[digikam] [Bug 322656] New: when opening a pic, dark areas show artefacts

[Axel Krebs]

https://bugs.kde.org/show_bug.cgi?id=322656

            Bug ID: 322656
           Summary: when opening a pic, dark areas show artefacts
    Classification: Unclassified
           Product: digikam
           Version: 3.2.0
          Platform: Ubuntu Packages
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Image Editor
          Assignee: [hidden email]
          Reporter: [hidden email]

opening a pic with image editor.

pic is jpg from NIKON D800

image editor show blackish areas as dark blue (=my setting)

these out-darkened areas show rectangular pattern in two cases:
1.) when applying correct color automatically _and_
2.) when opening this saved pic.



Reproducible: Always

Steps to Reproduce:
1. open image editor
2. open the jpg pics, created from NIKON D800
3. correct pics color setting automatically
4. use darklight with dark blue
5. watch the rectangular pattern.

potential risk: colored areas my show pattern in viewing/improving software

Actual Results:  
the rectangular pattern (will attach a screenshot)

Expected Results:  
for given homogeneous colored original areas, I will _never_ see any type of
pattern.

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[Axel Krebs]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #1 from Axel Krebs <[hidden email]> ---
Created attachment 81242
  --> https://bugs.kde.org/attachment.cgi?id=81242&action=edit
screenshot showing misleading pattern

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[Christoph Feck]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #2 from Christoph Feck <[hidden email]> ---
I do not see a misleading pattern, only camera noise.

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[Axel Krebs]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #3 from Axel Krebs <[hidden email]> ---
Created attachment 81244
  --> https://bugs.kde.org/attachment.cgi?id=81244&action=edit
suspected pattern with reddish underlied lines (vertical and horizontal)

the reddish marked lines- that's what I take for suspicious

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[Christoph Feck]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #4 from Christoph Feck <[hidden email]> ---
Check if they are 8 or 16 pixels apart. If they are, those are JPEG compression
artifacts.

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[Axel Krebs]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #5 from Axel Krebs <[hidden email]> ---
Christoph,

looks like beeing 8 pixels apart.

How does it refer on _png_-format I sent to KDE bug-report system??
Does png do similar artefacts as jpg?


Axel

Am 21.07.2013 20:28, schrieb Christoph Feck:
> https://bugs.kde.org/show_bug.cgi?id=322656
>
> --- Comment #4 from Christoph Feck <[hidden email]> ---
> Check if they are 8 or 16 pixels apart. If they are, those are JPEG compression
> artifacts.
>

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[Christoph Feck]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #6 from Christoph Feck <[hidden email]> ---
PNG is lossless, so the artifacts do not go away, if you convert from JPEG to
PNG.

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[Axel Krebs]

https://bugs.kde.org/show_bug.cgi?id=322656

--- Comment #7 from Axel Krebs <[hidden email]> ---
Am 22.07.2013 09:08, schrieb Christoph Feck:
> https://bugs.kde.org/show_bug.cgi?id=322656
>
> --- Comment #6 from Christoph Feck <[hidden email]> ---
> PNG is lossless, so the artifacts do not go away, if you convert from JPEG to
> PNG.
>
so: artefacts are no bug, but a feature of jpg?

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[Christoph Feck]

https://bugs.kde.org/show_bug.cgi?id=322656

Christoph Feck <[hidden email]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |[hidden email]
         Resolution|---                         |INVALID

--- Comment #8 from Christoph Feck <[hidden email]> ---
Yes, JPEG compresses 8x8 blocks independently. You can see it extremely when
using very low quality values.

Anyway, this is no bug. If you want no artifacts, your complete workflow must
avoid JPEG compression.

For more information, please ask in a forum.

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