On Mon, January 26, 2009 12:52 am, Wolfgang Hugemann wrote:

> JPEG-Colorspace: 2
> JPEG-Sampling-factors: 2x2,1x1,1x1
>
> I bet that JPEG Colorspace no. 2 is RGB (?). But I am really confused by
> the sampling factors, which I attribute to Y, Cr, Cb. Now, Y should not
> be sub-sampled at all and Cr and Cb should be subsampled either by the
> factor 2 (when counting in just one direction) or 4 (when counting the
> amount of pixels).
>
> So what does the above line this really tell us? I could not find any
> detailed explanation for the output of 'identify'.

I've always read that as:

For every 2x2 set of Y samples, there's a 1x1 set of Cr and Cb sample(s).
In other words, just what you'd expected - Cb and Cr are sampled at a rate
1/4 (in 2d) of the Y samples.

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