minor change when lossless saved?

thire · Post by **thire** » Mon Aug 15, 2005 11:30 am

I opened an original (from my EOS 350D) jpg file and performed the following excellent test for lossless rotation:
http://www.impulseadventure.com/photo/l ... -test.html
And (in GIMP) it showed some minor differences, here is a screenshot of the historgramm:
http://fsmat.htu.tuwien.ac.at/~thire/we ... ssless.png
And (I don't know much about all this, perhaps this is normal), the filesize increased from 1.1MB to 1.6MB.
Why / help / ideas / bug ?
Thomas

marsh · Post by **marsh** » Mon Aug 15, 2005 2:59 pm

There are 2 rotate functions:
Image>'Rotate' requires saving jpg file according to quality settings for changes to be permanent. It is lossless only with lossless formats, like BMP.
Tools>JPG Lossless Tranformations>'Rotate' modifies original file directly- saving jpg again is not necessary.

thire · Post by **thire** » Mon Aug 15, 2005 3:05 pm

I clicked on "lossless operation"-> rotate 90°
and then I saved it in jpg at 100% quality.
th

marsh · Post by **marsh** » Mon Aug 15, 2005 3:38 pm

thire wrote:I clicked on "lossless operation"-> rotate 90°
and then I saved it in jpg at 100% quality.
th

Then if the original's quality settings were less than 100%, saving it again could make file size much larger. With 'lossless transformation', you should have seen no file size change because saving it again was not needed.

ckv · Post by **ckv** » Fri Aug 19, 2005 7:56 pm

Yeah no need to save. And also notice the 'Trim image...' option in lossless Transfomations dialog.

By the way. Is there any way to delete EXIF data with lossless saving the file in XnView?

Guest · Post by **Guest** » Sat Aug 20, 2005 7:37 am

well, I saved with 100% quality and there is a very minor difference between the images. Perhaps someone can try the procedure (link above) as welland tell us about his/her results?

th

ckv · Post by **ckv** » Sat Aug 20, 2005 9:06 am

Anonymous wrote:well, I saved with 100% quality and there is a very minor difference between the images. Perhaps someone can try the procedure (link above) as welland tell us about his/her results?
th

Of course jpg isn't lossless format. As said before no need to save when using 'JPG lossless Transfomations'.

thire · Post by **thire** » Thu Aug 25, 2005 2:20 pm

ckv wrote:Yeah no need to save. And also notice the 'Trim image...' option in lossless Transfomations dialog.

By the way. Is there any way to delete EXIF data with lossless saving the file in XnView?

Okay, now I understand. (took me some time, ha?)
thanks for the answer. I checked it and XnView does a perfect lossless job!

th

ckv · Post by **ckv** » Thu Aug 25, 2005 2:30 pm

thire wrote:I checked it and XnView does a perfect lossless job!
th

Good to hear. Thanks for checking that again.

thire · Post by **thire** » Thu Aug 25, 2005 2:32 pm

yep, a fast GIMP analysis confirmed that nothing is lost: really lossless

perfect!

th