COLOR

LIGHTING

  • Eye retina’s Bipolar Cells, Horizontal Cells, and Photoreceptors

    In the retina, photoreceptors, bipolar cells, and horizontal cells work together to process visual information before it reaches the brain. Here’s how each cell type contributes to vision:

     

    1. Photoreceptors

    • Types: There are two main types of photoreceptors: rods and cones.
      • Rods: Specialized for low-light and peripheral vision; they help us see in dim lighting and detect motion.
      • Cones: Specialized for color and detail; they function best in bright light and are concentrated in the central retina (the fovea), allowing for high-resolution vision.
    • Function: Photoreceptors convert light into electrical signals. When light hits the retina, photoreceptors undergo a chemical change, triggering an electrical response that initiates the visual process. Rods and cones detect different intensities and colors, providing the foundation for brightness and color perception.

     

    2. Bipolar Cells

    • Function: Bipolar cells act as intermediaries, connecting photoreceptors to ganglion cells, which send signals to the brain. They receive input from photoreceptors and relay it to the retinal ganglion cells.
    • On and Off Bipolar Cells: Some bipolar cells are ON cells, responding when light is detected (depolarizing in light), and others are OFF cells, responding in darkness (depolarizing in the absence of light). This division allows for more precise contrast detection and the ability to distinguish light from dark areas in the visual field.

     

    3. Horizontal Cells

    • Function: Horizontal cells connect photoreceptors to each other and create lateral interactions between them. They integrate signals from multiple photoreceptors, allowing them to adjust the sensitivity of neighboring photoreceptors in response to varying light conditions.
    • Lateral Inhibition: This process improves visual contrast and sharpness by making the borders between light and dark areas more distinct, enhancing our ability to perceive edges and fine detail.

     

    These three types of cells work together to help the retina preprocess visual information and perception, emphasizing contrast and adjusting for different lighting conditions before signals are sent to the brain for further processing and interpretation.

     

     

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    Read more: Eye retina’s Bipolar Cells, Horizontal Cells, and Photoreceptors
  • Photography basics: Why Use a (MacBeth) Color Chart?

    Start here: https://www.pixelsham.com/2013/05/09/gretagmacbeth-color-checker-numeric-values/

     

    https://www.studiobinder.com/blog/what-is-a-color-checker-tool/

     

     

     

     

    In LightRoom

     

    in Final Cut

     

    in Nuke

    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.

     

    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.

     

    This will set the sun usually around EV12-17 and the sky EV1-4 , depending on cloud coverage.

     

    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.

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    Read more: Photography basics: Why Use a (MacBeth) Color Chart?
  • HDRI shooting and editing by Xuan Prada and Greg Zaal

    www.xuanprada.com/blog/2014/11/3/hdri-shooting

     

    http://blog.gregzaal.com/2016/03/16/make-your-own-hdri/

     

    http://blog.hdrihaven.com/how-to-create-high-quality-hdri/

     

    Shooting checklist

    • Full coverage of the scene (fish-eye shots)
    • Backplates for look-development (including ground or floor)
    • Macbeth chart for white balance
    • Grey ball for lighting calibration
    • Chrome ball for lighting orientation
    • Basic scene measurements
    • Material samples
    • Individual HDR artificial lighting sources if required

    Methodology

    • Plant the tripod where the action happens, stabilise it and level it
    • Set manual focus
    • Set white balance
    • Set ISO
    • Set raw+jpg
    • Set apperture
    • Metering exposure
    • Set neutral exposure
    • Read histogram and adjust neutral exposure if necessary
    • Shot slate (operator name, location, date, time, project code name, etc)
    • Set auto bracketing
    • Shot 5 to 7 exposures with 3 stops difference covering the whole environment
    • Place the aromatic kit where the tripod was placed, and take 3 exposures. Keep half of the grey sphere hit by the sun and half in shade.
    • Place the Macbeth chart 1m away from tripod on the floor and take 3 exposures
    • Take backplates and ground/floor texture references
    • Shoot reference materials
    • Write down measurements of the scene, specially if you are shooting interiors.
    • If shooting artificial lights take HDR samples of each individual lighting source.

    Exposures starting point

    • Day light sun visible ISO 100 F22
    • Day light sun hidden ISO 100 F16
    • Cloudy ISO 320 F16
    • Sunrise/Sunset ISO 100 F11
    • Interior well lit ISO 320 F16
    • Interior ambient bright ISO 320 F10
    • Interior bad light ISO 640 F10
    • Interior ambient dark ISO 640 F8
    • Low light situation ISO 640 F5

     

    NOTE: The goal is to clean the initial individual brackets before or at merging time as much as possible.
    This means:

    • keeping original shooting metadata
    • de-fringing
    • removing aberration (through camera lens data or automatically)
    • at 32 bit
    • in ACEScg (or ACES) wherever possible

     

    Here are the tips for using the chromatic ball in VFX projects, written in English:
    https://www.linkedin.com/posts/bellrodrigo_here-are-the-tips-for-using-the-chromatic-activity-7200950595438940160-AGBp

     

    Tips for Using the Chromatic Ball in VFX Projects**

    The chromatic ball is an invaluable tool in VFX work, helping to capture lighting and reflection data crucial for integrating CGI elements seamlessly. Here are some tips to maximize its effectiveness:

     

    1. **Positioning**:
    – Place the chromatic ball in the same lighting conditions as the main subject. Ensure it is visible in the camera frame but not obstructing the main action.
    – Ideally, place the ball where the CGI elements will be integrated to match the lighting and reflections accurately.

     

    2. **Recording Reference Footage**:
    – Capture reference footage of the chromatic ball at the beginning and end of each scene or lighting setup. This ensures you have consistent lighting data for the entire shoot.

     

    3. **Consistent Angles**:
    – Use consistent camera angles and heights when recording the chromatic ball. This helps in comparing and matching lighting setups across different shots.

     

    4. **Combine with a Gray Ball**:
    – Use a gray ball alongside the chromatic ball. The gray ball provides a neutral reference for exposure and color balance, complementing the chromatic ball’s reflection data.

     

    5. **Marking Positions**:
    – Mark the position of the chromatic ball on the set to ensure consistency when shooting multiple takes or different camera angles.

     

    6. **Lighting Analysis**:
    – Analyze the chromatic ball footage to understand the light sources, intensity, direction, and color temperature. This information is crucial for creating realistic CGI lighting and shadows.

     

    7. **Reflection Analysis**:
    – Use the chromatic ball to capture the environment’s reflections. This helps in accurately reflecting the CGI elements within the same scene, making them blend seamlessly.

     

    8. **Use HDRI**:
    – Capture High Dynamic Range Imagery (HDRI) of the chromatic ball. HDRI provides detailed lighting information and can be used to light CGI scenes with greater realism.

     

    9. **Communication with VFX Team**:
    – Ensure that the VFX team is aware of the chromatic ball’s data and how it was captured. Clear communication ensures that the data is used effectively in post-production.

     

    10. **Post-Production Adjustments**:
    – In post-production, use the chromatic ball data to adjust the CGI elements’ lighting and reflections. This ensures that the final output is visually cohesive and realistic.

    , ,
    Read more: HDRI shooting and editing by Xuan Prada and Greg Zaal

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