On Mon, 13 Aug 2007 13:36:05 +0200, Raphaël Quinet <[EMAIL PROTECTED]> wrote:
> On Mon, 13 Aug 2007 07:10:30 -0400, Robert L Krawitz <[EMAIL PROTECTED]>
> wrote:
> > Would "Use existing image quality settings" be a better name for this?
>
> I considered naming this option "Use original quality settings", but
> one thing that I forgot to mention in my previous messages is that
> it is possible to write a script or plug-in that attaches different
> quantization tables to any image. [...]
Although I was a bit reluctant to do this, we could try to change the
name of this option to "Use original quality settings" or "Use quality
settings from original image" or something like that. This would
require several changes in behavior explained below. This new meaning
may not be appropriate if other quantization tables than the original
ones are attached to the image, but if we consider that usage to be an
exception, then maybe we can "optimize for the common case" if this
could make the option more understandable. Anyway, if we want to
change that string, then we have to reach a consensus on that in the
next few hours and make sure that it will not change again until GIMP
2.4 is out. We should be in string freeze now.
If we change the label, this also changes the meaning of the option
and this will require some changes to the code:
- Currently, "Use custom quality settings" is only available when the
quantization tables are non-standard ones. If the tables can be
generated by the IJG JPEG library, then the option is grayed out
because the user can get the same table with the existing "quality"
slider (and that slider is already set to the right value if the
quality of the original file is better than the user's default). If
that option is changed to mean "I want the same settings as the
original image" instead of "I want to use some non-standard tables",
then that option should always be available even if the original
image used standard quantization tables.
- Enabling that option should not only change the quality slider, but
it should also change the choice of subsampling parameters, even if
the chroma subsampling in the original image is not as good as the
user's defaults (i.e., if the default is 1x1 and the original image
used the lower quality 2x2 or 2x1). This would ensure that all
significant parameters from the original image are re-used when
saving. Note that it would be a one-way change: enabling the
option "Use original quality settings" would change the subsampling
parameters, but changing the subsampling parameters later would not
disable the option (unlike what is done when the quality slider is
moved).
- Optionally, the usage (or not) of optimized Huffman tables could be
detected in the original image and re-used when saving. I think
that it would be better to leave it always enabled (always optimize)
but if we want to be as close as possible to the original image,
then we could disable the optimization if the original image was not
optimized.
Implementing these changes would be easy (except for the last one,
maybe) and I know exactly what would have to be be changed so the code
itself is not an issue here. But we should quickly decide what this
option should mean. I like the current meaning ("custom tables") but
some of you think that it would be easier to understand something
referring to the original quality settings. If we can reach a quick
agreement on what is better (considering the differences explained
above) and if it is not too late for 2.4rc1, then maybe I could change
that option.
-Raphaël
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