COLOR

LIGHTING

  • Is a MacBeth Colour Rendition Chart the Safest Way to Calibrate a Camera?

    www.colour-science.org/posts/the-colorchecker-considered-mostly-harmless/

     

     

    “Unless you have all the relevant spectral measurements, a colour rendition chart should not be used to perform colour-correction of camera imagery but only for white balancing and relative exposure adjustments.”

     

    “Using a colour rendition chart for colour-correction might dramatically increase error if the scene light source spectrum is different from the illuminant used to compute the colour rendition chart’s reference values.”

     

    “other factors make using a colour rendition chart unsuitable for camera calibration:

    – Uncontrolled geometry of the colour rendition chart with the incident illumination and the camera.
    – Unknown sample reflectances and ageing as the colour of the samples vary with time.
    – Low samples count.
    – Camera noise and flare.
    – Etc…

     

    “Those issues are well understood in the VFX industry, and when receiving plates, we almost exclusively use colour rendition charts to white balance and perform relative exposure adjustments, i.e. plate neutralisation.”

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  • Convert between light exposure and intensity

    import math,sys
    
    def Exposure2Intensity(exposure): 
        exp = float(exposure)
        result = math.pow(2,exp)
        print(result)
    
    Exposure2Intensity(0)
    
    def Intensity2Exposure(intensity):
        inarg = float(intensity)
        
        if inarg == 0:
            print("Exposure of zero intensity is undefined.")
            return
        
        if inarg < 1e-323:
            inarg = max(inarg, 1e-323)
            print("Exposure of negative intensities is undefined. Clamping to a very small value instead (1e-323)")
        
        result = math.log(inarg, 2)
        print(result)
    
    Intensity2Exposure(0.1)
    
    
    
    
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  • 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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  • 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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