CompuServe Messages

Hi Jim, Here is our basic problem again: "The basic problem seems to be that transparency factors are *added*, where they should probably be *averaged out*. Here is an example: a white, 80 % transparent segment is placed partially in front of a black background and partially in front of an opaque white object, which appeares dark grey, due to its shadows. The intersections of the two segments should now look grey also, even thou a little lighter. Fact is the intersection looks almost plain white. A probably better example: a dark red (140/0/0) segment that is 70 % transparent is placed in front of another dark red seg. (same color). This second seg now is opaque. The color of the intersection should also now be dark red, but it is bright red. The two reds seem to be added rather then averaged out: 140 red + 140 red = 280 red. This is turned to the closest number possible to display I presume: 255 (bright red). Instead the color-calculation should probably be something like this: 30 % of 140 (the transparent seg) + 70 % of 140 (the opaque seg) = 100% of 140 red. I am not sure about that thought Well I know that these examples are rather theoretical. The basic problem to me seems the color-theory here. You seemed to have used the additive color-mixing theory instead of the substractive-mixing. A good example for the unusabillity of additve color mixing might be my most gross red 70's ashtray. If I for instance put that monstruos deep red glass ashtray onto a green underground the green does not turn lighter in brightness – as in addtive color-mixing – it turns darker, turns more dirty, towards olive – just as in substractive color mixing. This is easily illustrated by black & white photography. Lets say you want to shoot a picture of a red brick-house that is partualy covered by ivy. If you use a red filter the bricks become very bright, they will apeare allmost white on the b/w print, wheras the ivy will turn allmost black. If you use a green gel on the lens, the ivy now will be allmost white and the brick-wall will appeare a lot darker then it actually is. In conclusion I think the only problem is the wrong colormode. Additive color-mixing does not work, because there is hardly a case where this is used in real life (hey, of course, on monitors). Most of the times you see substractive color-mixing. I can imagin that this problem sounds a lot more trivial then it is to program. But I still wanted to bring it to your attention just because we had some problems with a production recently. Another thing was the reflection on transparent segments. If you have a transparent white seg in front of a black background there is no reflection rendered, even if it is cranked all the way up." That was the first message. As you see, it is *not* a problem of removing parts of verlaping segs, its merely a problem of showing them but not in solid white. The actual problem occured on a scientiffic animation we did on eye-surgery (I know, some jobs you have to do). First a special type of syringe. That things had two tubes. Each of the tubes contains one component of a special fibrine glue. The animation had to look real, but schematic at the same time. Too much realism would have given it a too scary look. The way we have it now is far too schematic though, it doesn't look right. The clear cornea was an even bigger problem, since there was supposed to be an incision shown. That meant a *lot* of muscle motion and overlapping transparent pieces all over the place. We ended up doing most of the stuff in post. Thanks on the hint for the fog I'll give it a try, especially a rotoscoped black and white QT-Movie would probably work great for that. Any experience with that? Read ya, Peter.