Cleaning up Graphics for Dummies

November 6, 2020 6:12 PM

I'm downloading images from the Internet Archieve Book Images Flickr page for a personal zine project. These are scans of old books so they have yellow backgrounds such as this and like this one. I am looking for an easy, cheap, not-to-technical way of making these images black and white again (instead of yellow and black) so they will photocopy well. A chromebook solution would be preferable.
posted by vespabelle to Technology (4 answers total)

You could open them up in Gimp or Photoshop and index it to two colors, then replace the yellow with white (or transparent, as needed).
posted by janell at 7:13 PM on November 6, 2020 [1 favorite]

I have no idea what kind of cheap or free image editors are available for a chrome book (I assume GIMP is), but every modern image editor I've ever used has a Levels control and the ability to turn a color image into greyscale. First, turn it into greyscale using whatever method your software allows (it's probably just a command in a menu). Then, change the levels. There should be a slider for blacks on the left and slider for white on the right. Move the white slider further to the left to brighten it up. This should turn the light grey (which used to be yellow) to white. You may need to adjust the middle slider (which handles grey) to make up for the fact that the entire image is now lighter.
posted by jonathanhughes at 7:26 PM on November 6, 2020 [2 favorites]

If you know anyone with Photoshop, they can make a Bulk Photoshop Action that will run the same 2 image adjustments (brightness, then desaturate) that can be applied to a whole folder of images with one click.

If you want to do them yourself, and Gimp isn't available on your chromebook, you can apply jonathanhughes instructions to this free online clone of photoshop: https://www.photopea.com/
(Image > Adjustments > Hue / Saturation
Image > Adjustments > Brightness/Contrast)
posted by weewooweewoo at 3:05 AM on November 7, 2020

If you use GIMP (should work on Chromebook as GIMP Portable), the following two steps probably suffice:

1. From the menu, "Colours" > "Desaturate" > "Desaturate...". The default setting should mostly work. Apply that and the image would look like it has a hazy grey background
2. Again "Colours" > "Brightness and Contrast". Turn up the Contrast and turn down the Brightness until the preview looks right.

The edited images can be then saved as JPEG or PNG using "File" > "Export As". Once exported as new files, the edited images can be closed. The app will ask if you want to discard/save the edits, referring to these edits on the original file. You can safely discard them because the edited files are already export.

If it is desirable to replace the (now mostly white) background into transparency, there's Colour to Alpha.
posted by runcifex at 3:30 AM on November 7, 2020