How can I select a single color within an image?

Question

How would one pick or select all of a single color within Photoshop, Paint.NET, or The Gimp?

The objective is to edit everything with that color afterwards, such as by brushing over it with another color. So if I were to select a certain red hue of an apple, then brushed it over with pink, only all of the parts of the apple with that red color would then be pink. I could use the magic wand tool, but don't know if there's something that can scan the image for every pixel with that color.

Answer 1

Gimp - Select by Color

In Gimp we have the Select by Color tool (Shift+O) to allow a selection based on image color.

Select by Color - Threshold 0

By selecting a color difference threshold of 0 we will select only parts of the image with exactly the same color value (below shown for white):

^{Image Source: Wikimedia}

Select by Color - Threshold 50

To select similar colors we need to increase the threshold, in the example below light green with a threshold of 50 was selected. While keeping the left mouse button pressed on selecting we can adjust this threshold visually while dragging the mouse pointer.

Answer 2

This is a vague question so I'm just going to answer it with what I've used before.

In Photoshop:

You would use the eyedropper tool shortcut I.

In Gimp:

You would use the color picker tool shortcut O.

In Paint:

Also called the Color Picker Tool

Imagemagick command line:

convert <image> -unique-colors -depth 8 txt:- > output.txt

Imagemagick PHP:

ImagickPixel Imagick::getImagePixelColor ( int $x , int $y )

jQuery/JavaScript:

• Color Thief: The documentation for it is bad but there project is solid.
• palette: Very simple tool.

More PHP:

• ColorPalette: Returns an array of all the colors in hex .
• Color Thief in PHP: Same as the jQuery one but just written in PHP.

Answer 3

To select a color, the Photoshop approach is to use Select > Color Range.... To positively select just a single color, either turn off Localized Color Groups or set the Range slider to 100%.

If your color is very well-defined and you don't need an anti-aliased or soft-edged selection, you can use the Magic Wand tool. Set the sample size (which you have to do via the Eyedropper tool in earlier versions of Photoshop) to 3x3 or 5x5 average, and click on the color you're trying to select.

If all you want to do is sample the color, then the alternatives Gramps outlined are correct, although I would again suggest you set the sample size to something larger than a single pixel if the image is jpeg compressed.

Answer 4

Photoshop

(the principle should be the same in other programmes)

I might have misunderstood, but you are trying to select all fields of one specific colour in an image?

In photoshop:

use the magic wand tool:

Select an area with the colour you want, fiddle with the tolerance depending on your image:

Right-click on the area you have selected, and choose similar from the menu: