bytedeco/javacv

Slight but noticeable color shift when using FFmpegFrameGrabber

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#2,172 opened on Jan 18, 2024

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Description

There's a slight change in colors when grabbing frames with FFmpegFrameGrabber and the bgr24 pixel format, compared to what the ffmpeg command line tool produces when saving frames as PNGs or when compared to ffplay's output. Parts of the image are sometimes more contrasty, which makes compression artifacts more pronounced (e.g., banding with some low-contrast gradients).

I'm attaching the same frame fragment, one grabbed with FFmpegFrameGrabber and the other saved as a PNG with the command line tool.

Correct colors (straight from ffmpeg): ffmpeg

Colors from the same frame grabbed with FFmpegFrameGrabber: grabbed

The FFmpegFrameGrabber one has a slight, greenish tint (judging purely by eye).

To get the PNGs with the command line tool, I used this:

ffmpeg -i in.mp4 -t 00:00:01 out/%04d.png

Contributor guide

Research direction
Examine the pixel format conversion in FFmpegFrameGrabber, specifically the bgr24 to RGB conversion, and check if color matrix or sws flags are applied correctly.
Tech stack
java
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaFFmpeg
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60