Setting the purple-with-turquoise-polka-dots point…

From: (Don)

Given a point with, say R=12, G=23, B=45 which I know should be, say, R=56, G=78, B=23 how do I set this very point to that exact color and have this change applied to the rest of the image?

Try Curves … work on each channel separately in Curves (ie, in the Channel drop-down menu at the top of the Curves dialog box pick each channel one at a time), click on the color you wish to change while holding down the Ctrl key, which will place a point on that color at the appropriate spot on the curve, and in the lower left of the Curves dialog box change the "Output" value to the new number.

Work on an adjustment layer so you can tweak it as necessary.

For example, the problem with color balance dialog is that it goes from -100 to +100 while (in my case) a color goes from 0 to 255.

Color Balance is a linear tool, meaning it moves all values a fixed amount, and this rarely gives results as good as a non-linear tool like Curves.

Bill

If you have the full Photoshop (as opposed to Elements or LE) you can use the arrow keys to move a curve point around.

Make sure the Info palette is showing. In Curves, control (Mac=command) – shift – click the color you wish to change. This puts a point on each of the channels, corresponding to the color you clicked. Leave your cursor parked over that point.

Now go to each channel in turn (ctrl/command-1 through 3) and use the arrow keys to move your point. Watch the Info readout until you have the number you want. Repeat for each of the other channels.

Depending on what you’re doing, this may give too much of a curve to the channels. In general, the closer your point is to the end of the curve, the more it will mess up the rest of the curve. In that case, click the extreme end of the curve and proceed as before.

This is all much faster to do than to explain. IOW, if your textured white is off, move the end point on the white side. Keep your cursor on your textured white area. You’re moving the pure white part of the curve until the off-white is what you want it.

Let me know if it’s still unclear.

Tom Nelson
Tom Nelson Photography

In article , Don
wrote:

Seriously, though, how do I set points other than black and white?
I’m referring to color balancing aspect of setting the black and white points but applied to other colors. What I mean is this:
Given a point with, say R=12, G=23, B=45 which I know should be, say, R=56, G=78, B=23 how do I set this very point to that exact color and have this change applied to the rest of the image? (These are totally arbitrary numbers just as an example.)

Sure, I can come up with values by experimentation and trial and error, but that’s both too time consuming and inexact.

For example, the problem with color balance dialog is that it goes from -100 to +100 while (in my case) a color goes from 0 to 255.
Again, calculating intermediate values is simple math, but is this linear? Etc… Etc… But why re-invent the wheel, so…
How do I specify (using exact RGB values) what a certain point should be and have that modification applied to the rest of the image?
Thanks as always!

Don.

First off, thank you both for writing!

On Wed, 11 Feb 2004 03:39:30 -0600, Tom Nelson
wrote:

If you have the full Photoshop (as opposed to Elements or LE) you can use the arrow keys to move a curve point around.

I have PS 6 here (Windows version).

Make sure the Info palette is showing. In Curves, control (Mac=command) – shift – click the color you wish to change. This puts a point on each of the channels, corresponding to the color you clicked. Leave your cursor parked over that point.

OK, gotcha! One thing though, sample size must be set to Point Sample!!! Gets me every time! 🙂

Now go to each channel in turn (ctrl/command-1 through 3) and use the arrow keys to move your point. Watch the Info readout until you have the number you want. Repeat for each of the other channels.

So far, so good…

Depending on what you’re doing, this may give too much of a curve to the channels. In general, the closer your point is to the end of the curve, the more it will mess up the rest of the curve. In that case, click the extreme end of the curve and proceed as before.

That’s indeed what happened. Is there a way to do this in a linear fashion? As in: removing a cast by setting an arbitrary pixel to a specific value and then have the same change applied to the whole image in a linear fashion.

This is all much faster to do than to explain. IOW, if your textured white is off, move the end point on the white side. Keep your cursor on your textured white area. You’re moving the pure white part of the curve until the off-white is what you want it.

Let me know if it’s still unclear.

Oh no, it was perfectly clear! Thanks very much, indeed!

Don.

Tom Nelson
Tom Nelson Photography

In article , Don
wrote:

Seriously, though, how do I set points other than black and white?
I’m referring to color balancing aspect of setting the black and white points but applied to other colors. What I mean is this:
Given a point with, say R=12, G=23, B=45 which I know should be, say, R=56, G=78, B=23 how do I set this very point to that exact color and have this change applied to the rest of the image? (These are totally arbitrary numbers just as an example.)

Sure, I can come up with values by experimentation and trial and error, but that’s both too time consuming and inexact.

For example, the problem with color balance dialog is that it goes from -100 to +100 while (in my case) a color goes from 0 to 255.
Again, calculating intermediate values is simple math, but is this linear? Etc… Etc… But why re-invent the wheel, so…
How do I specify (using exact RGB values) what a certain point should be and have that modification applied to the rest of the image?
Thanks as always!

Don.

In article , Don
wrote:

On Wed, 11 Feb 2004 03:39:30 -0600, Tom Nelson
wrote:

Depending on what you’re doing, this may give too much of a curve to the channels. In general, the closer your point is to the end of the curve, the more it will mess up the rest of the curve. In that case, click the extreme end of the curve and proceed as before.

That’s indeed what happened. Is there a way to do this in a linear fashion? As in: removing a cast by setting an arbitrary pixel to a specific value and then have the same change applied to the whole image in a linear fashion.

Adjust>Color Balance will do this, sort of. Set the Info palette to show HSB (hue, saturation and brightness). In the Color Balance dialog, click in the numerical field for Hue, then hover your cursor over the color you wish to change and watch the Info palette. You can change the hue number with the up and down arrow keys.

Changing the hue does not match brightness and saturation, of course. Keep in mind that adjusting brightness with Color Balance is discouraged because of the likelihood of pushing other pixels to pure black or white while you’re messing with the color you’re adjusting. You might want to match hue and saturation in Color Balance, then go back to Curves to set the brightness.

Tom Nelson
Tom Nelson Photography

On Thu, 12 Feb 2004 13:04:41 -0600, Tom Nelson
wrote:

Is there a way to do this in a linear
fashion? As in: removing a cast by setting an arbitrary pixel to a specific value and then have the same change applied to the whole image in a linear fashion.

Adjust>Color Balance will do this, sort of. Set the Info palette to show HSB (hue, saturation and brightness). In the Color Balance dialog, click in the numerical field for Hue, then hover your cursor over the color you wish to change and watch the Info palette. You can change the hue number with the up and down arrow keys.

Changing the hue does not match brightness and saturation, of course. Keep in mind that adjusting brightness with Color Balance is discouraged because of the likelihood of pushing other pixels to pure black or white while you’re messing with the color you’re adjusting. You might want to match hue and saturation in Color Balance, then go back to Curves to set the brightness.

Thanks Tom!

Don.