how to whiten the white parts and blacken the black parts of a scanned image in MatLab or photoshop

Question

I have a scanned image, scanned from printed word (docx) file. I want the scanned image to be looked like the original word file i.e. to remove noise and enhancement. i.e. to fully whiten the white parts and fully blacken the black parts without changing colorful parts on the fileenter image description here

Answer 1

There are a number of ways you could approach this. The simplest would be to apply a levels filter with the black point raised a bit and the white point lowered a bit. This can be done to all 3 color channels or selectively to a subset. Since you're going for creating pure black and white and there's no color cast on the image, I would apply the same settings to all 3 color channels. It works like this:

destVal = (srcVal - blackPt) + srcVal / (whitePt - blackPt);

This will slightly change the colored parts of the image, probably resulting in making them slightly more or less saturated.

I tried this in a photo editing app and was disappointed with the results. I was able to remove most of the noise by bringing the white point down to about 66%. However, the logo in the upper left is so wispy that it also ended up turning it very white. The black point didn't really need to be moved.

I think you're going to have a tough time with that logo. You could isolate it from your other changes, though, and that might help. A simple circular area around it where you just ignore any processing would probably do the trick.

But I got to thinking - this was made with Word. Do you have a copy of Word? It probably wouldn't be too difficult to put together a layout that's nearly identical. It still wouldn't help with the logo. But what you could do is layout the text the same and export it to a PDF or other image format. (Or if you can find the original template, just use it directly.) Then you could write some code to process your scanned copy and wherever a pixel is grayscale (red = green = blue), use the corresponding pixel from the version you made, otherwise use the pixels from the scan. That would get you all the stamps and signatures, while having the text nice and sharp. Perhaps you could even find the organization's logo online. In fact, Wikipedia even has a copy of their logo.

You'd probably need to have some sort of threshold for the grayscale because some pixels might be close but have a slight color cast. One option might be something like this:

if ((fabs(red - green) < threshold) && (fabs(red - blue) < threshold))
{
    destVal = recreationVal; // The output is the same as the copy you made manually
}
else
{
    destVal = scannedVal; // The output is the same as the scan
}

You may find this eats away at some of the colored marks, so you could do a second pass over the output where any pixel that's adjacent to a colored pixel brings in the corresponding pixel from the original scan.