Re: [Gimp-user] optimizing image for internet using GiMP
What would happen to a jpeg image if I open it up and save it at 75% quality. Reopen the image and save it again at 75%? Would there be loss to quality? Seems like it would. Once I opened a picture I saved at 75% before and saved it at 100%. The file size increased. I don't understand that. There are times when I want to open a jpeg just to resize the picture, and then save it again - but I don't want to lose any more quality - and I don't want to increase the file size compared to what it was before. How do I go about handeling this? Also, where can I find documentation on the web where I can lern all about jpeg? Thanks in advance. On Wednesday 04 April 2001 19:13, you wrote: Rupert - An indexed image can contain any number of colors (3, 7, 21, 86, . . .) up to the maximum limit of 256. In brief: GIF is a simple indexed format, one byte per pixel, which limits the total number of colors to 256 maximum. It will allow for on/off transparency; one color can be called transparent. JPEG allows for millions of colors (3 bytes per pixel, actually, one each for Red, Green, and Blue), but its compression scheme is lossy, trading fine color detail for reduced size. The usual rule of thumb is GIF for line art and pictures with large areas of a constant color, JPEG for images with lots of detail such as photographs. Nothing really beats loading an image into the Gimp and just playing with it. There's always new stuff to be discovered. -- Rick Rosinski http://rickrosinski.com [EMAIL PROTECTED] ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] optimizing image for internet using GiMP
Hi Rick - Can't answer most of your questions, but I do have one suggestion. When dealing with existing jpegs, or graphics that you work with in Gimp and then convert to jpegs, save a "master" copy (as RGB) in .xcf, Gimp's native format. This way you preserve all of the original quality. Then if if you have to make any additional changes, you can go back to your "master" copy and work with it. ... of course, I use Gimp at work where I've got enough memory to store two of everything ;-) Teri Ward Seattle What would happen to a jpeg image if I open it up and save it at 75% quality. Reopen the image and save it again at 75%? Would there be loss to quality? Seems like it would. Once I opened a picture I saved at 75% before and saved it at 100%. The file size increased. I don't understand that. There are times when I want to open a jpeg just to resize the picture, and then save it again - but I don't want to lose any more quality - and I don't want to increase the file size compared to what it was before. How do I go about handeling this? Also, where can I find documentation on the web where I can lern all about jpeg? Thanks in advance. ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
[Gimp-user] Re: Re: Altering comment in jpegs
I just tried out opening a jpeg with a text editor (vim), and changing the comment manually. This works fine if you make the new comment the same length as the old one. If the new comment is longer, a warning is issued when opening about extraneous bytes, and if the new comment is smaller it doesn't open. This can be fixed by opening with a hex editor, and changing the byte before the comment: xxd myfile.jpg myfile.hex change the line: 010: 0048 fffe 0007 4865 6c6c 6fff db00 .H..Hello... to: 010: 0048 fffe 0004 4865 6c6c 6fff db00 .H..Hello... convert back to binary: xxd -r myfile.hex myfile.jpg Then change "Hello" to "Hi" with a text editor like vim. And I figured that out without even looking at the documentation! I bet it would only take a little C to make an automated jpeg comment changer. Oh, and upon some looking around, there's one right on my system: wrjpgcom. So read the man page on it and see if that's what you want. -James Smaby ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
Re: [Gimp-user] Re: Re: Altering comment in jpegs
Thanks, James. I found wrjpgcom On Friday 06 April 2001 19:56, you wrote: I just tried out opening a jpeg with a text editor (vim), and changing the comment manually. This works fine if you make the new comment the same length as the old one. If the new comment is longer, a warning is issued when opening about extraneous bytes, and if the new comment is smaller it doesn't open. This can be fixed by opening with a hex editor, and changing the byte before the comment: xxd myfile.jpg myfile.hex change the line: 010: 0048 fffe 0007 4865 6c6c 6fff db00 .H..Hello... to: 010: 0048 fffe 0004 4865 6c6c 6fff db00 .H..Hello... convert back to binary: xxd -r myfile.hex myfile.jpg Then change "Hello" to "Hi" with a text editor like vim. And I figured that out without even looking at the documentation! I bet it would only take a little C to make an automated jpeg comment changer. Oh, and upon some looking around, there's one right on my system: wrjpgcom. So read the man page on it and see if that's what you want. -James Smaby ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user -- Rick Rosinski http://rickrosinski.com [EMAIL PROTECTED] ___ Gimp-user mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-user
