[Bug 205776] New: "Embedded preview loads full image size" does not only do what it says, confusing users

https://bugs.kde.org/show_bug.cgi?id=205776





--- Comment #20 from Matti Rintala <bitti cs tut fi>  2009-09-01 20:24:04 ---
Marcel, radio button is great and makes the preferences visually clear! Just
what I was looking for but was too stupid to realise. :-)

With those user preferences, changes to the source should not be too difficult.
The old ...LoadFullImageSize... functions can remain there, they are controlled
by the radio buttons. New functions ...PreferEmbeddedPreview... should be
added.
With current source, loading full-size preview is easiest to implement by
setting preview size to a large value (65535 for example) in ImagePreviewView.
That should cause loading of embedded preview, but since the preview is smaller
than preview size, it is not scaled. Would that be ok?

If what I wrote above is ok, I'm willing to attempt writing a patch (no
promises though). But I'll wait for an OK from you before starting. (And if you
have different opinions about how this should be implemented, just say so.)

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--- Comment #21 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-09-02 21:06:58 ---
Some remarks:
You can start with a patch if you want. Setup, AlbumSettings field,
ImagePreviewView (and the very similar
utilities/lighttable/lighttablepreview.cpp, utilities/slideshow/slideshow.cpp)
I will tweak the loading code to make this work, I need to think about the
right solution there. You could add a third parameter to PreviewLoadThread's
loadHighQuality() to prefer embedded previews.

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--- Comment #22 from Matti Rintala <bitti cs tut fi>  2009-09-03 11:06:32 ---
Marcel,

I have no strong feelings about doing the patch. The feature itself (using
embedded raw previews in full size) is important for me, so I'm willing to try
to help, if help is needed. However, I have no prior experience in Digikam's
source, so I'm sure it takes me much more time to do the patch than if one of
you regular developers has time to invest in this matter. My goal is just to
get the needed feature as quickly as possible. :-)

I have some questions about the design:
- There are now two separate user preferences for preview quality, one for
previews and one for lighttable. Should the "use embedded preview for raw, if
available" setting duplicated to both places, so that the user can change
behaviour of album preview and lighttable independently?
- Earlier there has been only one bool option and one set of functions
(...LoadFullImageSize...) for preview quality. The most straightforward
solution for embedded previews would be to add another bool and set of
functions (...UseEmbeddedRawPreview...) to control this feature. However, I'm
no longer sure if that is good for future development. What if more control
over preview quality is needed later? Would it be wise to make a struct (or
enum) PreviewQuality, and replace current setLoadFullImageSize() functions with
setPreviewQuality() etc.? Then new preview quality options could be added more
easily without having to modify the intermediate classes which now only pass
through changes in preview quality. Currently PreviewQuality could contain just
two bools (full-size & embedded-preview), but later it could be expanded to
include user-defined maximum size etc, if need arises.

What do you think?

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--- Comment #23 from Mikolaj Machowski <mikmach wp pl>  2009-09-03 17:35:27 ---
After some contemplation pause I'd like to ask:

RAW users are more advanced users. If they want full version they want real
RAWs. If they want preview they probably want embedded full size preview. I any
case they don't want to use some crippled preview created from embedded
preview. Am I right or not? If I am right additional option isn't required,
just change mechanism, if I am mistaken... am returning under my bridge :)

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--- Comment #24 from Matti Rintala <bitti cs tut fi>  2009-09-04 09:55:44 ---
Mikolaj,

I think you have a good point. Shooting raw requires much more CPU power and
memory than jpeg. Which means that you probably do not have an old low-end
machine. Which makes the combination "use reduced-size embedded previews"
useless for raw shooters.

I see the following user groups:

1) Jpeg-only shooter
- Does not care how raw previews work
- May have a low-end machine, so reduced-size previews are useful

2) Raw-shooter whose camera stores full-size embedded previews
- Probably wants to use those full-size previews since they show how the
picture looked like on camera's lcd. Full-size is better for focus checking.
- Using embedded previews is also faster
- Wants jpegs full-size, since CPU and memory are not a problem

3) Raw-shooter whose camera only stores small embedded previews (are there such
cameras?)
- Small embedded preview shows how picture was on camera's lcd, but is not big
enough for checking focus etc.
- Needs full-size raw-decoded previews for checking focus
- Jpegs can be full-size
- I'll have to check which cameras belong to this group

For group 1 everything works now. For group 2 (me, and I think most
raw-shooters), the problem is that full-size preview does not use embedded
preview, even if it's available. For group 3 (if such group exists) things are
more complicated: for overall preview, small embedded preview is better. For
focus checking, full-size raw-decoded preview is better.

So what if: "Load full-size previews" uses embedded preview, if it's full-size.
Otherwise it uses raw-decoded preview. Would this be enough for every user
group?

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--- Comment #25 from Alex Tutubalin <lexa lexa ru>  2009-09-04 10:16:36 ---
Folks,

I think, that for most previews (_including_ focus-checking) one-half of camera
resolution is enough.

So, for 3-rd user group you may consider LibRaw/dcraw 'half mode'. This mode is
way faster than usual AHD interpolation and 1/2-resolution (1/4 in pixels) is
enough for most preview-related tasks.

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[Gilles Caulier-4]

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--- Comment #26 from Gilles Caulier <caulier gilles gmail com>  2009-09-04 10:26:26 ---
Raw full preview use already half mode currenttly. Only editor load full raw
image...

