value.

    It requires a ton of computing power and if you don’t send out enough rays per pixel or don’t trace the paths far enough into the scene then you end up with a very spotty image as many pixels fail to find any light sources from their rays. So when you increase the the samples per pixel, you can see the image quality becomes better and better.

    Ray tracing tends to be more efficient than path tracing. Basically, the render time of a ray tracer depends on the number of polygons in the scene. The more polygons you have, the longer it will take.
    Meanwhile, the rendering time of a path tracer can be indifferent to the number of polygons, but it is related to light situation: If you add a light, transparency, translucence, or other shader effects, the path tracer will slow down considerably.

     
     

     

    Sources:
    https://medium.com/@junyingw/future-of-gaming-rasterization-vs-ray-tracing-vs-path-tracing-32b334510f1f

     

     

    blogs.nvidia.com/blog/2018/03/19/whats-difference-between-ray-tracing-rasterization/

     

    https://en.wikipedia.org/wiki/Rasterisation

     

     

    https://www.quora.com/Whats-the-difference-between-ray-tracing-and-path-tracing

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    Read more: What’s the Difference Between Ray Casting, Ray Tracing, Path Tracing and Rasterization? Physical light tracing…
  • Composition – cinematography Cheat Sheet

    https://moodle.gllm.ac.uk/pluginfile.php/190622/mod_resource/content/1/Cinematography%20Cheat%20Sheet.pdf

    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 main

    Circle.
    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.

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    Read more: Composition – cinematography Cheat Sheet
  • Practical Aspects of Spectral Data and LEDs in Digital Content Production and Virtual Production – SIGGRAPH 2022

     

    Comparison to the commercial side

     

    https://www.ecolorled.com/blog/detail/what-is-rgb-rgbw-rgbic-strip-lights

     

    RGBW (RGB + White) LED strip uses a 4-in-1 LED chip made up of red, green, blue, and white.

     

    RGBWW (RGB + White + Warm White) LED strip uses either a 5-in-1 LED chip with red, green, blue, white, and warm white for color mixing. The only difference between RGBW and RGBWW is the intensity of the white color. The term RGBCCT consists of RGB and CCT. CCT (Correlated Color Temperature) means that the color temperature of the led strip light can be adjusted to change between warm white and white. Thus, RGBWW strip light is another name of RGBCCT strip.

     

    RGBCW is the acronym for Red, Green, Blue, Cold, and Warm. These 5-in-1 chips are used in supper bright smart LED lighting products

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    Read more: Practical Aspects of Spectral Data and LEDs in Digital Content Production and Virtual Production – SIGGRAPH 2022
  • Ethan Roffler interviews CG Supervisor Daniele Tosti

    Ethan Roffler
    I recently had the honor of interviewing this VFX genius and gained great insight into what it takes to work in the entertainment industry. Keep in mind, these questions are coming from an artist’s perspective but can be applied to any creative individual looking for some wisdom from a professional. So grab a drink, sit back, and enjoy this fun and insightful conversation.



    Ethan

    To start, I just wanted to say thank you so much for taking the time for this interview!

    Daniele
    My pleasure.
    When I started my career I struggled to find help. Even people in the industry at the time were not that helpful. Because of that, I decided very early on that I was going to do exactly the opposite. I spend most of my weekends talking or helping students. ;)

    Ethan
    That’s awesome! I have also come across the same struggle! Just a heads up, this will probably be the most informal interview you’ll ever have haha! Okay, so let’s start with a small introduction!

    Daniele
    Short introduction: I worked very hard and got lucky enough to work on great shows with great people. ;) Slightly longer version: I started working for a TV channel, very early, while I was learning about CG. Slowly made my way across the world, working along very great people and amazing shows. I learned that to be successful in this business, you have to really love what you do as much as respecting the people around you. What you do will improve to the final product; the way you work with people will make a difference in your life.

    Ethan
    How long have you been an artist?

    Daniele
    Loaded question. I believe I am still trying and craving to be one. After each production I finish I realize how much I still do not know. And how many things I would like to try. I guess in my CG Sup and generalist world, being an artist is about learning as much about the latest technologies and production cycles as I can, then putting that in practice. Having said that, I do consider myself a cinematographer first, as I have been doing that for about 25 years now.

    Ethan
    Words of true wisdom, the more I know the less I know:) How did you get your start in the industry?
    How did you break into such a competitive field?

    Daniele
    There were not many schools when I started. It was all about a few magazines, some books, and pushing software around trying to learn how to make pretty images. Opportunities opened because of that knowledge! The true break was learning to work hard to achieve a Suspension of Disbelief in my work that people would recognize as such. It’s not something everyone can do, but I was fortunate to not be scared of working hard, being a quick learner and having very good supervisors and colleagues to learn from.

    Ethan
    Which do you think is better, having a solid art degree or a strong portfolio?

    Daniele
    Very good question. A strong portfolio will get you a job now. A solid strong degree will likely get you a job for a longer period. Let me digress here; Working as an artist is not about being an artist, it’s about making money as an artist. Most people fail to make that difference and have either a poor career or lack the understanding to make a stable one. One should never mix art with working as an artist. You can do both only if you understand business and are fair to yourself.



