Color Replace

How can I replace a certain color (background color) with something else (for example white). I'm editing a greyscale picture and I want to replace all the grayish white with pure white. How can I accomplish this?

BTW I'm using Photoshop 6

Your best results will happen if you make an accurate selection of the areas you want to change.

Then, you could use Selective Color to yank to component tones out of the light gray areas. It may have to apply the changes a couple of times, but that should work.

This is only one way to do it, but without seeing the image, it's kind of hard to determine whether this would be the best way to go.

No matter what, though, it would be a good idea to isolate the area you want to change.