I am a new user to GIMP and am trying to figure out a way to clean up some noisy microfiche scans. All I need is for the scans to be readable enough so that my OCR program will work on them. The microfiche was in very bad shape and the readers were quite old as well, so the scanned copy of the text was the best I could get after much fiddling around. Just getting a legible copy was a feat. I have attached one image to this message. Text in bold can be recognized through OCR but regular text just seems to blend in with all the dust and speckles.
I was advised by my PDF support person to export the PDF into an image format, and run the image through image manipulation software to lighten the background without altering text. However, in GIMP 2.8, the layers dialog box does not list "background" as a layer option. This was perplexing because when I searched the the web for help using GIMP to lighten the background of an image, several different sites said that you can choose "background" as a layer.
I tried opening the image in layers, used the stack option to choose the bottom image, and fiddled around with various settings, but no visible changes appeared. The only thing I was able to do was to work on the top layer, which changed both text and background, which ended up making the text too light and without enough contrast to be useful. Is there a way to isolate the background, leaving the text in tact? I don't need these to look great by any means - just legible enough so that the OCR program can work. It may be impossible, but I did want to find out.
Many many thanks!