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Re: filmscanners: On A More Positive Note




--- tflash <tflash@earthlink.net> wrote:
> The blue channel of the pad lock image shows what
> appears to be jpeg
> artifacts, but none of the other channels do. I know
> the blue channel is
> typically the noisiest channel of a scan, but I
> forget why. Isn't it because
> the CCD elements are least sensitive to blue light?
> If so that is a hardware
> thing. But jpeg is a software thing, so why would it
> also show up
> predominantly in the blue channel? Is that typical
> of jpegs, or was it just
> a fluke or coincidence here?

Actually, you see the jpeg artifacts clearly in all
channels and the picture itself. Nevertheless, it is
the clearest in the blue channel, followed by the red
with green showing the least artifacts. The reason why
green probably shows the least artifacts is because
JPEG stores the data in YCbCr with Cb and Cr
downsampled by 2 (-> 1/4 the data points compared to
Y). The reason why you see more artifact in the blue
channel then the red channel might be what you have
mentioned in your message. Not really sure about that,
though.

Robert 

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