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Curves to control saturation possible?

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  #1  
Old 11-28-2005, 11:29 AM
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saberlancer saberlancer is offline
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Curves to control saturation possible?

Hi,
I've been using curves to control contrast/brightness and some color change BUT then using hue/saturation whenever I want to change saturation.

Does anyone know how to use curves to change saturation or if you can point me to some tutorials?

Thank you and much appreciated..
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Old 11-28-2005, 12:00 PM
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Have you tried the LAB colorspace. If you do curves in LAB, on the AB channels you will control saturation. It takes a little getting used to but it's well worth it to learn.
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Old 11-28-2005, 07:23 PM
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OIC! Been curious about LAB after reading on forum abt it...
Now thats a good reason for me to get off my ass and learn it! Thanks!

But I reckon it won't offer as much flexibility as having both curves & Hue/saturation(used only for saturation) adjustment layers? As then I'll have 2 mask instead of only 1 curve 'mask' to adjust if I'm using LAB..?

Erm, hope I'm clear above,kekeke...
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Old 11-28-2005, 07:30 PM
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For a saturation curve, I recommend RGB mode. While Lab is good, it is not condusive for 'linear' sat work. In order to extract saturation while in Lab, you have to get polar and PS can't do squared roots. Or trig for that matter.

Try this in RGB:
Extract sat to greyscale

Variation that I've been using lately:
- Extract saturation to greyscale
- On the grey sat layer, fill G and B with pure black
- Set blending mode to Saturation
- Click Curves to grey sat layer
- In Curves, go to R channel and tweak away

I like it. The weird thing is that it is not the same as using Curves set to Saturation mode.
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Old 11-28-2005, 07:37 PM
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LAB: Well worth a bit of effort to get used to it. Although we have come to regard RGB as the "natural" mode, actually it's natural only to your monitor.
For us, people, LAB is a lot more natural.

Your levels / curves adjustments will be done in the L channel.
You can still use the Hue / Saturation adjustment for the colours (without affecting the luminosity, as happens when in RGB) - or you can tweak the A,B colours with curves.
Using levels on the A and B channels is usually a bit too heavy-handed.

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Old 11-29-2005, 05:11 AM
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Quote:
You can still use the Hue / Saturation adjustment for the colours (without affecting the luminosity, as happens when in RGB)...
There is a trick to using Hue/Sat without affecting Lum. All you have to do is change the blending mode of Hue/Sat to Colour.

Basically dealing with two different colour spaces:
HSL, being the classic double-cone.
HsY, being the custom human perception-based HSL space that Photoshop uses.

Once you know which space Photoshop is using with the various tools and blending modes, not that hard to manipulate whichever 'channel' you want while leaving the rest alone.

(RGB, HSL, HsY, Lab - play with all of them until your eyeballs bleed.)

Or did I totally misunderstand what you said, byRo?
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