Adobe Community: How to select a color accurately?

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May 24, 2010

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1. Trevor.Dennis,

May 4, 2012 1:26 AM in reply to Adrtghhjj

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Go to the Channels Panel, and Ctrl/Cnd click the Green channel icon. I'm interested in where you are going with this?

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2. c.pfaffenbichler,

May 4, 2012 1:30 AM in reply to Adrtghhjj

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Could you please post an example?

You could load the green Channel as a Selection (command-clicking it in the Channels Panel), switch to Quick Mask Mode (Q), use Image > Adjustments > Threshold and switch back out from Quick Mask Mode (Q).

Maybe the Blend if-settings could provide another work-around.

Edit: Ah, I probably misunderstood or rather misinterpreted; Trevor’s proposal may well suffice.

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3. Adrtghhjj,

May 4, 2012 3:59 AM in reply to Trevor.Dennis

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I need that so I can erase the Green component out of every color in the image. I was curious how it would look afterwards.

I have managed to select the green channel and make a selection from it but I don't know how to erase it, or parts of it.

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4. c.pfaffenbichler,

May 4, 2012 4:03 AM in reply to Adrtghhjj

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Just to make sure: Are you talking about the Green Channel in RGB (and do you comprehend what it means) or are you talking about the color perception »green«?

Could you please post an example?

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5. Adrtghhjj,

May 4, 2012 6:27 AM in reply to c.pfaffenbichler

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Could you please post an example?

As example, I have made a green gradient. The 1st (leftmost) color is pure green, the last (rightmost) is black. Inbetween, ever darkening shades of green.

I need that green gradient to be replaced with blue: all the *green* in the gradient should be replaced by darker and darker shades of *blue*, all the way to black.

The Replace Color effect in PS seemed to fit, but there you can only select the Source color (green) and then move the Hue slider in a not-so-accurate way. I need to be able to accurately select my Destination color (blue) too, as I need a specific nuance of blue.

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6. c.pfaffenbichler,

May 4, 2012 6:39 AM in reply to Adrtghhjj

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You know one can post images on this Forum?

If you create the gradient it would naturally be best to do so with a Gradient Layer and just edit that as needed later on.

But assuming this is not the case have you tried a Hue Adjustment Layer and selected »Green« (or if the image contains only the gradient keep it set to »Master«)?

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7. Noel Carboni,

May 4, 2012 9:46 AM in reply to Adrtghhjj

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Adrtghhjj wrote:

I need that so I can erase the Green component out of every color in the image. I was curious how it would look afterwards.
I have managed to select the green channel and make a selection from it but I don't know how to erase it, or parts of it.

A point of confusion here may be that Adrtghhjj hasn't realized that all colors other than those made with combinations of pure red and blue contain some data in the green channel. Christoph's question in post 4 is right on target, and particularly important to get a precise answer for.

So, for example, note that the green channel of this orange-red color contains a non-zero green channel value, even though the color does not look green:

-Noel

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8. Adrtghhjj,

May 4, 2012 11:23 AM in reply to Noel Carboni

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A point of confusion here may be that Adrtghhjj hasn't realized that all colors other than those made with combinations of pure red and blue contain some data in the green channel. Christoph's question in post 4 is right on target, and particularly important to get a precise answer for.

Thanks for the info.

Yes, I was aware of that. I meant "all greens" as in "colors that contain a non-zero Green channel, even if the *color* green is invisible or barely visible".

E.g. I would consider color (R 255, G 1, B 255) as containing green.

In fact my original question concerned the process involved in making this color above reach the value of (R 255, G 0, B 255).

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9. Noel Carboni,

May 4, 2012 11:32 AM in reply to Adrtghhjj

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Well, if you want to eliminate all green components you'd simply want to black out the green channel.

If you want to add all the content of the green channel to the blue channel first, you could do that by cutting the green channel out (with black as your background color), then pasting it onto the blue channel and fading the mixing mode of the Paste operation to Screen or possibly Linear Dodge.

More specifically:

1. Set background color to pure black.

2. In the Channels panel, choose the Green channel.

3. Select - All.

4. Edit - Cut.

5. Choose the Blue channel.

6. Edit - Paste.

7. Edit - Fade, choose Screen or Linear Dodge to add the pixel values you just pasted to what was already in the Blue channel.

-Noel

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10. Adrtghhjj,

May 4, 2012 11:35 AM in reply to Noel Carboni

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How do I "black out the green channel"? I'm new at PS but I think this is what I've been looking for.

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11. Noel Carboni,

May 4, 2012 11:35 AM in reply to Adrtghhjj

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I added some steps to the above post while you were responding.

-Noel

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12. Noel Carboni,

May 4, 2012 11:36 AM in reply to Adrtghhjj

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Adrtghhjj wrote:

How do I "black out the green channel"?

Another way is to go into the Channels panel, choose the Green channel, then Image - Adjust - Curves, and drag the white point all the way to black.

-Noel

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13. Adrtghhjj,

May 4, 2012 12:48 PM in reply to Noel Carboni

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Thanks. This has solved the problem.

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14. mantralightroom,

Photoshop General Discussion

How to select a color accurately?

May 4, 2012 1:14 AM

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