Difference between saturation and greyscale.

[pinobot]

Can someone please explain the difference between lowering the saturation and greyscale.
I've tried to remove some banding on a layer and the two versions give different results.

Original:


Reducing saturation in 'Hue/Satuation/Lightness' to '-100':


greyscale:

[LeviFiction]

I did a search for your exact question and found some good explinations

http://forums.cgsociety.org/archive/ind ... 91622.html

Desaturate has no regard for the actual color information in the image. If different colors have the same Intensity value, they will all desaturate to the exact same shade of gray.

The Grayscale command has a more realistic conversion map that tends to make a more natural conversion to black and white.

Blue tends to appear darker than green or yellow, even if they have the same Intensity values.

The best method is using the Black & White command (Image > Adjustments > Black & White...)

This gives you complete control over the intensities of the gray values based on the color information in the image.

http://edknepleyphoto.com/2011/03/13/lu ... aturation/

2. How about grayscale? How is that computed?

Grayscale attempts to take into account how our vision perceives color. We do not perceive all colors as being equally bright – green is seen as being brighter than red which is brighter than blue.

In order to convert colors to match the colors the way that we see them (more or less) we can’t simply average all three colors equally as in the desaturation method.
We must weight each color proportionally to how our eyes see them.
The accepted weightings are 30% of the red value, 59% of the green value, and 11% of the blue value – and not equal weights as in desaturation.
The weighted average gives us the grayscale shown in the lower left of the above example.

Often, it is difficult to see a difference between the luminance and grayscale versions – I wanted to use the above RGB test panel example to assure you that there is one.

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Which conversion should you use?

As I said, it depends. On what? On which provides the result that YOU want. That’s all that matters.

Myself, I see no redeeming virtue in desaturation and would never use it. Between the other two I tend to prefer the luminosity technique. I’m still researching details on grayscale vs. luminance when it comes to human vision considerations – something for a later post.

[pinobot]

Thanks.
Even though the blue bands are lighter instead of darker in the hue corrected image.