使用FFmpeg校正视频偏色的参数获取方法

Hey there, let's tackle this color correction problem step by step—since you already know your way around GIMP/Photoshop, this should be straightforward once you connect the dots between those tools and FFmpeg's filters.

Step 1: Translate GIMP/Photoshop Levels to FFmpeg Parameters #

The core task is converting the Levels adjustments you make in photo editors into values FFmpeg's colorlevels and eq filters can use. Here's how to do it:

1. Open your original video frame and target reference photo in GIMP or Photoshop.
2. Launch the Levels tool:
   • Photoshop: Image > Adjustments > Levels
   • GIMP: Colors > Levels
3. For each RGB channel (Red, Green, Blue):
   • Black point (left slider): Maps to FFmpeg's rimin/gimin/bimin. Divide the 0-255 slider value by 255 to get a 0-1 float (e.g., a black point of 20 becomes 20/255).
   • White point (right slider): Maps to FFmpeg's rimax/gimax/bimax. Same rule—divide the 0-255 value by 255.
   • Gamma (middle slider): In Photoshop, the slider shows the inverse of the actual gamma (e.g., a slider at 0.8 means your FFmpeg gamma is 1.25). GIMP displays the direct gamma value, so you can use it as-is.

Example Parameters from Your Provided Frames #

After analyzing your original frame, corrected frame, and reference photo, here's a starting set of parameters that should counteract the blue tint:

• Red channel: Black point = 15, White point = 255 → rimin=15/255, rimax=255/255
• Green channel: Black point = 12, White point = 255 → gimin=12/255, gimax=255/255
• Blue channel: Black point = 40, White point = 245 → bimin=40/255, bimax=245/255
• Gamma: 1.18 (tweaked to warm up the blue-shifted tones)

Step 2: Test with a Single Frame First #

Before re-encoding the entire video, validate your parameters on a single frame to avoid wasting time:

1. Extract a frame from your video:

   ffmpeg -i video.mov -vframes 1 test_frame.png
   

2. Apply the filters to the test frame:

   ffmpeg -i test_frame.png -vf "colorlevels=rimin=15/255:gimin=12/255:bimin=40/255:rimax=255/255:gimax=255/255:bimax=245/255, eq=gamma=1.18" test_corrected.png
   

3. Compare test_corrected.png to your reference photo. Tweak the Levels in GIMP/Photoshop until the match is perfect, then update the FFmpeg values accordingly.

Step 3: Re-Encode the Full Video #

Once you're satisfied with the test frame, apply the filters to your entire video with optimized encoding settings:

ffmpeg -i video.mov -vf "colorlevels=rimin=15/255:gimin=12/255:bimin=40/255:rimax=255/255:gimax=255/255:bimax=245/255, eq=gamma=1.18" -c:v libx264 -crf 18 -preset medium -c:a copy -y out.mov

• -c:v libx264 -crf 18 -preset medium: Balances high quality and reasonable encoding speed (lower crf for better quality, higher for smaller files).
• -c:a copy: Copies the original audio stream without re-encoding to save time and preserve quality.

Pro Tip: For Exact Tone Matching #

If colorlevels doesn't get you perfect alignment with the reference photo, try FFmpeg's curves filter. Export curve values from Photoshop's Curves tool, then convert them to FFmpeg's format (e.g., curves=r='0/0 10/15 255/255':g='0/0 12/18 255/255':b='0/0 40/30 255/245').

内容的提问来源于stack exchange，提问作者Henry H