    Ethan

    That’s probably the most helpful answer to that question I have ever heard.
    What’s some advice you can offer to someone just starting out who wants to break into the industry?

    Daniele
    Breaking in the industry is not just about knowing your art. It’s about knowing good business practices. Prepare a good demo reel based on the skill you are applying for; research all the places where you want to apply and why; send as many reels around; follow up each reel with a phone call. Business is all about right time, right place.

    Ethan
    A follow-up question to that is: Would you consider it a bad practice to send your demo reels out in mass quantity rather than focusing on a handful of companies to research and apply for?

    Daniele
    Depends how desperate you are… I would say research is a must. To improve your options, you need to know which company is working on what and what skills they are after. If you were selling vacuum cleaners you probably would not want to waste energy contacting shoemakers or cattle farmers.

    Ethan
    What do you think the biggest killer of creativity and productivity is for you?

    Daniele
    Money…If you were thinking as an artist. ;) If you were thinking about making money as an artist… then I would say “thinking that you work alone”.

    Ethan
    Best. Answer. Ever.
    What are ways you fight complacency and maintain fresh ideas, outlooks, and perspectives

    Daniele
    Two things: Challenge yourself to go outside your comfort zone. And think outside of the box.

    Ethan
    What are the ways/habits you have that challenge yourself to get out of your comfort zone and think outside the box?

    Daniele
    If you think you are a good character painter, pick up a camera and go take pictures of amazing landscapes. If you think you are good only at painting or sketching, learn how to code in python. If you cannot solve a problem, that being a project or a person, learn to ask for help or learn about looking at the problem from various perspectives. If you are introvert, learn to be extrovert. And vice versa. And so on…

    Ethan
    How do you avoid burnout?

    Daniele
    Oh… I wish I learned about this earlier. I think anyone that has a passion in something is at risk of burning out. Artists, more than many, because we see the world differently and our passion goes deep. You avoid burnouts by thinking that you are in a long term plan and that you have an obligation to pay or repay your talent by supporting and cherishing yourself and your family, not your paycheck. You do this by treating your art as a business and using business skills when dealing with your career and using artistic skills only when you are dealing with a project itself.

    Ethan
    Looking back, what was a big defining moment for you?

    Daniele
    Recognizing that people around you, those being colleagues, friends or family, come first.
    It changed my career overnight.

    Ethan
    Who are some of your personal heroes?

    Daniele
    Too many to list. Most recently… James Cameron; Joe Letteri; Lawrence Krauss; Richard Dawkins. Because they all mix science, art, and poetry in their own way.

    Ethan
    Last question:
    What’s your dream job? ;)

    Daniele
    Teaching artists to be better at being business people… as it will help us all improve our lives and the careers we took…

    Being a VFX artist is fundamentally based on mistrust.
    This because schedules, pipelines, technology, creative calls… all have a native and naive instability to them that causes everyone to grow a genuine but beneficial lack of trust in the status quo. This is a fine balance act to build into your character. The VFX motto: “Love everyone but trust no one” is born on that.

     

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    Read more: Ethan Roffler interviews CG Supervisor Daniele Tosti
  • 3D Lighting Tutorial by Amaan Kram

    http://www.amaanakram.com/lightingT/part1.htm

    The goals of lighting in 3D computer graphics are more or less the same as those of real world lighting.

     

    Lighting serves a basic function of bringing out, or pushing back the shapes of objects visible from the camera’s view.
    It gives a two-dimensional image on the monitor an illusion of the third dimension-depth.

    But it does not just stop there. It gives an image its personality, its character. A scene lit in different ways can give a feeling of happiness, of sorrow, of fear etc., and it can do so in dramatic or subtle ways. Along with personality and character, lighting fills a scene with emotion that is directly transmitted to the viewer.

     

    Trying to simulate a real environment in an artificial one can be a daunting task. But even if you make your 3D rendering look absolutely photo-realistic, it doesn’t guarantee that the image carries enough emotion to elicit a “wow” from the people viewing it.

     

    Making 3D renderings photo-realistic can be hard. Putting deep emotions in them can be even harder. However, if you plan out your lighting strategy for the mood and emotion that you want your rendering to express, you make the process easier for yourself.

     

    Each light source can be broken down in to 4 distinct components and analyzed accordingly.

    · Intensity
    · Direction
    · Color
    · Size

     

    The overall thrust of this writing is to produce photo-realistic images by applying good lighting techniques.

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    Read more: 3D Lighting Tutorial by Amaan Kram
  • Photography basics: Exposure Value vs Photographic Exposure vs Il/Luminance vs Pixel luminance measurements

    Also 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.

     

    https://www.streetdirectory.com/travel_guide/141307/photography/exposure_value_ev_and_exposure_compensation.html

    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

    https://photo.stackexchange.com/questions/968/how-can-i-correctly-measure-light-using-a-built-in-camera-meter

    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:

    (more…)

    , ,
    Read more: Photography basics: Exposure Value vs Photographic Exposure vs Il/Luminance vs Pixel luminance measurements
  • domeble – Hi-Resolution CGI Backplates and 360° HDRI

    www.domeble.com/

    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.

     

    , ,
    Read more: domeble – Hi-Resolution CGI Backplates and 360° HDRI

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