![]() In film or a digital sensor there is a spectral sensitivity function that determine which frequencies of light get absorbed/sensitise the emulsion based upon the chemical structure. in film or any system sensitive to the electromagnetic spectrum, can be considered as a reduction of an infinite number of frequencies (well infinite depending on your quantum view of the world I guess), into a smaller number, in a similar manner to a weighted sum histogram. The answer is none of the above methods are used for film. If you found this post useful, check out for daily tidbits of signal and image processing. And sometimes the three methods produce very similar results. However, some images look better using one of the other algorithms. The luminosity method works best overall and is the default method used if you ask GIMP to change an image from RGB to grayscale from the Image -> Mode menu. The lightness method tends to reduce contrast. The example sunflower images below come from the GIMP documentation. The formula for luminosity is 0.21 R + 0.72 G + 0.07 B. We’re more sensitive to green than other colors, so green is weighted most heavily. It also averages the values, but it forms a weighted average to account for human perception. The luminosity method is a more sophisticated version of the average method. The average method simply averages the values: (R + G + B) / 3. The lightness method averages the most prominent and least prominent colors: (max(R, G, B) + min(R, G, B)) / 2. The Cancel button closes the dialog without accepting the color you selected as the foreground or background color.How do you convert a color image to grayscale? If each color pixel is described by a triple (R, G, B) of intensities for red, green, and blue, how do you map that to a single number giving a grayscale value? The GIMP image software has three algorithms. The Reset button rejects the selected color and lets you select another color.
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