hist_find_ndim crashes on images with an alpha channel

[travisbell]

Hi John, I've been working on migrating IM workflows over to vips and everything has been going very smoothly, thanks so much for your hard work and dedication.

One issue I have stumbled on is that when trying to use hist_find_ndim, vips is crashing on images with transparency. On Mac OS, I get:

$ vips hist_find_ndim tmp/test2.png tmp/test2_histogram.png
Abort trap: 6

And on Linux, I get:

vips hist_find_ndim tmp/test2.png tmp/test2_histogram.png
*** stack smashing detected ***: terminated
Aborted

This is on the latest build:

vips -v
vips-8.12.2-Tue Jan 25 09:34:32 UTC 2022

Is there something I need to do different with hist_find_ndim for these images? I couldn't find anyone else talking about this...

[jcupitt]

Hi @travisbell,

You're right, it doesn't check that bands <= 3, I'll change it.

As a workaround, you can take just the first three bands like this:

vips extract_band rgba.png rgb.png 0 --n 3
vips hist_find_ndim rgb.png histogram.png

Thanks for pointing out this dumbness.

[travisbell]

As a workaround, you can take just the first three bands like this:

vips extract_band rgba.png rgb.png 0 --n 3
vips hist_find_ndim rgb.png histogram.png

Perfect, this is working properly now.

Thanks for pointing out this dumbness.

I choose to believe just an oversight and not dumbness! 😉

[jcupitt]

OK, fixed for 8.12.3, I credited you, I hope that's OK.