[Digikam-devel] [digikam] [Bug 364790] Preview image shown too large

[DrSlony via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=364790

--- Comment #3 from DrSlony <bugs at londonlight.org> ---
"Yes, the 100% always refer to the original size of the image."
This is a bad design choice, and I will explain why.

When stretching the embedded JPEG preview to the reported raw size, digiKam's
preview is always blurry, soft and blocky when viewing raw files if one has a
camera which does not embed a full-sized JPEG preview in the raw file. In fact,
as most cameras which embed a "full-sized" JPEG preview don't actually make
that JPEG the same size as the reported original raw size, we are left with a
situation where digiKam's preview is never 1:1, never sharp, always stretched a
little or a lot...

Examples:
Nikon D700, reported original size 4288x2844, largest embedded JPEG size
4256x2832
Nikon D70s, reported original size 3040x2014, largest embedded JPEG size
3008x2000
Nikon D80, reported original size 3904x2616, largest embedded JPEG size
3872x2592
Pentax K10D, reported original size 3936x2624, largest embedded JPEG size
3872x2592
Pentax K-3, reported original size 6080x4032, largest embedded JPEG size
6016x4000
Canon 7D, reported original size 5360x3516, largest embedded JPEG size
5184x3456
etc.

If someone's camera makes the largest preview similar in size to the reported
original size, digiKam's preview is only a little stretched, only a little
blurry and blocky.
If someone's camera makes the largest preview half the size of the reported
original size, digiKam's preview is blurry and blocky beyond use.

If one's raw files contain a preview which is half the size of the reported
original raw size, if one sets digiKam as follows: "Preview Options > Embedded
view shows full image > Embedded preview", one expects 100% to show a sharp
embedded JPEG preview at 1:1 size, not this blurry mess
https://i.imgur.com/xfg9W09.png
At 100% I expect to see this https://i.imgur.com/1P8hEPN.jpg not this
https://i.imgur.com/cSHPxEL.jpg
>From the first I can tell the photo is perfectly in focus. From the second I
can tell nothing.

This stretching functionality is not helpful. How is one supposed to choose the
sharpest of three shots in digiKam? How is one suppose to choose the shot most
exposed to the right without clipping when digiKam insists on not allowing me
to see the neutral raw data in the preview? How am I supposed to compare
exposure-bracketed shots in digiKam if digiKam insists on applying auto-levels?

The preview digiKam shows is essentially broken with an inability to zoom to
1:1 pixel level, and it is impossible to set digiKam to show a full-sized
demosaiced no-auto-levels preview as I reported years ago. "Embedded view shows
full image" is not true, it is misleading. I wrote how to fix that here
https://bugs.kde.org/show_bug.cgi?id=319241#c9

I don't understand why someone would want a stretched, blurry, non-1:1 preview,
but if there is such a need, fine. Then I propose this solution:

Preview Options
The preview image for raw files shows:
● The largest embedded JPEG image.
○ Full-sized demosaiced raw data.
○ Half-sized demosaiced raw data.
Apply auto-levels to demosaiced raw data: (see bug #347010)
● No
○ Yes
Stretch the embedded JPEG preview to raw image size?
● No
○ Yes

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