How to find the intensity of each pixel of an image?

Consider an image sample.jpg Now I want to count the number of pixels on that image have intensity value larger than 200(white pixels).

If the image contain such pixels above 75% then I want to reject the image. How can I accomplish this in matlab?

[Doug Hull]

What format is the image in? RGB or greyscale? If it is just a greyscale image, it is really just a matrix and you can do any calculations on it like you would any matrix in MATLAB.

[shimul]

Yap I have done this. However thanks

Answer 1

[Image Analyst]

If it's a color image, first convert to a gray image

[rows, columns, numberofColorChannels] = size(originalImage);
if numberofColorChannels > 1
  grayImage = rgb2gray(originalImage);
else
  grayImage  = originalImage;
end

otherwise if it's already gray, you don't need to call rgb2gray(). Then threshold

binaryImage = grayImage >= 200;

Then count

numberOfWhitePixels = sum(binaryImage(:));

Note: MATLAB uses the American spelling of gray, not the English spelling of grey.

[sindhu c]

Hello,i have grayscale image,and i have to find the average of intensity of black pixels(not counting the number of black pixels,but),how do i do it??Please help me.

[Walter Roberson]

blackpixels = grayImage <= SomeThreshold;  %find them
black_average = mean( grayImage(blackpixels) );  %average them

[sindhu c]

ok sir thank you,i will try with it

[sana saleeme]

kindly elaborate above answer.i want to count the intensity values of pixels.

[Image Analyst]

The "count" of the "intensity values" of the pixels will be the same as the count of the pixels, which is simply the number of pixels. I already gave this to you in my original answer. For example you may have these pixel column locations in row 1 be less than 200: 233, 234, 235, 259, 300, 844. That's 6 pixels, so the count is 6.

Then you asked how to find the mean intensity of those. That was also answered by Walter. So if the intensities of the 6 pixels above were 201,202,203,204,205, and 206, the mean would be (201+202+203+204+205+206) / 6 = 203.5

If you want the dark pixels, just flip the > to < like Walter did, and that will count the dark pixels and/or give their mean value.

Now, you're back to asking about count again, which has already been answered.

So, explain what is not yet being answered from us that you need.

[sana saleeme]

image analylst what should i do if i want to count only the black part of an image? and my image is

[sana saleeme]

please please answer it please

[Image Analyst]

Take the histogram and sum up the bins that you consider to be "black".

[sana saleeme]

image analyst after taking histogram how to sum up?please elaborate?

[sana saleeme]

[counts,binLocations] = imhist(d); i use this function.

[sana saleeme]

image analyst please do one favor.can you tell me how i can count all the cells that have black dots in the above image? sir i will be very thankful to you.

[sana saleeme]

is there is any method through which i can remove all those objects that does not contaian black dots?

[Image Analyst]

You should start your own question for this.

[sana saleeme]

will you answer me there?

Answer 2

[Upeka Somaratne]

How can I get the pixel coordinates of the pixels which have intensity value greater than 200? (in matlab)

[shimul]

[rows, cols] = find(yourImage > 200);

considering the image is grayscale.