How can I get a greyscale image (using Photoshop or any other tool) that is an accurate representation of what I see when looking at a color image. When I use the B&W, desaturate, or grayscale option in PS, I don't get anywhere near the values that I see; for example a yellow and a lavender where the yellow looks lighter when I squint at them are very different when I have PS convert to B&W or grayscale. The yellow appears to be darker!
A digital camera photo with mode set to B&W of the screen shows the yellow to be lighter than the lavender by about the correct amount.
I assume that this has to do with the light energy reaction in the eye vs the value levels used in the RGB colors. It seems that this function is useful enough to graphic artists that there should be a way to do this.