Calculating the number of pixels inside a freehand region.

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Salman 2014-7-1

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评论： Image Analyst 2022-4-25

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.

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Spandan Tiwari 2014-7-11

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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
bw = createMask(f);
outI = bw.*I;
numPixelsInsideRegion = sum(outI(:))

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Rukevwe Rim-Rukeh 2022-4-25

can you loop the freehand command, so you dont have to continously draw the area

Image Analyst 2022-4-25

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Sure. Just put it in a loop and OR it into the "master" binary image

finalMask = false(rows, columns)
for k = 1 : 10
    thisMask = (however you get it, like with drawfreehand());
    finalMask = finalMask | thisMask;
end

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Image Analyst 2014-7-1

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freehand_masking_demo.m

This is exactly what my freehand drawing demo does. See attached.

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Salman 2014-7-2

编辑：Salman 2014-7-2

This is the image

and let's say that this is the free hand region that I select

As you can see that the image contains only two colors, i.e. black and white. Now what I want is, to find the total number of white pixels inside the freehand region that I draw and also the number of black pixels inside the freehand region.

I'll be grateful for any help.

P.S. I'm a newbie to image processing.

Image Analyst 2022-4-25

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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);
newMask = originalBinaryImage & insideShape;
pixelCount = nnz(newMask)

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