What's the mean of levels and opacities?

[Thatfreesky]

I can not understand the effect of slides of levels and opacities? I think that the API is not clear about this part of content. Can anyone help me?

[maartenbreddels]

Hi,

I wanted to explain this by updating the docs on this, but let's start here first. A transfer function maps voxel values in the range [0, 1] to rgba (rgb+alpha) colors. In ipvolume, a volumetric cube is first normalized to the [0, 1] range, unless datamin, datamax is provided, where clipping is applied when the values are outside this range. The default transfer function exists of 3 gaussian bumps, where the location of the bumps are provided in level, the sigmas/widths by level_width, and the height/opacity by opacity. The first bump causes will result in red values, the 2nd in green, and the 3rd in blue. Note that this is the default transfer function, it should be possible (but haven't tested that for a while) to define your own transfer function.

Would really like to have an example reproducing for instance this

Does this help? I will keep this open until transfer functions are better documented.

[Thatfreesky]

Thanks for your help. I think I need to learn some details about the transfer functions.

[satra]

it looks like the upperbound for opacity is hardcoded here. is there a way to modify this programmatically at present?

https://github.com/maartenbreddels/ipyvolume/blob/master/ipyvolume/transferfunction.py#L88

[maartenbreddels]

Hi Satrajit,

yes, I have to say that the transfer functions are something that needs more work, but I've added a max_opacity keyword to volshow(..) as you can see in the referenced commit. It would be possible btw to get a reference to this max opacity, but it's difficult to obtain, and this change makes more sense I think.

cheers,

Maarten

[maartenbreddels]

PS: Please raise a new issue next time :)

[satra]

thanks. will do