XnView Software

I just did a topic of missing info of lossy/lossless compression.

Anyway another thing that would be very useful to know from browser - info - properties is type of subsampling if the compression is lossy:

- 4:4:4 or 1x1 (no subsampling)
- 4:2:0 or 2x2, 1x1, 1x1 (most common I think)

- 4:2:2 or 4:2:2H ? (in horizontal direction there is subsampling but in vertical direction no chroma is lost)
- 4:2:2V? or 4:4:0? (in vertical direction there is subsampling but in hor direction no chroma is lost)


Most images seem to be missing this info. JPG does have it but in 2x2, 1x1, 1x1 format. AVIF, HEIC, JXL, WEBP seems to be missing it.

I would consider expressing subsampling in same format everywhere inside the program, maybe primarily as something like 444, 420, 422H, 422V but in settings user could choose if he wants also the other type of expression be visible or for both to be visible. Anyway it seems/feels to me that 444 and 420 are more common ways to express it.

JXL always is 444
WEBP lossy always is 420
AVIF and HEIC you have info in ExifTool tab

Kadet wrote: Wed Apr 30, 2025 9:38 pm JXL always is 444
WEBP lossy always is 420
AVIF and HEIC you have info in ExifTool tab

Are you sure that JXL (lossy) is always 444?
Raw 420 data consumes 60% of 444 data space. Seems akward if JXL didn't have opportunity to use this.

Exiftool tab is not a solution. It is good that it's there but when you browse through pics fast you prefer not to open it as it contains so much data. That is why it is best to have most important data in the first info page.

golemus wrote: Wed Apr 30, 2025 10:42 pm Are you sure that JXL (lossy) is always 444?
Raw 420 data consumes 60% of 444 data space. Seems akward if JXL didn't have opportunity to use this.

JPEG XL does use XYB color space by default. 420 subsampling is only defined for YUV color space.
Only legacy JPEG does use YUV color space by default.
For XYB color space only subsampling of the B (blue) component is defined.

JPEG XL does support YUV color space only for handling legacy JPEG files. For native JPEG XL files XYB 444 color space is the default. Subsampling of the blue component is the choice of the encoder. There is no command line switch to activate subsampling of the B component in the reference encoder for this, atm.
Subsampling the Y component reduces the resolution and the overall quality of an image, therefor this is a bad idea, the quality setting doesn't matter here.