#Problem with decal/alpha
15 messages in this thread
I'm having problems using video rotoscoped with the PAR (thanks Greg, is
working wonderful) as a decal. I wish to use all the frame as opaque using an
all white alpha channel, but I have no success with this. The Material Editor
does not recognize an all white alpha channel.
I tried this as a check:
1.- I rendered an object that does not fill the viewport with alpha on and
alpha split set to no. I can view in the material editor the alpha channel.
2.- I scaled the same object to fill all the viewport, rendered again, and now
the material editor says the image does not have alpha channel, but the file
sizes and Photoshop confirmed that the extra channel is present.
3.- As a test, with Photoshop I blackened a single pixel in the alpha channel
of test 2, and now the Material Editor shows it and admits its existence.
Any help is very appreciated, Vanny
Try turning on Ignore Map Alpha in the mapping parameters dialog. We
_deliberately_ look for a special case of all 255-luma pixels in the alpha
channel, and assume that it came in from a source that didn't "know how" to
write an alpha channel. Either way, since it's totally opaque, you shouldn't
have a problem decaling it.
– G
Thanks Gary, but…
Ignore Map Alpha works well. But I'm at the mercy of the top-left pixel and in
some frames makes the decal transparent in some areas, which I don't want. With
rotoscoped frames, any color could be the key.
I cannot surround the frame with a key color for the same reason, and also is
too much work. So I need the alpha channel.
But a complete opaque channel (white) is not recognized by the Material Editor.
I just tested with Photoshop. I made one alpha all white, the Material Editor
reverted to a RBG setting (because it cannot see the alpha channel), and
transparency appeared. Then I just cleared one pixel with Photoshop, and all
worked ok, except in the cleared pixel.
I can tweak the alpha channel, but for 400 frames…
Maybe a button in the decal dialog that makes it all opaque can work.
Thanks, Vanny
Ah ha… since you've got similar-colored pixels in the rest of the image,
you're getting some see-through areas. hmmm… You seem to have brought up a
limitation of the permutations in the Mapping Parameters dialog. Good one.
You're right in that there's a simple workaround… putting a black dot in one
of the corners of the alpha channel (actually, it doesn't have to be black…
something near 254 ought to do it). However, for 400 frames…
You could automate this by using an IXP that just altered one pixel in the
alpha channel automatically, and then wrote out the altered frame. We could
pull an IXP like that together pretty quickly if we had time, but most of this
week is out (until next weekend). If you need it badly and still haven't done
it manually by Friday let me know and I'll see if we can squeeze in some time
on Saturday to do it.
– G
>> …putting a black dot in one of the corners of the alpha channel…
I missed the start of this. Regardless, it sounds like something that wouldn't
take more than a couple of minutes. If you define it a little more I might be
able to get it together for tomorrow.
Basically, what he needs is an IXP that reads in a 32-bit .tga file and
modifies the upper-left pixel (0,0) of the alpha channel to be a value (let's
say) of 250. It could then just write the modified data to the prexisting file
(to save space).
You're a prince, Gus!
– G
Thanks Gary:
I'm not in a hurry. I'll look for another workarounds. I think the best way to
go in this case is a routine that takes separate targa and alpha files and
makes a single 32 bit targa.
I'll have to check if some image processing program does that.
Thanks again, Vanny
It looks like Gus is offering to help you out. Why don't you get together with
him on email and let him know exactly what you need.
– G
Just now! Thanks, Vanny
Just now! Thanks, Vanny
I uploaded a file called ADOT.ZIP. That's the IXP you were looking for. It will
set the upper left pixel (of the alpha channel) to whatever value you tell it
to.
Vanny:
Gary has the answer for you, I just wanted to jump in and say hi, and that I'm
glad everything is working well for you!
Greg Pyros
Hi Greg:
I just came from Miami, installed everything and worked out the rat nest in the
back of the computer. All is working well, and convinced me to buy the Pentium
for more slots and bays.
Vanny.
vanny:
i might be completely out to lunch on this one, but could'nt you achive the ixp
effect through video post?
you can prepare a special map with the black dot on the corrner and leave te
rest completly transparant through the rgb setting. then compose the rotoscoped
images and the black dot map through video post.
thsi will automatically change all your images. tell me what you think about
this and if i am completely off please explain.
thanks
ara
Ara:
The problem is that I cannot make a full screen opaque decal using alpha
channel. The black dot (better an almost white dot) is in the alpha channel so
the Material Editor can recognize it. Currently, the Material Editor treats an
alpha channel made of all pixels at level 255 as no alpha channel.
All I need is merge a sequence of separate RGB file with an alpha channel file
to go.
Vanny