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Explain This For Me...


zeitgeist

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The way I understand it is that when an image is compressed, or, downsized from a high resolution to a lower resolution, i.e. from 300 dpi to 72 dpi, the way it's done sometimes is to interpolate.

 

I think interpolate in this sense means if there are a large amount of pixels that are almost the same in color, brightness, etc, then rather than describe each one, in the file, it is acceptable to describe a bunch of them as being the same.

 

So if there are 1,000 pixels that are all nearly the same shade of grey, instead of doing something like this: 0001=grey10.01%, 0002=grey10.02%, 0003=grey10.32% and so on for the thousand, you can just say something like 1,000 pixels=10.22%. This goes for all the various parameters that describe the pixel.

 

Now from Mr Wiki - "In image processing, bicubic interpolation is often chosen over bilinear interpolation or nearest neighbor in image resampling, when speed is not an issue. In contrast to bilinear interpolation, which only takes 4 pixels (2x2) into account, bicubic interpolation also considers the 16 pixels around it (for a total of 4x4 pixels) while computing an average. Images resampled with bicubic interpolation are smoother and have fewer interpolation artifacts."

I take all this to mean, when bicubic does it's stuff, it evaluates 16 pixels around the one it's describing, instead of 4 for bilinear. This makes it more accurate and thereto better. When you get 2 black ones next to 2 white ones in a 4 pixel sample, you might get 50% grey for example. But if 16 were looked at you might find that there's still only 2 black ones and 14 white ones which would result in a paler shade of grey and this would look more like the original. The human eye/brain compensates this way all the time. Just look at a newspaper photograph with a magnifying glass, it's all just a mix of dots combining to give the appearance of solid colors and shapes.

 

I think I've got that right, but then, as I get older, I finding lots of things that aren't true anymore. Like, you can trust bankers, or borrowing money is a good thing. But I rant.

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