Hi gurus
I?m trying to clean up some engineering drawings that have been saved in bitmap / tiff format. When I open the files I convert the image to grayscale so that I can erase marks, add text etc. No matter what I try however I can?t manage to adjust the levels. This is really important as the drawings are mostly old and faded. Photoshop seems to go through the motions on screen but when I try to accept the changes it reverts to the original levels. It?s the same using brightness/contrast, levels or curves. I?ve tried saving and re-opening the image as tiff, psd and jpg. I?ve tried new duplicate layers as well as cutting and pasting to new ?clean? layer. I?ve even tried converting from 8-bit to 16-bit.
It was suggested that the tiff format might have something to do with it but I have no control over that and besides, surely Photoshop can manipulate all image types. Incidentally I have no trouble working with images and other line art, only these engineering drawings.
I?m sure there must be a simple explanation but so far no one has been able to help me find it. Anyone out there got some ideas?
jw
Problems with levels 
Linear Mode
