Legacy ImageMagick Discussions Archive

Simply adding +0 to the crop geometry fixed it but I don't understand why. I guess it's to do with the bizarre default behaviour generating a series.

I'm using the following command to crop the centre portion of an image and then resize the result. convert -gravity center -crop x450 -thumbnail 192x This completely fails to work and is very frustrating. It takes the first 450 rows from (0,0) instead of from the center and it doesn't bother to thum...

Or does the quality decrease through lossy re-encode?

NicolasRobidoux wrote:Use 1x1.

I actually tried that but I got the same result as if I hadn't specified the sampling factor option at all so I thought it must be invalid. The only value that I tried which changed the output was 2x1 which resulted in a file size reduction.

How do I disable chroma subsampling with ImageMagick?

Oh, OK. That's cool, I guess. I wasn't trying to take away your livelihood.

Why might someone turn off chroma subsampling?

Hi, I only know a little about the JPEG format but I thought that JPEGs are subdivided into "blocks" at a low level. Is it therefore the case that if you want to generate as small a thumbnail image as possible you should select image dimensions that are divisible by this block size? If so ...

Is there a way to calculate a hash of the decoded image information only? That is, for two identical images with different metadata, the hash will be the same.