On 05/27/2012 08:26 PM, gfxuser wrote:

Hi,

reading some of the JPEG related articles here I wondered whether GIMP or GEGL can do lossless rotation and cropping on JPEG images. Can you tell me more about it?

Thanks, grafxuser

For rotation, that would only work on images with dimensions that are a multiple of 8. For cropping, that only works if you crop on 8-pixel boundaries from the origin corner.

Otherwise, this also assumes that JPEG is an "editable format", while the recent kerfuffle around the Export function has demonstrated that it is not, in the current vision.

For a non GIMP solution (with severe constraints on the rotation and cropping parameters, as is pretty much unavoidable): http://jpegclub.org/

I've read that Picasa (Google's program) might be able to perform lossless rotations, but I'm just going by what I've read. (Source
)

Apparently there are ways to test if the tool you use makes use of lossless rotation. This page lists some:
http://www.impulseadventure.com/photo/lossless-rotation-test.html

This page also has a nice explanation of lossless rotation and its finer nuances:
http://www.betterjpeg.com/lossless-rotation.htm

From what I've learned so far, I think in the end you just have to relax about all this stuff and not worry about it too much, though it does help to know what's happening when you do certain things (such as rotate a jpeg).

On Mon, May 28, 2012 at 5:31 AM, gfxuser wrote:

Ofnuts wrote:

On 05/27/2012 08:26 PM, gfxuser wrote:

Hi,

reading some of the JPEG related articles here I wondered whether GIMP or GEGL can do lossless rotation and cropping on JPEG images. Can you tell me more about it?

Thanks,
grafxuser

For rotation, that would only work on images with dimensions that are a multiple of 8. For cropping, that only works if you crop on 8-pixel boundaries from the origin corner.

Otherwise, this also assumes that JPEG is an "editable format", while the recent kerfuffle around the Export function has demonstrated that it is not, in the current vision.

Thanks, Ofnuts.

Yes, 'Export vs. Save' was a long discussion and I don't want to boost it again. Although it takes a little getting used to I can live with the new behaviour. Despite of that I sometimes wondered in the past whether GIMP will introduce new compression artifacts if I rotated or cropped an existing JPEG image (yes, there are some cameras where saving in JPEG of sufficient quality is the best choice. Shall we not use them anymore?).

Best regards,

grafxuser

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On 05/30/2012 05:55 PM, Bruce wrote:

I've read that Picasa (Google's program) might be able to perform lossless rotations, but I'm just going by what I've read. (Source )

Apparently there are ways to test if the tool you use makes use of lossless rotation. This page lists some: http://www.impulseadventure.com/photo/lossless-rotation-test.html

This page also has a nice explanation of lossless rotation and its finer nuances:
http://www.betterjpeg.com/lossless-rotation.htm

From what I've learned so far, I think in the end you just have to relax about all this stuff and not worry about it too much, though it does help to know what's happening when you do certain things (such as rotate a jpeg).

The best (and fastest....) way to rotate a JPEG is to change its orientation flag...

On Thu, 2012-05-31 at 01:04 +0200, Ofnuts wrote:

The best (and fastest....) way to rotate a JPEG is to change its orientation flag...

Not all programs honour the orientation flag.

Windows Explorer's thumbnails used to be an example, don't know if that's still true in Windows 7.

Liam