'gdouble' is invalid or out of range for property 'xres'

When working with medical slides, the resolution is often specified in mm or even nm scale. resunit only accepts cm and inches, so by creating a WSI using tiffsave the values becmoe very small:

slide.tiffsave('slide.tiff', compression='jpeg', Q=80, tile=True, tile_width=128, tile_height=128, pyramid=True, depth=3,
               xres=0.00002333, yres=0.00002333, resunit='cm')

The values fall back to 28.3465 pixels/cm with a warning:

GLib-GObject-WARNING **: 17:22:50.793: value "0.000023" of type 'gdouble' is invalid or out of range for property 'xres' of type 'gdouble'

GLib-GObject-WARNING **: 17:22:50.793: value "0.000023" of type 'gdouble' is invalid or out of range for property 'yres' of type 'gdouble'

[jcupitt]

Huh you’re right, the tiff saver also clips the resolution:

        /* Don't write mad resolutions (eg. zero), it confuses some programs.
         */
        TIFFSetField( tif, TIFFTAG_RESOLUTIONUNIT, wtiff->resunit );
        TIFFSetField( tif, TIFFTAG_XRESOLUTION, VIPS_FCLIP( 0.01, wtiff->xres, 1000000 ) );
        TIFFSetField( tif, TIFFTAG_YRESOLUTION, VIPS_FCLIP( 0.01, wtiff->yres, 1000000 ) );

That’ll need changing too. It looks like there’s no easy workaround, unfortunately. We should make this change as a bugfix for 8.13.

The tiffsaver writes the same metadata for all pyramid levels, so you’ll see the same resolution. Imagine if you were printing the pyramid levels next to each other: would you want the levels to all be printed as the same size on the paper, or would you like the smaller levels to be smaller? It depends.

There’s no single correct answer, so libvips avoids automatic resolution changes.

[karray]

Yes, I think I solved my problem. Your comment from another discussion helped me