# Calculating the number of pixels inside a freehand region.

22 views (last 30 days)
Salman on 1 Jul 2014
Commented: Image Analyst on 25 Apr 2022
I have a binary image, what I want to do is select a freehand region and then find out the total number of white and black pixels inside that region.

Spandan Tiwari on 11 Jul 2014
Since you are already using imfreehand, you can use the method named createMask available in the imfreehand object to rasterize the marked region into a binary image. Then you can just use logical AND to combine the binary image with your original image and sum over all the pixels in the image to get the desired count. I think the code would look something as follows. Say your image is called I.
figure, imshow(I)
f = imfreehand;
% Then draw the region using imfreehand tool
outI = bw.*I;
numPixelsInsideRegion = sum(outI(:))
Image Analyst on 25 Apr 2022
Sure. Just put it in a loop and OR it into the "master" binary image
for k = 1 : 10
thisMask = (however you get it, like with drawfreehand());
end

Image Analyst on 1 Jul 2014
This is exactly what my freehand drawing demo does. See attached.
Image Analyst on 25 Apr 2022
See my demo to get the coordinates of the hand-drawn shape. Let's call them x, y, so first create a mask with poly2mask, then use nnz()
[imageRows, imageColumns = size(originalBinaryImage);
insideShape = poly2mask(x, y, imageRows, imageColumns);

### Categories

Find more on ROI-Based Processing in Help Center and File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!