Color to Grayscale

Comparing Color to Grayscale Methods

There are several methods of converting from color to so-called black and white. An application can offer an RGB channels mixer; or no choice but what the app does; or a drop-down list or buttons for various methods such as 'Luminance'. The GIMP offers a good few:

From the manual: 8.31. Desaturate

Here's how four of them look when applied to a good old Macbeth card color image:

At first glance, they look the same but have a close look at each card's third row of primary and secondary colors (blue, green, red, yellow, magenta, cyan):

In the upper images, there is little tonal difference between the patches. Which implies that mere color differences in an actual scene would show little contrast after conversion ... think pool balls ... a slightly brighter yellow patch at left, I reckon. Much more contrast in the lower images' third row - with the yellow sticking out like a sore thumb! The image at left showing noticeably more contrast than that at right, even in the light brown wall paneling. Of the four methods used, the lower left (luminance) looks best to me. Some might prefer the lighter rendering of the first two rows offered by the lower right (Value).

So now I know why the most commonly recommended method is 'Luminance'

Comments welcome!

I never liked that chart (yes, I know that it is the "industry standard"). Would you post some real life images processed this way?

I rarely convert to B&W but when I do, I play with the LR and the DXO presets. Which one works best depends on the scene and on my taste, of course.

I always use luminance unless I am seeking a special effect. I find it gives the most natural looking images for my taste.

Here is an example image converted to greyscale in GIMP using the Luminance option. I find it interesting to also look at the image with the greyscale information removed, so we are seeing just the colours (all normalised to maximum lightness).

The top image is with the luminance or brightness information removed and the colours made as bright as possible; the middle image is the luminance as a greyscale; the bottom image is the original.

In GIMP, luminance is a weighted average of the three colour channels that tries to emulate the brightness seen by the human eye. I believe luminance is not the technically correct term for this, but that is what GIMP uses.

I’ve been converting to black & white via LAB in Photoshop for more that 20 years.
Yes, I know that there are many ways to achieve this, but… as far as I’m concerned, it’s the only game in town. lol