PNG image colours are off/wrong for XVideo output (XCB)

Bug #1437550 reported by Misaki on 2015-03-28
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This bug affects 1 person
Affects Status Importance Assigned to Milestone
vlc (Ubuntu)
Undecided
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Bug Description

I discovered this bug when testing a different package, eog: https://bugs.launchpad.net/ubuntu/+source/eog/+bug/1436595

When a PNG image is opened in VLC with Video output set to "XVideo output (XCB)", the colours are different than in other programs that display PNG files such as Firefox.

avplay, and presumably ffplay, display pngs the same way as vlc does using XVideo output (XCB). With a png that is a gradient from value 0 to 255 with one column of each value, vlc with Xvideo output (XCB) will have very slight apparent banding due to http://en.wikipedia.org/wiki/Lateral_inhibition or some other related effect. A histogram shows that about every 8th value is shifted up or down by 1. Colours are different by a greater degree and in a systematic way, so you don't need to have a uniform gradient or use a histogram to see the difference.

With a PNG, XVideo output (XCB) also had a green line on the right border.

With a video using the 'Sorensen video v.3' video codec, XVideo output (XCB) caused a green line to appear on the right side.

I have no idea if this is a bug in vlc or in a different project (XVideo, or XCB?) that vlc has no control over. It seems likely that bugs will tend to accumulate in places where it's hard to tell what project is doing things wrong.

With both still images (pngs and jpgs) and the Sorensen video v.3 codec, XVideo output (XCB) is the default output method if "Accelerated video output (overlay)", or "Overlay video output" in advanced options, is enabled. If it's disabled, then OpenGL GLX video output (XCB) is the default output method, which does not have any green lines, and renders images 'normally'. (That is, not the same as eog due to what seems like an eog bug as described in the linked bug report, but the same as several other programs.)

The various options have their own drawbacks, or it would be easy to just select a better method if one was bugged. In case it helps, I am attaching my notes on video settings.

I am using Ubuntu 14.10, and VLC version 2.2.0-pre2 Weatherwax, the witch.

Misaki (myjunkmail311006) wrote :
description: updated
description: updated
Changed in vlc (Ubuntu):
status: New → Confirmed
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