Bug 322656

Summary:	when opening a pic, dark areas show artefacts
Product:	[Applications] digikam	Reporter:	Axel Krebs <axel.krebs>
Component:	ImageEditor-Canvas	Assignee:	Digikam Developers <digikam-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	caulier.gilles, cfeck
Priority:	NOR
Version:	3.2.0
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
Latest Commit:		Version Fixed In:	7.6.0
Attachments:	screenshot showing misleading pattern suspected pattern with reddish underlied lines (vertical and horizontal)

Description Axel Krebs 2013-07-21 15:05:46 UTC

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.

Comment 1 Axel Krebs 2013-07-21 15:07:40 UTC

Created attachment 81242 [details]
screenshot showing misleading pattern

Comment 2 Christoph Feck 2013-07-21 16:07:07 UTC

I do not see a misleading pattern, only camera noise.

Comment 3 Axel Krebs 2013-07-21 16:20:19 UTC

Created attachment 81244 [details]
suspected pattern with reddish underlied lines (vertical and horizontal)

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

Comment 4 Christoph Feck 2013-07-21 18:28:12 UTC

Check if they are 8 or 16 pixels apart. If they are, those are JPEG compression artifacts.

Comment 5 Axel Krebs 2013-07-21 19:37:21 UTC

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 <christoph@maxiom.de> ---
> Check if they are 8 or 16 pixels apart. If they are, those are JPEG compression
> artifacts.
>

Comment 6 Christoph Feck 2013-07-22 07:08:25 UTC

PNG is lossless, so the artifacts do not go away, if you convert from JPEG to PNG.

Comment 7 Axel Krebs 2013-07-22 07:35:28 UTC

Am 22.07.2013 09:08, schrieb Christoph Feck:
> https://bugs.kde.org/show_bug.cgi?id=322656
> 
> --- Comment #6 from Christoph Feck <christoph@maxiom.de> ---
> 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?

Comment 8 Christoph Feck 2013-07-22 11:37:44 UTC

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.