This week's banner is by Frank from Nova Scotia, Canada

Problems and solutions
Back to the book | Post New Topic | Search | Help | Log In | Register

» Forum Index » Problems and solutions » Topic: Using curves with greyscale - a possibly dumb question.

Posted on 18/01/22 10:36:48 AM
DavidMac
Director of Photoshop
Posts: 3932

Reply


Using curves with greyscale - a possibly dumb question.
Here's what may prove to be an extremely dumb question from someone who has used PS for well over twenty years.

Can anyone tell me why the curves adjustment is reversed in Greyscale mode? If you don't know what I mean by this try converting an image to greyscale and then apply the curves adjustment. The input and output bars to the left and bottom of the curve are reversed with white in the bottom left corner. This means that raising the curve darkens the image and lowering the curve lightens it. The exact reverse of what we expect in normal RGB usage. All other adjustments seem to work in greyscale exactly as expected.

So why?

_________________
The subtlety and conviction of any Photoshop effect is invariably inversely proportional to the number of knobs on it .......

Posted on 18/01/22 7:23:43 PM
AvaB
*
Posts: 1

Reply
Re: Using curves with greyscale - a possibly dumb question.
DavidMac,

Don’t know why or even when the Adobe PS engineers decided to change the Curves, gradient ramp, with an Image>Mode>Grayscale file.
Actually, I have never noticed that either.

It’s because in Curves you have Pigment/Ink% chosen rather than Light (0-255) in the upper right

To change in your file:
Curves (fly-out menu), select Curves Display Options….
Select Light (0-255).
The default is set to Pigment/ink


Posted on 18/01/22 8:46:40 PM
DavidMac
Director of Photoshop
Posts: 3932

Reply


Re: Using curves with greyscale - a possibly dumb question.
AvaB

Yours is not a name I recognise from our regular contributors so first off "Hello"! Delighted to hear from you.

So I looked at your suggestion and "Bingo" suddenly all is revealed. I work only for screen and never (with rare exceptions) for print. The mysteries of pigment/ink are opaque to me. I have now switched options to suit my screen oriented working methods.

Strangely, after posting, but before seeing your reply, I played with some other modes to see how curves behaved with them and discovered that CMYK behaved in the same 'reversed' manner. So I was coming to the conclusion that it might be print related but had absolutely no idea how.

As to why Adobe chose this as greyscale default I can only suppose that Adobe presume that greyscale is likely to be prioritised in print more than in screen output. Who knows?

Thank you so much for solving a mystery for me and for doing it so concisely and clearly.

So any of the forum regulars who know me and see this, how many of you could have answered? Be honest!

I'll put my money on Steve and Frank.

_________________
The subtlety and conviction of any Photoshop effect is invariably inversely proportional to the number of knobs on it .......

Posted on 18/01/22 8:55:12 PM
Steve Caplin
Administrator
Posts: 6526

Reply


Re: Using curves with greyscale - a possibly dumb question.
Great answer! Thanks AvaB - really concise and to the point.

Posted on 19/01/22 10:50:33 PM
Frank
Eager Beaver
Posts: 1183

Reply


Re: Using curves with greyscale - a possibly dumb question.
Yes David, I have seen this in the past but truthfully I would have to look it up again to refresh an old memory. Not a setting I would use.
While we are on curves here's a good change I would recommend:

CURVES ALGORITHM
PS Curves under the AUTO button uses “Enhance Brightness and Contrast” .
To change this Hold the OPT key and click on AUTO and change to “ Find Dark and Light Colors”
This is a better algorithm so set this one as your default (check “Save as defaults) and also check “Snap Neutral Midtones”
If you find this doesn’t work on a particular image then click on the center eyedropper and click on a neutral gray in the image (also try the white or black eyedroppers)
Why not just click using the eyedroppers right off the bat - you would still need to adjust the contrast using the curves.
NOTE: You can use the ARROW KEYS on the keyboard to nudge your curve points after you place them - to nudge faster use the SHIFT KEY - you can also use the PLUS or Minus Keys to jump between selected points


Posted on 20/01/22 12:23:17 PM
DavidMac
Director of Photoshop
Posts: 3932

Reply


Re: Using curves with greyscale - a possibly dumb question.
Very interesting Frank. I knew none of this.

The truth is I never touch the "Auto" buttons on any adjustments or filters as experience has shown me that they are rarely to my personal liking.

That's a rather stupid prejudicial attitude, but my approach to all the adjustments is very non technical and tends be mostly on the basis of "Pinch it and see if it squeals".

_________________
The subtlety and conviction of any Photoshop effect is invariably inversely proportional to the number of knobs on it .......

Posted on 20/01/22 3:40:48 PM
Frank
Eager Beaver
Posts: 1183

Reply


Re: Using curves with greyscale - a possibly dumb question.
I agree, I seldom use Auto but this one to me is a recommended setting - try it on a few images - "sometimes" Auto can be a good starting point

Posted on 20/01/22 4:45:54 PM
DavidMac
Director of Photoshop
Posts: 3932

Reply


Re: Using curves with greyscale - a possibly dumb question.
Thanks Frank. Yours is advice I trust.

I will take a proper look and have a go.

Truth is I do very little pure photo correction. Most of my PS work is compositing or transformation for which one tends to approach adjustments differently. I would guess that, despite my profession, many of the people in this group know far more about correction than I ever will.

_________________
The subtlety and conviction of any Photoshop effect is invariably inversely proportional to the number of knobs on it .......

Posted on 21/01/22 11:44:37 AM
Frank
Eager Beaver
Posts: 1183

Reply


Re: Using curves with greyscale - a possibly dumb question.
You're too modest - putting out some great work.

Posted on 21/01/22 11:52:28 AM
DavidMac
Director of Photoshop
Posts: 3932

Reply


Re: Using curves with greyscale - a possibly dumb question.
Well thank you. But there's always so much more to learn.

_________________
The subtlety and conviction of any Photoshop effect is invariably inversely proportional to the number of knobs on it .......
Back

[ To post a reply, please Log In or Register ]

Powered by SimpleForum Pro 4.6