Get rid of one gray w/ photoshop

December 9, 2008 8:32 AM

Easy (probably) photoshop question. I want to remove exactly one shade of gray from a grayscale image; can this be done?

I've got a grayscale image that has a lot of artifactual background noise. The noise is all the same gray value (see the spike on the histogram). Can I knock out that one gray and nothing else? Thanks for any/all help.

posted by sleevener to media & arts (4 comments total)

Select color range? Magic Wand tool?
posted by niles at 8:48 AM on December 9, 2008

I'm no Photoshop expert, so there may be some magic tool I'm unaware of, but my first thought was:

If the noise is all over different areas, you'll probably want to replace the dots with an appropriate shade, rather than just a different shade.
If they're all single pixel dots, you could do this by using the Magic Wand to select one dot, then going to Select / Similar to select them all. Move the selection one pixel to the side using the arrow keys, then copy and paste those adjacent pixels onto a new layer, and move the layer back over the noisy pixels to cover them.

Hope that makes sense.
posted by lucidium at 8:59 AM on December 9, 2008

I would use Image > Adjustments > Replace Color (I'm looking at Adobe CS3 but this feature has been in for several versions, at least since 6, which is when I started using Photoshop heavily.)

Select the shade of gray with the eyedropper and change the fuzziness to 1, then tweak the saturation slider until it disappears into the background.

If you want different color values in different parts of the image, you can use the marquee or lasso select tools to restrict the area of the "replace color" function and then repeat the operation.
posted by camcgee at 9:01 AM on December 9, 2008

Got it! Thanks all.
posted by sleevener at 9:03 AM on December 9, 2008