Question posted in 
I have scanned images with alpha channel that I need to compress. The images are drawings. Unfortunately their creation process creates random variation in color that compress poorly in PNG or even cause negative compression.
If I run filters over the data, I wipe out the text.
If I could split out all the pixels that are approximately a specific color into a separate layer, I could run filters without affecting the text.
There are four distinct colors I would like to split out.
The source image is indexed so there are not a lot of variation that needs to be split out.
Is this possible in Photoshop? If so, how?
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I have not seen the format for a human readable color table. That would make things a lot easier. I have created some within photoshop and it is a PITA.
I was thinking about doing this manually at first then possibly automating it.
I have tried the magic want toll but I cannot get it to distinguish colors well. For example, I have purples and black. To get the thing to select all the purples, it grabs the blacks as well.
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Answers
The best thing I could come up with was MAGIC WAND and disable the continuous setting. Cut and Paste Special to a new layer.
You can Scan image with Photoshop File > Import > WIA Support select your printer/Scanner and then scan your picture its come in actual color which you want and then you can compress its not distort your color
I would preferred to select Polygon lasso or Magnetic lasso tool to select specific area.
Otherwise you select the command Select | Color Range and Select color with eyedropper tool
Best way to select all of a certain colour is to go to Select>Color Range
then select white with the eyedropper tool, this way it selects everything with the white value more accurately than manually with he magic tool, it gets all the little things you may miss. then use that to cut/paste into a new layer with ctrl+shift+v to put paste it in place 🙂