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Only 3 bits are used for the red channel in the left two images, 8 bits in the right image. Colour banding is a subtle form of posterization in digital images, caused by the colour of each pixel being rounded to the nearest of the digital colour levels. While posterization is often done for artistic effect, colour banding is an undesired artifact.
If the original image is a photograph, it is likely to have thousands or even millions of distinct colors. The process of constraining the available colors to a specific color palette effectively throws away a certain amount of color information. A number of factors can affect the resulting quality of a color-reduced image.
For artistic effect, most image editing programs provide a posterization feature, or photographic processes may be used. Unwanted posterization, also known as banding, may occur when the color depth, sometimes called bit depth, is insufficient to accurately sample a continuous gradation of color tone. As a result, a continuous gradient appears ...
Image quality can be assessed using objective or subjective methods. In the objective method, image quality assessments are performed by different algorithms that analyze the distortions and degradations introduced in an image. Subjective image quality assessments are a method based on the way in which humans experience or perceive image quality.
where , , and are the color balanced red, green, and blue components of a pixel in the image; ′, ′, and ′ are the red, green, and blue components of the image before color balancing, and ′, ′, and ′ are the red, green, and blue components of a pixel which is believed to be a white surface in the image before color balancing.
True-color Kodak test images — The Kodak set in PNG format TESTIMAGES — Large collection of sample images designed for analysis and quality assessment of different kinds of displays (i.e. monitors, televisions and digital cinema projectors) and image processing techniques
A flat-field image is acquired by imaging a uniformly-illuminated screen, thus producing an image of uniform color and brightness across the frame. For handheld cameras, the screen could be a piece of paper at arm's length, but a telescope will frequently image a clear patch of sky at twilight, when the illumination is uniform and there are few ...
Test cards typically contain a set of patterns to enable television cameras and receivers to be adjusted to show the picture correctly (see SMPTE color bars).Most modern test cards include a set of calibrated color bars which will produce a characteristic pattern of "dot landings" on a vectorscope, allowing chroma and tint to be precisely adjusted between generations of videotape or network feeds.