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Jim Collier > X6XUTPd1: Grayscale method perceptual accuracy: original
Jim Collier > X6XUTPc2: Grayscale method perceptual accuracy: desaturate
Jim Collier > X6XUTPc1: Grayscale method perceptual accuracy: original
Jim Collier > X6XUTPb2: Grayscale method perceptual accuracy: Photoshop grayscale (Image | Mode | Grayscale). Depending on your color perception (which can vary wildly among individuals even those with no physical color deficiencies), you will most likely find this the most "accurate" grayscale conversion.
Jim Collier > X6XUTPb1: Grayscale method perceptual accuracy: originalThe following six images alternate between copies of this original color image, and three different grayscale images. It demonstrate the perceptual differences between the three most common grayscale conversion methods in Photoshop (also in many other editors).The test demonstrate the superiority of the Photoshop "Grayscale" convert method of getting a black-and-white image, when it comes to most accurately mimicking human perception.The basic problem is that the human eye does not perceive all colors of equal brightness to be equally intense&mdash;but colors of equal brightness are represented on the computer with mathematically equal luminosities. (E.g. #FF0088 vs. #88FF00; different colors, equal luminosities.).The Photoshop grayscale convert method takes this into account with a calibrated algorithm.In contrast, "Desaturate" simply removes color information while preserving the mathematical luminosity, which is inaccurate perceptually.These tests vividly demonstrate that converting to Lab Color space and isolating the Lightness channel is definitely the worst of these three most common methods, in terms of mimicking human perception for grayscale conversion. And that's not just because it's too bright&mdash;even when compensated for with brightness/contrast or curves, it just cannot be easily made to approximate natural perception. However, this shouldn't be read as implying that Lab Color is inferior as a colorspace ("the best colorspace" is an entirely different debate).The inferiority of the Lab Color Lightness channel is notable because there is a popular notion among serious photographers/editors that it is "The" superior method for arriving at a grayscale image.In the final analysis, if your only goal is to convert an image to grayscale, any of the three methods can work just fine. A color mixer can work just fine too. Perceptual accuracy is usually less important than artistic expression anyway, especially with black and white. And Photoshop has a hotkey combination for quickly desaturating an image, which makes it an awfully convenient method for getting black and white, even if it's not the most accurate. However, if your goal is to obtain a perceptually accurate grayscale image for intermediate processing layers (e.g. performing a contrast mask), then you are going to get more accurate results with "Grayscale" convert.Plus you just have to marvel at a calibration image that features two lightsabers prominently&mdash;or maybe they are just flashlights.
Jim Collier > X6XUTPd2: Grayscale method perceptual accuracy: Lab Color, Lightness channel
X6XUTPd1: Grayscale method perceptual accuracy: original
Jim Collier > X6XUTPd1: Grayscale method perceptual accuracy: original
X6XUTPd1: Grayscale method perceptual accuracy: original
See photo in original gallery.
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