Lourens Veen wrote: > > Peter wrote: > > > > I found how to change the comment in a JPEG when I "save as", and how to > > change the default for the "save as", but I could not find how to view > > the comment in an input file or edit the comment prior to performing a > > normal save. > > I think this is built in the save routines, I don't think there is a > separate comment attached to an image. It sounds like a useful feature > to me though. It appears to be the right spot to store a copyright notice and the alt= information, especially for the blind. > > > I found how to change the compression level in a JPEG when I "save as" > > but could not find out how to view or change the compression level prior > > to a normal save. I think, from what I see of the JPEG format, the > > compression level is not stored anywhere but it could be indicated by > > displaying something like the colour range (I do not remember the JPEG > > term, it is the part that indicates the 24,000,000 colours are squashed > > down to an actual range of n colours. > > There is no such thing. Indeed, JPEG uses vector quantisation, but it's > a little bit more complicated than just making a palette. The encoder > has a q factor (ranging from 0.0 to 1.0 in Gimp) which determines the > quality, but other than that 0.0 is worst and 1.0 is best, it's > undefined and may vary in meaning from encoder to encoder. I think that > if you Save As with a certain q factor, and the save the same file again > with Save, you get the same q factor again. If you want to save with a > different q factor, use Save As. > > > I also could not find out how to change the default JPEG quality setting > > from .75 to 1 and only discovered the setting when I found a few files > > were damaged after minor adjustments. > > "damaged". You mean they were saved at a lower quality? Please note that > a q factor of 1 does not mean lossless compression. There is indeed a > lossless JPEG mode, which is prediction based and totally different from > the lossy DCT and vector quantisation scheme that is used in Gimp. AFAIK > Gimp cannot save lossless JPG's. If you want to save your files > losslessly then I recommend PNG, it has good compression, is an open > standard and works with web browsers. I will try PNG (I already use ping a lot so PNG should be easy to remember.). Some cameras, like the Nikon Coolpix, feature a lossless mode and some software has a 100% quality type setting, where I thought it turned off compression, but did not know there were several types of compression. In the save as, there is a DCT method that says it is a trade off between speed and quality. On an 800 MHz AMD chip, speed does not seem to be a problem so which of the three settings gives the best quality? > > > Which leads to the next thing. If I start with a JPEG that has zero > > compression then edit the file then save as a jpeg with 25% compression, > > I see the change image from editing but not after compression. Is it > > possible to view the file as saved to disk, without having to close the > > file then open the saved file? > > Yes, when you save it there is checkbox "preview in image window". Make > sure it's checked, and watch the image window. Note that a q factor of > 0.75 does not mean 75% filesize or 75% of the quality. It is a > meaningless number. I will try that. > > > I am looking forward to replacing some more proprietary software with > > open source and Gimp is 98% of what I need for image editing. > > Good! Feel free to ask. > > Lourens
