COLOR

  • Image rendering bit depth

    The 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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  • PBR Color Reference List for Materials – by Grzegorz Baran

    The list should be helpful for every material artist who work on PBR materials as it contains over 200 color values measured with PCE-RGB2 1002 Color Spectrometer device and presented in linear and sRGB (2.2) gamma space.

    All color values, HUE and Saturation in this list come from measurements taken with PCE-RGB2 1002 Color Spectrometer device and are presented in linear and sRGB (2.2) gamma space (more info at the end of this video) I calculated Relative Luminance and Luminance values based on captured color using my own equation which takes color based luminance perception into consideration. Bare in mind that there is no ‘one’ color per substance as nothing in nature is even 100% uniform and any value in +/-10% range from these should be considered as correct one. Therefore this list should be always considered as a color reference for material’s albedos, not ulitimate and absolute truth.

     

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    Read more: PBR Color Reference List for Materials – by Grzegorz Baran
  • About color: What is a LUT

    http://www.lightillusion.com/luts.html

    https://www.shutterstock.com/blog/how-use-luts-color-grading

     

    A LUT (Lookup Table) is essentially the modifier between two images, the original image and the displayed image, based on a mathematical formula. Basically conversion matrices of different complexities. There are different types of LUTS – viewing, transform, calibration, 1D and 3D.

     

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  • colorhunt.co

    Color Hunt is a free and open platform for color inspiration with thousands of trendy hand-picked color palettes.

    colorhunt.co/

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  • Polarised vs unpolarized filtering

    A light wave that is vibrating in more than one plane is referred to as unpolarized light. …

    Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization.

    en.wikipedia.org/wiki/Polarizing_filter_(photography)

    The most common use of polarized technology is to reduce lighting complexity on the subject.
    Details such as glare and hard edges are not removed, but greatly reduced.

    This method is usually used in VFX to capture raw images with the least amount of specular diffusion or pollution, thus allowing artists to infer detail back through typical shading and rendering techniques and on demand.

    Light reflected from a non-metallic surface becomes polarized; this effect is maximum at Brewster’s angle, about 56° from the vertical for common glass.

    A polarizer rotated to pass only light polarized in the direction perpendicular to the reflected light will absorb much of it. This absorption allows glare reflected from, for example, a body of water or a road to be reduced. Reflections from shiny surfaces (e.g. vegetation, sweaty skin, water surfaces, glass) are also reduced. This allows the natural color and detail of what is beneath to come through. Reflections from a window into a dark interior can be much reduced, allowing it to be seen through. (The same effects are available for vision by using polarizing sunglasses.)

     

    www.physicsclassroom.com/class/light/u12l1e.cfm

     

    Some of the light coming from the sky is polarized (bees use this phenomenon for navigation). The electrons in the air molecules cause a scattering of sunlight in all directions. This explains why the sky is not dark during the day. But when looked at from the sides, the light emitted from a specific electron is totally polarized.[3] Hence, a picture taken in a direction at 90 degrees from the sun can take advantage of this polarization.

    Use of a polarizing filter, in the correct direction, will filter out the polarized component of skylight, darkening the sky; the landscape below it, and clouds, will be less affected, giving a photograph with a darker and more dramatic sky, and emphasizing the clouds.

     

    There are two types of polarizing filters readily available, linear and “circular”, which have exactly the same effect photographically. But the metering and auto-focus sensors in certain cameras, including virtually all auto-focus SLRs, will not work properly with linear polarizers because the beam splitters used to split off the light for focusing and metering are polarization-dependent.

     

    Polarizing filters reduce the light passed through to the film or sensor by about one to three stops (2–8×) depending on how much of the light is polarized at the filter angle selected. Auto-exposure cameras will adjust for this by widening the aperture, lengthening the time the shutter is open, and/or increasing the ASA/ISO speed of the camera.

     

    www.adorama.com/alc/nd-filter-vs-polarizer-what%25e2%2580%2599s-the-difference

     

    Neutral Density (ND) filters help control image exposure by reducing the light that enters the camera so that you can have more control of your depth of field and shutter speed. Polarizers or polarizing filters work in a similar way, but the difference is that they selectively let light waves of a certain polarization pass through. This effect helps create more vivid colors in an image, as well as manage glare and reflections from water surfaces. Both are regarded as some of the best filters for landscape and travel photography as they reduce the dynamic range in high-contrast images, thus enabling photographers to capture more realistic and dramatic sceneries.

     

    shopfelixgray.com/blog/polarized-vs-non-polarized-sunglasses/

     

    www.eyebuydirect.com/blog/difference-polarized-nonpolarized-sunglasses/

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  • 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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LIGHTING