COLOR

LIGHTING

  • 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.

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

     

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