Interactive adjustment of image quality for lossy image formats ...

Hi guys,

Me again.

As previously discussed, in order for the new jpeg-2000 plugin to be
useful, it is
necessary to be able to save images with user selectable compression ratios.

I've taken a look at the jpg save setup in GIMP and have noted that there
is a quality
slider, but, unless I'm missing something (which is possible - I only had a
quick look),
it is not possible to interactively inspect the compressed image as the
slider is moved.

This is inefficient because artists won't know what the compressed image is
going to look
like until they open it up again. It would be far better to be able to
adjust the image
quality in real time.

So, my question - does GIMP provide the ability to do the above in some way
or do I need
to write code to open a temporary inspection window within the save
callback ?

Follow on - this is some way off at the moment ... Jpeg-2000 supports
rectangular regions
of interest (ROI) to enable some parts of an image to be compressed at
different levels
from others, so for example, a sign with text could be compressed at high
quality so you
can read it, whilst the background could be more fuzzy, as it's not so
important to be
able to make out the detail so accurately. Is there some way we can mark
rectangular
areas that don't get saved in the image, but that are available in the save
routine for
ROI optimisation ? Layers ?

Thanks in advance for any assistance you are able to offer.

Best regards,
Steve.

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steve@advance-software.com wrote:
> Hi guys,
>
> Me again.
>
> As previously discussed, in order for the new jpeg-2000 plugin to be
> useful, it is
> necessary to be able to save images with user selectable compression ratios.
>
> I've taken a look at the jpg save setup in GIMP and have noted that there
> is a quality
> slider, but, unless I'm missing something (which is possible - I only had a
> quick look),
> it is not possible to interactively inspect the compressed image as the
> slider is moved.

Hi Steve

Check the 'Show preview in image window' checkbox. The way it is
implemented is rather hackish IIRC but there's a preview at least.

- Martin

Hi Martin,

Thanks for your prompt response.

Hackish is fine ...

Next job, locating the source to the jpeg plugin so I can grab the basics
and merge ...

Best regards,
Steve.




Original Message:
-----------------
From: Martin Nordholts enselic@gmail.com
Date: Sat, 15 Nov 2008 15:24:33 +0100
To: steve.williams@advance-software.com,
gimp-developer@lists.xcf.berkeley.edu
Subject: Re: [Gimp-developer] Interactive adjustment of image quality
forlossy image
formats ...


steve@advance-software.com wrote:
> Hi guys,
>
> Me again.
>
> As previously discussed, in order for the new jpeg-2000 plugin to be
> useful, it is
> necessary to be able to save images with user selectable compression
ratios.
>
> I've taken a look at the jpg save setup in GIMP and have noted that there
> is a quality
> slider, but, unless I'm missing something (which is possible - I only had
a
> quick look),
> it is not possible to interactively inspect the compressed image as the
> slider is moved.

Hi Steve

Check the 'Show preview in image window' checkbox. The way it is
implemented is rather hackish IIRC but there's a preview at least.

- Martin

steve@advance-software.com wrote:
> Hi Martin,
>
> Thanks for your prompt response.
>
> Hackish is fine ...
>
> Next job, locating the source to the jpeg plugin so I can grab the basics
> and merge ...
>

The code for it is in plug-ins/file-jpeg/jpeg-save.c

- Martin

On Sat, 2008-11-15 at 15:24 +0100, Martin Nordholts wrote:
[...]
> Check the 'Show preview in image window' checkbox. The way it is
> implemented is rather hackish IIRC but there's a preview at least.

It temporarily adds a layer to the image, to do the preview.

You also need to have enabled preview to find out what the
file size will be -- a hassle when trying to get an image
as close as possible to just under 25 MBytes for uploading to
a stock place or for making a print somewhere with a limit...
you don't necessarily want to see the preview at that point.

But it's still useful, even if a little hackish with the layers :)

Liam