Re: [Gimp-user] lossless jpeg transformations

[pcg]

On Thu, Feb 17, 2005 at 06:02:31PM +0200, Alexander Rabtchevich <[EMAIL 
PROTECTED]> wrote:
> Could it be done via additional menu item: open for the lossless 
> transformations with only few operations active? The operation itself 
> has sense for digital images with portrait orientation. It would be nice 
> to store the original images without data loss but with corrected 
> orientation.

I think it makes very little sense to put this into the gimp. The extra work
is IMHO just not worth it, a specialized extra application would be more
useful.

Or a plug-in. The number of (useful, lossless) operations that can be done
on jpegs is very limited.

> By the way, I'm just curious, is it possible to apply different jpeg 
> settings to the different parts of an image?

Yes, you can vary quantizazion factors, but i don't think the jpeg library
can handle that. The best you can do with respect to such tricks is
to use scan scripts to achieve some effects, for example, the image
at URL has the monochrome
parts first which has the effect of first showing the grayscale image on
slow-enough connections.

> mean if the jpg image haven't undergo transformations affected the whole 
> image, the unaffected parts of the image could be saved as the original 
> compressed data without recompression (at least beyond adjacent points). 
> These pixels could be obtained by the simple comparison with the 
> original file.

That would be easy iff the underlying jpeg library supports it, and could
be limited to the jpeg plug-in. However, if you only use the ijg jpeg
library and take care of not changing the quantization factors you will
see that the pixels will already not change, i.e. there will be losless
compression.

So there is probably little demand for that. It would be far more useful
to have a way of knowing the quality the file was saved with (by the ijg
library) so it can be saved with the same quantizazion factor again, if
possible (i.e. as long as you use the same library to compres/decompress
the file).

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Re: [Gimp-user] lossless jpeg transformations

[Alexander Rabtchevich]

Could it be done via additional menu item: open for the lossless 
transformations with only few operations active? The operation itself 
has sense for digital images with portrait orientation. It would be nice 
to store the original images without data loss but with corrected 
orientation.

By the way, I'm just curious, is it possible to apply different jpeg 
settings to the different parts of an image? :) To different pixels? I 
mean if the jpg image haven't undergo transformations affected the whole 
image, the unaffected parts of the image could be saved as the original 
compressed data without recompression (at least beyond adjacent points). 
These pixels could be obtained by the simple comparison with the 
original file.

Joao S. O. Bueno Calligaris wrote:
Ok - I can think of one way of this being feasible - when the 
structure for the macro recorder is in place, or when an API for the 
undo steps is in place, the Jpeg filter could check, on save, if 
a) The image was loaded from a jpeg, and the original file is still 
available
b) The only operations performed on the image were images that can be 
performed in lossless way
And them it would:
c) Discard the Gimp image data, and perform the transform by itself on 
the orginal file.

--That means, that the jpeg plug-in would do the job, not the GIMP. It 
would be feasible, but I do not see it making much sense, and would 
be a terrible hack.
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--
With respect
Alexander Rabtchevich
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Re: [Gimp-user] lossless jpeg transformations

[Joao S. O. Bueno Calligaris]

On Thursday 17 February 2005 11:24, Alexander Rabtchevich wrote:
> There are some lossless jpeg transformations - flip and rotate (as
> Ifran view does under Windows). Are there any plans to introduce
> them in GIMP?
Hmmm.

No.
They would not make much sense in the GIMP.

Once an image is open, the GIMP doesn't 'know' were it came from - but 
for it's name and save options.
For this to work, the transform tools would have to be 'jpeg aware' - 
moreover, no other image editing of any kind could be done besides 
the rotate or flip, before the image is saved back again.

In short: you'd better doing these trasnforms with another program 
that doesn't do general editing of a image.

Ok - I can think of one way of this being feasible - when the 
structure for the macro recorder is in place, or when an API for the 
undo steps is in place, the Jpeg filter could check, on save, if 
a) The image was loaded from a jpeg, and the original file is still 
available
b) The only operations performed on the image were images that can be 
performed in lossless way
And them it would:
c) Discard the Gimp image data, and perform the transform by itself on 
the orginal file.

--That means, that the jpeg plug-in would do the job, not the GIMP. It 
would be feasible, but I do not see it making much sense, and would 
be a terrible hack.
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[Gimp-user] lossless jpeg transformations

[Alexander Rabtchevich]

There are some lossless jpeg transformations - flip and rotate (as Ifran 
view does under Windows). Are there any plans to introduce them in GIMP?

--
With respect
Alexander Rabtchevich
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