grayscale in PS

killingpeople

why are the results different between a color image that has been desaturated using a hue/saturation adjustment, compared to the same color image that's [/i]image mode is set to grayscale[/i]? what does a hue/saturation adjustment do differently than setting an images' image mode to grayscale?

ScoobyDoofus

Could it be because a grayscale image recieves no adjustments from your color workspace in PS, while a color image you've desaturated is still subject to adjustments from the working or preview profile?

Slum

Yeah, I've found you lose a lot of value when doing "hue/saturation" (which has the same results as 'desaturate')

The best solution is to do what I did, and make an action that creates a new layer, fills it with black, sets it's transfer mode to color, and merges it down.

Eric Chadwick

The basic idea is 100% green is perceptually brighter than 100% blue, so it gets a higher luminance weight.

Grayscale mode uses the luminance weighting, but de-saturation uses equal weight per channel. Makes sense when you think about it, de-sat is doing just that and nothing else.

More info, incl the weights...
http://en.wikipedia.org/wiki/Luminance_%28relative%29

edit... oops, last link was wrong. Here are the weights that Grayscale Mode uses (I think).
http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale

Rob Galanakis

Also on general RGB-HSL conversion, http://www.mpa-garching.mpg.de/MPA-GRAPHICS/hsl-rgb.html