I want to mask different type of RBC with different color. After selecting same type of RBCs using Fuzzy Selection Tool (and Remove Holes option) , I used Bucket tools to FIll whole selection. But I'm getting some part of selection not completely colored. Is there something wrong in the steps I'm following?
Check these images
Selection Region before using Bucket tool
Selection Region after using Bucket tool (Note the partially filled region)

  • Seems a bit counterproductive to select and then bucket fill
    – joojaa
    Jul 12, 2020 at 14:38
  • Using any "bucket fill" in 99.9% of apps is among the worst methods to fill an area with color.
    – Scott
    Jul 12, 2020 at 17:33
  • I believe selection is necessary because some cells have white holes in it(check the 1st image) and fill with bucket will leave the hole unfilled. Jul 13, 2020 at 9:15

1 Answer 1


There's no need to make a selection first. Change the Threshold slider in the tool options until you get the desired result. Also you appeat to have an old version of GIMP. Perhaps consider upgrading to a more recent version if you want this functionality.

Example in GIMP 2.10.18

enter image description here

  • This method didnt work on some cells because of white patches inside those cells. and those patches have almost same color as BG. If I increase threshold too much, BG also gets filled with color. check this link. imgur.com/t5aea1G Jul 13, 2020 at 10:03
  • @AbinashDash Then you could try increasing the contrast a little, or changing the "Fill by" option to the red, green or blue channels. You may have to experiment with the settings. All colour selection tools rely on at least some contrast in the image between background and subject. There's no way round this if you don't have adequate contrast. If there are white holes in some, then you'd need to select the inner part separately perhaps.
    – Billy Kerr
    Jul 13, 2020 at 10:13
  • I'll try changing contrast a little bit and fill again. Jul 13, 2020 at 10:16
  • Can you give me any hint on why some regions were not completely red inside my selection? Fill selection should ideally fill whole region with same color. isn't it? Jul 13, 2020 at 10:21
  • @AbinashDash - because if the cells are white inside, then the selection tool doesn't know it's supposed to be one solid blob. It only looks for the colour which is sampled by the tool. One other possible workaround is to switch to the Paint Brush to manually paint in a hole.
    – Billy Kerr
    Jul 13, 2020 at 10:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.