Saturation in Photoshop

[thomasthesen]

I have two fully saturated colours: yellow and ultramarine. If I reduce both their saturation to 0% I end up with two greys of the exactly the same tone.

But because yellow has a higher luminance than blue, shouldn't the yellow without any saturation be brighter than the blue?

[Moved from the Color management forum to a Photoshop forum - moderator]

[macpawel]

Maybe try to use Black White - adjustments - this way you can adjust any colors and prepare perfect grayscale picture

Pawel

[D Fosse · Accepted solution]

You're right, but this is how the RGB model works. It just averages values.

Convert to Lab first, and you'll get the inherent luminance right.

[thomasthesen]

Awesome! Thank you so much 😄

[TheDigitalDog]

Or just use the Fade Command after using Saturation in RGB, pick a blend mode like Color or Saturation. Not exactly the same as converting to Lab but, no conversion to Lab which is something you don’t want to do with 8-bit per color data!