Reducing colors in photoshop? (making many colours fewer)

[Guest]

Hi! I've been working on some pictures that will be printed on T-shirts. The problem is that I've got alot of different color in the pictures which would result in a very expensive print. What I would want to be able to do is to reduce the colors in the pictures to only 4 specific colors (plus black and white). The colors must be very specific. for an example:  "ff2600". 

To be totally clear: I need the ALL the different types of yellow into be transformed to just one type of yellow.

So my question is am I able to do something like this in photoshop?

I'd be very grateful for some answers!

Thank you!

// Hannes

[Guest]

Save as a GIF and, in the intermediate dialog, under Colors type "4" then select Custom and nominate them using the Color Picker.

[Guest]

Thank you all for great answers! I really appreciate it!

I'll try to look through all your ideas and I'll come back here if I'll run into any trouble:)

Thanks again.

[Reynolds__Mark_]

There is an adjustment layer called POSTERISE, if you choose 4 levels in this, it will seperate your image into 4 average colors. Beneath that adjustment, a LEVELS adjustment will allow you to reassign the tonal values of the image, and interactively see the results while you do it.

These values can then be filled with whichever specific colors you want. Using any image reading selection tool - inluding Color Range, Magic wand, even Paint bucket

[Gyno-jiz]

Posterize will result in x levels per channel. Either way, I think we're all confusing colors and inks.

[Guest]

He wanted exact specific colours not averages!

[Reynolds__Mark_]

And I told him how to get them, in the most versatile way

[Guest]

Reynolds (Mark) wrote:

And I told him how to get them, in the most versatile way

If you say so! 

[Semaphoric]

Posterize would not work, since it acts on each color channel independantly. You wouldn't have to save as a GIF, though. Just change the mode to Indexed Color.

Use the "Custom" palette, with Colors set to 6 (your four inks plus black and white), and "Forced" set to "Black and White". You can edit your palette as desired, and save it for later use. It can be tricky to get the image to look natural doing this, though; you may be better off starting with something like "Local Perceptual", and then switching to Custom to tweak it.

Once you have the image looking the way you want, you can use the Magic Wand to select each of the colors, create new channels, and fill the selected area in them with black. You can then use these alpha channels to make your screens.

[Reynolds__Mark_]

Sigh, I sometimes wonder. Posterize does work. I would have thought its quite obvious that a desaturation (or even better a grayscale channel mix) has to be performed first.

The GIF or indexed color method although it kind of works, just crudely splits the image based on color into 4 values. The division of these tones cannot be controlled. I would hope that its pretty essential to control the quality of that separation, and was trying to show a method that easily allows this.

[Semaphoric]

Here's another way:

Make sure your desired colors are in your swatch palette/panel. Use Select > Color Range to select those colors adjusting the fuzziness as desired.

Save each selection in an alppha channel, naming them appropriately. Tweak them if needed with curves or levels, and then run Threshold on them.

Load each saved selection in turn, and fill the selection on a blank layer, using the corresponding color.