changing the pixel color in an image

I have a raster image and I have the coordinates of the shown point. I need to change the colour of the area occupied by the image(i.e. the black pixels) in the two perpendiculars drawn from the same point(along x and y-axis). Is there any function that I can use?

[Jan]

I do not understand the question. What is "the coloured area"? Do you mean the black pixels which are under the green bars? Or inside the rectangle built by the green bars?

[Busy Bee]

after changing the colour of the black pixels inside the rectangle to yellow, i needed to know the total number of yellow pixels. But now i get that I can do it directly using the find command.

Answer 1

[Image Analyst]

Convert your calibrated x,y into rows and columns, then make two masks and AND them together and use sum() to count pixels

yellowMask = rectangleMask & ~blackPolygonMask;
numYellowPixels = sum(yellowMask(:))