Decompose RGB to YCbCr Broadcast Standards in GIMP

This article provides a direct guide on decomposing an RGB image into YCbCr channels in GIMP according to specific broadcast television standards. By using GIMP's native color decomposition tools, you can isolate luminance (Y) and chrominance (Cb and Cr) channels calibrated to ITU specifications such as BT.601 for standard definition or BT.709 for high definition.

Step 1: Open Your Image in GIMP

Launch GIMP and open the RGB image you want to process via File > Open. Ensure the image is in RGB mode by verifying that Image > Mode > RGB is checked.

Step 2: Open the Decompose Tool

  1. Navigate to the top menu bar and select Colors.
  2. Hover over Components and click Decompose....

Step 3: Select the Broadcast Television Standard

In the Decompose dialog box, locate the Color model drop-down menu. GIMP provides multiple broadcast television presets:

  • YCbCr ITU R470: Corresponds to ITU-R BT.601 (formerly CCIR 601), the standard used for standard-definition television (SDTV) systems like NTSC and PAL.
  • YCbCr ITU R709: Corresponds to ITU-R BT.709, the standard used for high-definition television (HDTV).
  • YCbCr ITU R470 2PG: A variation based on specific PAL/SECAM gamma specifications.

Select the preset that matches the target broadcast delivery format of your project.

Step 4: Choose Output Configuration

In the same dialog box, choose how you want the channels arranged:

  • Check Decompose to layers to create a single new grayscale image where Y, Cb, and Cr exist as separate layers.
  • Uncheck the box to generate three separate grayscale image windows representing each channel independently.

Click OK to execute the decomposition.

Step 5: Understanding and Editing the Channels

The output will split the original image into three grayscale representations:

  • Y (Luma): Contains the brightness and detail information of the scene.
  • Cb (Chroma Blue): Represents the blue-difference component (\(B - Y\)).
  • Cr (Chroma Red): Represents the red-difference component (\(R - Y\)).

Step 6: Recomposing the Image (Optional)

If you edit individual Y, Cb, or Cr channels, you can merge them back into an RGB image:

  1. If decomposed as layers, go to Colors > Components > Recompose to update the original image directly.
  2. If working from separate channels or if the link is broken, select Colors > Components > Compose..., set the color model back to the matching ITU standard, assign the appropriate channel to each slot, and click OK.