2004.05.28 14:35 "Re: [Tiff] Tiff JPEG compression quality factor", by Bob Friesenhahn

I'm using the libtiff v3.6.1 and I can save a tiff file with Jpeg compression and quality factor 80, but when i try to open it, the jpeg quality factor pseudotag has a value of 75. I guess I am doing something wrong, > because I assume that I can read the Jpeg quality factor written in advance. > Is that correct?

The notion of JPEG "quality factor" is specific to the IJG JPEG library. There is no quality factor saved to the image. However, as it turns out, the parameters used when saving the JPEG may be estimated when the image is read.

GraphicsMagick 1.1 includes some code which accurately estimates the IJG JPEG quality factor and sampling factors when a JPEG is read and allows you to save using the original parameters. However, I believe that complete support is implemented for JPEG files only and not for JPEG in TIFF (but I could be wrong). I have not tested JPEG in TIFF to see if the parameters are recorded and saved.

Bob

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Bob Friesenhahn
bfriesen@simple.dallas.tx.us
http://www.simplesystems.org/users/bfriesen