counting pixels of certain irregularly spaced area in image

how can we count the total pixels in the sector shaped region( total means sum of red,yellow,bluish and white pixels in the sector). The problem i am facing is finding number of white pixels inside sector. When i run a loop to scan for white pixels in sector, program also scans the white pixels in the tiny white squares along the border of rectangle. Is There any other way to find the total pixels in sector. Below is if else loop i am using.Thanks.

if(red threshold) red=red+1; elif(yellow threshold) yellow= yellow+1; elif(bluish threshold) bluish = bluish +1 else(white threshsold) white= white+1; else black = black +1;

[sandeep]

Please find image attached as test S-scan.BMP Don't worry about the red and blue lines in image. They can be removed in View Menu of my software that makes image. But it can't remove small white squares.

[sandeep]

attached is the image.