Bad performance on PNG export
GIMP version: 2.10.4
Operating System: Linux (Kubuntu 16.04)
Package: flatpak
Description of the bug
Terrible performance when exporting PNG
Reproduction
- CPU is Intel i7-6820HQ.
- System monitor shows at least one core running 100% (3GHz) during the export.
- Plenty of free RAM.
- Exporting to SSD.
- Exporting same image to RGB 8-bit BMP is near instantaneous, so I/O problems unlikely
- PNG interlacing seems to have no influence, figures below are measured without interlacing
- Image is a 4096*4096 8-bit gamma, with a
Full saturation spectrum CCW
gradient drawn from NW to SE - Processing time seems related to the compression level
Measurements
* Compression 0: <1s
* Compression 1: <1s
* ...
* Compression 4: 0'02"60
* Compression 5: 0'03"94
* Compression 6: 0'07"60
* Compression 7: 0'12"26
* Compression 8: 0'55"43
* Compression 9: 2'18"49
- Using the opposite gradient (NE->SW) yields similar results
- Filling the image with random things (plasma) yields good results (5"70...)
- Filling the image with a grid yields good results too
Pathological case for the compression algorithm?