How to segment black pixels from a colour image?

I have a colour image. From this image I have to remove the black circles and black symbols from it. How can I do it?

Answer 1

[Stalin Samuel]

remove pixels in an image

Answer 2

[DGM]

If you want to clean up that image, start by deleting it and getting the original image before it was reduced to a microscopic JPG pixel salad.

% read the garbage image
inpict = imread('if_you_want_to_ruin_your_image_save_it_as.jpeg');

% 75% of chroma information has been discarded
% so H, S are mostly useless for any task selecting small features
% just use luma alone to select the region
mask = rgb2gray(inpict)<110;

% get rid of single-pixel speckles
mask = bwareaopen(mask,2);

% show the mask
imshow(mask,'border','tight')

% inpaint the masked region
outpict = inpict;
for c = 1:size(inpict,3)
    outpict(:,:,c) = regionfill(inpict(:,:,c),mask);
end

% show the image
imshow(outpict,'border','tight')

But wait! Now there's a 10px-wide halo of garbage all around where the black lines were! Surprise! Those were there to begin with.

So what are the lessons?

• If you can create a mask to define a region of an image that you want to inpaint based on its immediate surroundings, you can use regionfill().
• Don't save images as JPG unless you understand the amount of information you're throwing away. Generally, don't use JPG for any technical purposes where images need to be reprocessed.