how can i calculate the area of ​​the white part of this image?

[Walter Roberson]

What do you define as "white" for this purpose? All of that image is white, with varying intensities (the black part is "white with intensity 0")

[Image Analyst]

Didn't we do this already? That image looks familiar. I believe I remember telling you to get a binary image

binaryImage = grayImage > lowThreshold & grayImage <= highThreshold;

Then count the number of pixels in the mask with nnz(), bwarea(), or sum():

numberOfPixels = nnz(binaryImage);

[Inês]

I mean white with intensity 1.

It is the first time that i make this question. Thank you for answer me

Answer 1

[Meg Noah]

Here are two ways:

[imarray,cmap] = imread('01NT.bmp');
im225 = zeros(size(imarray));
im255 = zeros(size(imarray));
im225(imarray==225) = 1;
im255(imarray==255) = 1;
fprintf(1,'Number of white pixels == 255: %d\n',sum(im255(:)));
fprintf(1,'Number of grey pixels == 225: %d\n',sum(im225(:)));

fprintf(1,'\nBlob-by-blob area of white (value=255)\n');
a = bwlabel(im255,8);
stats = regionprops(a,im255,'All');
totalArea = 0;
for iblob = 1:length(stats)
    fprintf(1,'Area(%d) = %d\n',iblob,stats(iblob).Area);
    totalArea = totalArea + stats(iblob).Area;
end
fprintf(1,'Number of pixels == 255 (white): %d\n\n',totalArea);

fprintf(1,'\nBlob-by-blob area of grey (value=225)\n');
a = bwlabel(im225,8);
stats = regionprops(a,im255,'All');
totalArea = 0;
for iblob = 1:length(stats)
    fprintf(1,'Area(%d) = %d\n',iblob,stats(iblob).Area);
    totalArea = totalArea + stats(iblob).Area;
end
fprintf(1,'Number of pixels == 255 (grey): %d\n\n',totalArea);

[Inês]

It was a good help, thank you!

[Meg Noah]

You're quite welcome.You can do unique(imarray(:)) or histogram(imarray(:)) to find what the values are in the image.