Wikipedia:Reference desk/Archives/Computing/2021 August 25

= August 25 =

What causes graying color over text in images?
I have 2 image files with black and white text, pasted onto Microsoft Word. Then, Word is save as'd to a PDF file. Only problem is, 1 of the image has clear cut white background around the text, but the other image, has graying color background behind the text. But they looked the same on Word. I later tried to create a new Word file and put them both in at the same time to save as to PDF file, still the same. On Paint, and Word, the image looks clean. Now, you would think 1 of the image was a .jpg, but both were .png. So I don't know what caused it. Sometimes if I save a image text on Paint, it immediately causes the background to be messy-gray around the text, but for these cases, the image were clean in Paint and Word, but not in .pdf. 67.165.185.178 (talk) 05:40, 25 August 2021 (UTC).


 * Are you sure the background is white in both figures? If I recall correctly PNG allows for transparent backgrounds. I am not sure but if that is then saved as PDF (which compresses the figure again), it might explain the edges. Also, in Paint there is (was??) no transparent background, so an image with transparent background would edited as bitmap and merged with the white default colour, with the same effect. Rmvandijk (talk) 07:01, 25 August 2021 (UTC)


 * This may be due to alpha transparency. If you have the Netpbm library installed, something on the command line like
 * may get rid of the problem. (I have not tested this since I had no png grayscale image with alpha transparency readily available.) Possibly there are more direct methods of making the png image opaque (setting α equal to 1). Here is an online tool that is supposed to do the job. If you have Photoshop, saving the image using Photoshop as a .jpg file reportedly makes it opaque with a white background by default. --Lambiam 08:26, 25 August 2021 (UTC)
 * may get rid of the problem. (I have not tested this since I had no png grayscale image with alpha transparency readily available.) Possibly there are more direct methods of making the png image opaque (setting α equal to 1). Here is an online tool that is supposed to do the job. If you have Photoshop, saving the image using Photoshop as a .jpg file reportedly makes it opaque with a white background by default. --Lambiam 08:26, 25 August 2021 (UTC)


 * Your description is a little vague - when you talk about the grey area around the text, are you referring to aliasing? Our article gets quite technical, but what I mean is: does it appear that the text on the one image has been kind of blurred into the background so that the hard edges get smudged? There are many sources of that, which may come down to how the images were created, but one of the easiest pitfalls is careless re-sizing. For example, if you screen-shot this text and pasted it elsewhere it would look okay, but re-sizing the image to make the words bigger could introduce the artifacts you describe. It could be as simple as the two images having been re-sized differing amounts. Matt Deres (talk) 20:21, 25 August 2021 (UTC)
 * Hm no, text is not blurred, only the background of the text blurs into a light-grayish color. 67.165.185.178 (talk) 01:47, 26 August 2021 (UTC).