How to crop a jpg lossless?

[Andreas Borutta]

Hi,

in the preferences of DigiKam 0.9.3 I see, that the kipi module for
lossless editing is checked.

But I cannot find a command for lossless cropping of JPG.
I remember that a feature of lossless cropping are 8px steps. Lossless
cropping is not stepless.

Please could anyone give me a hint, how to crop lossless?

Another question:
When I draw a frame for (normal) cropping: How could I move the frame.
I do not want to change the size of the frame. It should just move.

Holding metakeys like shift, strg or alt or the right mouse key will
do not allow to move the frame.
Is there any way?

Thank you.

Andreas
--
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http://borumat.de/kubuntu/temp/bewaeltigt-unbewaeltigt

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[Gerhard Kulzer-3]

On Friday 09 May 2008 Andreas Borutta wrote:

> Hi,
>
> in the preferences of DigiKam 0.9.3 I see, that the kipi module for
> lossless editing is checked.
>
> But I cannot find a command for lossless cropping of JPG.
> I remember that a feature of lossless cropping are 8px steps. Lossless
> cropping is not stepless.
>
> Please could anyone give me a hint, how to crop lossless?
>
> Another question:
> When I draw a frame for (normal) cropping: How could I move the frame.
> I do not want to change the size of the frame. It should just move.
>
> Holding metakeys like shift, strg or alt or the right mouse key will
> do not allow to move the frame.
> Is there any way?
>
> Thank you.
>
> Andreas

Lossless cropping is not possible unless you crop to exactly 1/4 size or 1/16 and so on. This is a limitation of the underlying jpeg compression algo. Only lossless rotation is possible.

Best regards
Gerhard

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[Andreas Borutta]

Gerhard Kulzer schrieb:

> Lossless cropping is not possible unless you crop to exactly 1/4 size or 1/16 and so on. This is a limitation of the underlying jpeg compression algo.

Yes, I know.

> Only lossless rotation is possible.

Before I migrated to Linux I used the Windows application JPEGCrops
http://ekot.dk/programmer/JPEGCrops/
for lossless cropping.
It is based on jpegtran.

From the FAQ of JPEGCrops:
"What does lossless mean?
[...]JPEGCrops avoids this degradation by using JPEGTran which doesn't
repack the JPEGs: It merely throws away some of the data and keeps the
rest unchanged.

Can I crop as I like?
The lossless rotation only works when the width and the height of the
image can be divided by 16. Actually that's sometimes 8, but I haven't
found the time to make a check for that. The lossless cropping has
similar requirements for the upper left corner of the cropping area."

When the user draws a wire frame with the mouse, the frame will
increase or decrease automatically until the borders of the frame will
fit exactly for the nearest lossless frame size.

It worked perfectly.

What do you think about such a functionality for DigiKam?

For me, lossless cropping is an essentiell part of the workflow, not
just a nice to have feature.

The usability of JPEGCrops is (for me) the best I ever found for
cropping.
The user could interact with the mouse or with keyboard shortcuts
only.

I don't know any interaction design for cropping which allows faster
and easier cropping than JPEGCrops keyboard shortcuts.
May be you like to get a look. May be there are some details, which
fit for DigiKams transforming feature?

Just as a suggestion :)

I see, that you are one of the developers:

Thanks to you and to the other developers for DigiKam.
I like it a lot. :)

Andreas
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