Gilles Caulier

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--- Comment #27 from Matti Rintala <bitti cs tut fi>  2009-09-04 11:29:27 ---
Gilles,

Does Digikam still use half-size previews? That's what I thought, but when I
tested with current trunk, 100 % full-size preview seems... well... full-size
for me.

Looking at the source, it seems that enabling full-size previews causes
previews to be loaded as normal images, not previews (but I'm not familiar
enough with the source to be 100 % sure).

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--- Comment #28 from Gilles Caulier <caulier gilles gmail com>  2009-09-04 11:37:10 ---
yes this is must be done :

- Raw  : preview full sized on ==> RAW half size image.
- JPEG : preview full sized on ==> real image size.

- Raw  : preview full sized off ==> RAW embedded JPEG.
- JPEG : preview full sized off ==> reduced version loaded using libjpeg.

Gilles Caulier

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--- Comment #29 from Matti Rintala <bitti cs tut fi>  2009-09-04 12:02:21 ---
Gilles,

I'm not sure I understand. That is how it is done now. That's exactly the
reason I filed this bug report.

That behaviour is ok for group 3 in my earlier comment. For group 2 (people
whose cameras store full-size embedded jpegs), current Digikam does not allow
showing the full-size high-quality jpeg at full size.

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--- Comment #30 from Matti Rintala <bitti cs tut fi>  2009-09-04 12:59:56 ---
I had time to do some quick tests:

The preview list mechanism in libexiv2 seems to work nicely. I wrote a small
program to list sizes of all embedded previews in raw files.

After trying that on raw files from several different cameras, I can say that
my "user group 3" exists, i.e. there are still lots of cameras whose raw file
does not contain a full-size embedded jpeg preview (or at least exiv2 could not
find it). The maximum size of embedded preview differs a lot, for example Sony
A380 seems to store an 1.5 mpix preview even though it's a 18 mpix camera. Old
cameras often stored only the 160x120 exif thumbnail.

So clearly it is not enough to use the embedded preview always when it's
available. In some cameras raw-decoding is the only way to get a full-size (or
even half-size) preview.

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--- Comment #31 from Mikolaj Machowski <mikmach wp pl>  2009-09-04 14:12:47 ---
@24, Matti

I am suggesting leaving interface as is and mechanics:

Use previews:
- reduced JPEGs in case of JPEGs; full-size JPEGs from RAWs whenever possible,
half-size previews for the rest

Full images:
- full JPEGs in case of JPEGs; in case of RAWs I have doubts, running full
blown RAW converter each time in Preview mode, or in LightTable seems...
problematic but as Matti wrote in #30 something more complicated have to be
done; I'd vote for simplified "import" of half-size image or even full-size but
not real RAWs processing.

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--- Comment #32 from Matti Rintala <bitti cs tut fi>  2009-09-04 14:39:16 ---
Mikolaj,

What about the following, which is evolved from you suggestion?

[ ] Embedded preview loads full-sized images (off)
- reduced JPEGs in case of JPEGs (limit to display size, as is done now)
- For raw, use smallest embedded preview that >= required size (display size).
If no embedded preview is available or largest embedded preview is less than
half of required size, use half-size raw-decoded preview (this makes sure
160x120 thumbnail previews etc. are not selected).
- Or this could be as you suggested, I was mainly thinking about libexiv2's
ability to list all available previews, so Digikam could pick one based on its
size

[X] Embedded preview loads full-sized images
- full JPEGs in case of JPEGs
- For raw, use largest preview available (including half-size raw-decoded
preview). This means that full-size embedded previews are chosen instead of
half-size raw-decoded preview, but that is better than small embedded previews.

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--- Comment #33 from Gilles Caulier <caulier gilles gmail com>  2009-09-04 14:44:43 ---
Sound fine for me.

Anyway, never load full RAW image in preview mode. It will take a while. Only
editor will use this way.

Gilles Caulier

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--- Comment #34 from Mikolaj Machowski <mikmach wp pl>  2009-09-04 15:20:05 ---
Sounds fine for me.

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--- Comment #35 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-09-04 16:44:47 ---
Ok I will change the logic accordingly in the previewthread and previewtask.

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--- Comment #36 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-09-04 19:31:38 ---
Support for Exiv2::PreviewManager need to be added to libkexiv2 directly.
For now I will try to work with the available libkdcraw methods.

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--- Comment #37 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-09-04 19:32:02 ---
SVN commit 1019872 by mwiesweg:

Implement suggested behavior from b.k.o. for loading fast + high quality
previews.

CCBUG: 205776

 M  +2 -8      previewloadthread.cpp  
 M  +2 -8      previewloadthread.h  
 M  +96 -33    previewtask.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=1019872

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--- Comment #38 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-09-04 19:35:53 ---
This is now an attempt to implement according to comment #32. As said above, we
want to use PreviewManager in the future but we can't at this point.
Please report if this is now as intended.
Color management for embedded previews (bug #195050) is not implemented yet.

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--- Comment #39 from Matti Rintala <bitti cs tut fi>  2009-09-07 12:20:22 ---
Marcel,

I had time to do some limited testing yesterday. To me this fix seems to work
as it should, but of course I could only test it with Nikon files and just a
couple of raw files from other sources. The behaviour seemed reasonable, but in
case of reduced-size previews I didn't try to estimate if the sizes of previews
were as suggested. :-)

Thanks for the fix!

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