int pixelValue = Color.FromArgb(0, red, green, blue).ToArgb();

This is not very wise, because since the ToArgb() method will return a 32-bit integer in the form AARRGGBB, differences among the pixels on the red channel will account more on the calculated standard deviation than differences on the green channel, and even more than on the blue channel. This leads to some difficulty in setting a threshold for the standard deviation value of the images, because the algorithm may return quite different values for images which are near the blank/not-blank point.

A more meaningful value to the pixelValue variable is:

int pixelValue = red + green + blue / 3;

or

double pixelValue = red + green + blue / 3.0;

This way, differences in the 3 channels are accounted with the same weight on the result. Also, the algorithm’s output becomes much more comprehensive, varying from 0 to 255. Setting a threshold with this modification to the algorithm has proven much easier. The algorithm usually returns a value close to 1 on blank images and above 8 on non-blank images. I am currently using 2 for threshold, with a near perfect accuracy rate.

I know this means we’re interpreting the image as if it were in grayscale, but in my experience it makes no difference.

I have an scanned document with multiple pages and every alternate page is blank.
When I tried to convert each page to image and run the above code still it is showing Isblank has “false”.

How do I overcome the above issue?

Whether tolerance is same for all .tiff files (or) it varies for each page?

For an given multi page scanned document, how do I find the tolerance value?

Any help is highly appreciated.

need your suggestion as to how to put the code that you have given into a project?
I want to do something similar, and scan through a folder, containing thousands of images, and get as output the filename of a blank image.

Has anyone convert this code to VB?

Do I have to use the “Pointer” method or can the code be written without using a Pointer?

Thank you for your Help!
Phil

I’ll keep my eye on this page incase anyone else has a more efficient solution.

ie:
byte bytesPerPixel = (byte)(bitsPerPixel / 8);

if bitsperpixel < 8 the bytersperpixel = 0

and p += bytesPerPixel; is p += 0;

I tried a work around by making in p++ every 8 loops but that didnt work…. (for a 1 bpp bmp)
im a programming n00b.. any ideas?

I’ve added try catch with continue inside:
try
{
count++;

byte blue = p[0];
byte green = p[1];
byte red = p[2];

int pixelValue = Color.FromArgb(0, red, green, blue).ToArgb();
total += pixelValue;
double avg = total / count;
totalVariance += Math.Pow(pixelValue – avg, 2);
stdDev = Math.Sqrt(totalVariance / count);
p += bytesPerPixel;
}
catch
{
continue;
}

seems to have fixed the issue, but I still dont understand why some images will throw an error.

Times: What do you mean changing the hex to dec? all functions really on a byte not decimal value. Can you repost the decimal version?

Thanks