Sizing question--Please help


Carol Steele

I can see this might be beneficial if you are resizing Jpeg files. This is because the JPEG algorithm looks at blocks of 64 pixels (8x8) and abrupt changes show up at the interface lines (which is why areas of smooth gradation can start to look 'blocky' in jpeg compressed files. However, AFAIK, it has no bearing on resampling TIFF's or similar formats.
Feb 2, 2005
Real Name
Hi again Paul,

Here is my explanation of how downsizing can blur an image:

Chris in another place said:
Imagine a six by one pixel picture that is made of two white pixels, two black pixels followed by two more white pixels. The black region in the center is has very sharp edges:

    W W B B W W

If this is then resized to five pixels wide, the central black region becomes three pixels wide, with only the center pixel completely black, with gray pixels along the edge:

     W G B G W

and the image is less sharp.
This doesn't explain why 16ths is a magic number though. Downsizing by an even number though does seem as if there will be less blending to gray, at least in the example I've shown. You've already done a lot of work, searching down that Lab color thing, so you can leave this one alone if you want. It seems that there should be some documentation out there to support a rigorous downsizing scheme, and I'll keep an eye open for it.

Not today though, I'm off on a task.
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