View Full Version : HV Imag Clip Sprites... they make no sense at all?

12-06-2004, 08:02 PM
OK, be warned... frustrated user about to rant... I'll try to stay calm...

I use Lightwave for a lot of astronomical visualizations (NASA press releases, in fact), and thus I often need to do "fuzzy" things like nebulae. I've been working with Hypervoxels since the week they were released and they STILL never make any sense. I like software that behaves in an expected manner, which you can approach with an idea in mind, and make it work. This is virtually impossible in Hypervoxels, doubly so due to the amazingly scant documentation they've received since their inception.

Here's my problem of the day. I want to use HV image clip sprites so I can render a number of illustrations I've created in a 3D environment. I do NOT necessarily want them all to be additive (in HV terms, I need opacity > 0)

So I run a test. I make an orange image in Photoshop. I add to it an alpha channel of a squiggle (soft-edged). I render it in HV, with all basic settings (luminosity, opacity, density) all set to 100% I add the clip, choosing "embedded" as the alpha.

When I render it, all the squiggles have DARK borders. I didn't put them there. The image is flat orange. I can't make them go away. I don't want them. But HV has decided that they need to be there. (image attached)

What use is a sprite with alpha mode if HV adds dark borders to everything?

In fact, I'm a little confused why most of the settings exist at all. For instance, let's look at the alpha setting. What if I try the same thing by just painting an orange squiggle on a black background, then choose the Alpha Black mode? Well, I get ugly aliased squiggles with really dark edges because it only clips out 100% black, and doesn't figure on pre-multiplied. Who would ever make use of aliased clippings like that for sprites? Does it serve any purpose?

As far as I can tell, the only mode for sprites that works reliably is to use opacity of 0 so they're purely additive. That's the only way you can get rid of the black edges. So much for using other values of opacity.

If anyone has had better luck using opaque or semi-opaque image sprites, I'd love to hear about it...

PS - On another aside, some time ago I found that if you use image clip sprites and allow any kind of stretch (like along direction of motion), all HV does is to apply an elliptical crop to your image (as opposed to its usual circular crop) instead of taking the circularly-cropped image and elongating it. <sigh>

12-08-2004, 08:15 AM
agree with you: the alpha channel seems to be broken in some way.
But in your case, using the luminosity channel or deactivate the solid button could be a method working around the problem.

12-09-2004, 12:26 AM
Alas, no, I've tried both of those options and you just can't get rid of the black edging.


I'm glad to hear that someone else at least has noticed this...

12-12-2004, 01:48 PM
sorry that it does not function...

I've played around with the settings, and it seems that not alpha itself is the troublemaker but a bug in the opacity.
But this "insight" will not help you at all:
Using a local density gradient, I get some really strange results, but nothing really useable.

If you need this on a black / dark background you can keep opacity at 0 and play only with luminosity and density values. (So you'll get an additive behavior).
For opaque objects or on white background I really cannot help you.

12-13-2004, 12:23 PM
Haven't run into this SPECIFIC problem, but usually when I get unexpected borders on fuzzy objects, it's the background bleeding through the soft edge. Are you rendering against a black background by any chance?

12-13-2004, 10:16 PM
Nope, it's a white background, as you can see in the attached image. But even if it were a black background that wouldn't explain why the overlapping sprites had dark edges since what's bleeding through would be the color of the sprite behind.

I'm pretty sure this is a real bug, or at the least an undesirable behavior that greatly restricts your choices if you want to use opaque sprites.

It's almost like it's taking the straight alpha, using it to make a "premultiplied with black" image, then reapplying the alpha.

12-14-2004, 02:27 PM
I'm pretty sure this is a real bug,
after a few experiments later: me too

A good way to see that something is going definitive wrong is, to take a look into the alpha channel of the rendered image.

... but still I got one possebillity I've to check out.