Grayscale TIFF colorization exports as low-resolution unless transparency is forced (InDesign 21.3 / macOS 26.4)

Environment:

• InDesign version: 21.3
• macOS version: 26.4 (build 25E246)
• Hardware: Mac (Apple Silicon, exact model available on request)
• PDF export presets tested: High Quality Print, custom (no compression), PDF 1.3–1.8
• GPU on/off tested

Description of the issue:

Grayscale TIFF images placed in InDesign and colorized using the InDesign color tools export as visibly pixelated (low-resolution) in PDF.

• The source images are high-resolution and correctly linked
• The display in InDesign (high quality preview) is perfectly sharp
• The issue appears only after PDF export
• RGB/JPEG images do not show this problem

Key observation:

The issue disappears when transparency is introduced in the layout.

In my case, applying a white rectangle over the page with blending mode set to “Multiply” forces correct rendering of all affected images.

This suggests that:

• When no transparency is present → InDesign uses a rendering path that rasterizes colorized grayscale images at low resolution
• When transparency is present → a different rendering pipeline is used, producing correct high-resolution output

Conclusion:

This behavior strongly indicates a bug in the non-transparency rendering pipeline, specifically affecting:

• grayscale TIFF images
• colorized in InDesign

Additional issue (performance / thermal behavior):

Since recent versions of InDesign (including 21.3), the application systematically triggers high CPU usage, causing:

• constant activation of cooling fans
• noticeable system heat, even on relatively simple documents

This behavior appears abnormal compared to previous versions and may indicate a performance regression.

Expected behavior:

• Consistent high-resolution output regardless of transparency presence
• No need for artificial transparency to obtain correct rendering
• Stable CPU usage during standard layout and export operations

Workaround:

• Forcing transparency globally (e.g. overlay with Multiply blending mode) resolves the issue
• However, this is not a viable long-term production workflow, especially for complex layered documents

Request:

Please investigate:

1. The rendering difference between transparency and non-transparency pipelines
2. The rasterization behavior of colorized grayscale images
3. The recent increase in CPU usage and thermal load

I can provide sample files if needed.