On Sat, 3 Nov 2007 00:06:18 +0100, Karl Günter Wünsch <[EMAIL PROTECTED]> wrote:
> On Friday 02 November 2007, Raphaël Quinet wrote:
> > There are also some improvements for the JPEG plug-in.  As I mentioned
> > some time ago, I would like to hide the current "quality" slider among
> > the advanced options, and replace it by a smaller selection of
> > pre-defined quality levels.  
> [...] every site I post my images to has 
> stringent restrictions on file size [...]
> Having preset quality settings really is no option, it is a major annoyance 
> in 
> Photoshop new users I spoke to always are struggling with!

It looks like what you want is a "Save for Web" feature (especially because
you mention posting images to some sites).  Photoshop offers two different
ways to save a JPEG image:

1) The normal Save assumes that you use JPEG like most other (lossless)
   image formats.  Professional users expect that the image will be saved
   with a rather high quality, will contain the appropriate color profiles
   and other metadata related to the image so that it can be integrated in
   a publishing process and eventually printed.  Photoshop allows the user
   to select quality levels between 0 and 12 (but each of them sets more
   than just the "quality" because the subsampling parameters are also
   affected).  The lowest level (0) is equivalent to quality 85 in GIMP,
   and the highest level (12) is somewhere between 97 and 98 in GIMP.  But
   using levels 11 and 12 is not recommended, so the recommended "High
   quality" level is 10, which is equivalent to quality 93 in GIMP.

2) The Save for Web feature assumes that you will put the image on some
   web site instead of printing it, so you care more about the size of
   the file than about its faithful rendering on a printer.  Save for Web
   allows you to remove most metadata from your image and gives you more
   control over some JPEG parameters that can help you to reduce the size
   of the file. Among others, it has a slider that goes from 1 to 100 so
   that you can fine-tune the size/quality and it also has an option that
   lets you enter the target file size so that Photoshop can select the
   compression level that brings you as close as possible to this target
   value.  Note that the 1-100 slider in Photoshop is not the same as in
   GIMP: the corresponding range in GIMP would be 55-98 (approximately).

Experienced Photoshop users will select "Save" or "Save for Web" depending
on what they intend to do with the image.  The goals are different and
almost mutually exclusive:
1) Save: high fidelity for printing, include all metadata, no need for a
   preview of the JPEG compression quality, no need to estimate the size
   of the file before saving
2) Save for web: focus on the size/quality trade-off, it is important to
   have a preview and to predict the size of the file, no need for
   metadata, assume sRGB color profile.

Currently, GIMP tries to do a bit of both in the same jpeg plug-in and
does not do either of them correctly:
- For a normal Save, it is a bit stupid to have a quality slider that goes
  from 0 to 100 if the useful range is only between 85 and 95.
- Showing only the quality slider in the default view misleads users into
  thinking that they only have to play with that value in order to reach a
  target size for the file.  Changing the subsampling parameters can be as
  important in order to reach the best size/quality ratio.
- It is necessary to check or uncheck several checkboxes in order to
  select if metatada and image thumbnails should be included or not.
- Several other checkboxes that are rarely used clutter the list of
  options.  The choice of DCT method and the inclusion of restart markers
  are special features that are almost never used (or used wrongly).

Considering all that, I think that it would be much better to provide a
simplified set of choices.  Each of them would combine several parameters
such as quality and subsampling.  This would streamline the interface for
the common case for our target users (cfr. GIMP vision).  Of course, the
advanced settings would still be available and this would include the old
quality slider if you think that it is useful.  But for the kind of use
case that you described, the ability to enter a target size for the file
would be more useful.  We could also change the jpeg plug-in so that it
remembers if the advanced options are expanded or not, and maybe make it
remember that across sessions.  So if you insist on using the old quality
slider for each image, you could still do that easily.


P.S.: For more information about the mapping between Photoshop and GIMP
      quality levels, see:
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