#Video Post Prob URGENT!
12 messages in this thread
We have a client who has rendered out 3800 TGA frames complete with
Aplha Data, ready to do a compositing Video Post. The problem
is…Each of the TGA pics has a white background, and when composited
onto another background (Via Video Post-Queue Alpha) , the white
shows up in a semi transparent state resulting in the scene looking as
if it is viewed through tissue paper.
I have re-created this by rendering the Alpha scene in TUTORIAL 22
with a grey background (lum=180) and compositing it onto the
lowdunes.GIF. The result is that the white is overlayed onto the
lowdunes.GIF as semi-transparent. The alpha data appears to be
correct (ie totally clear where the white background is) but the
white still shows up.
If you render the meshes with ALPHA SPLIT and then use the split alpha
TGA as an Aplha Mask, The white background becomes completely
transparent (the desired result!) Any help here as his job is almost
due, and re-rendering all the frames obviously is out of the
question. He wants the white background to disappear completely when
composited as the Alpha data should tell it to. Thanx in Advance
Michael – Somebody radically misunderstood the concept of Alpha. The frames
should never have been rendered over a white background. This type of matting
is not for use with Alpha images but with images where you cannot use alpha
because they don't support it, ie: they're not 32 bit. The best you can hope
for is a luminance key because of the way this was rendered. Try using RGB Mask
with Intensity and turn Negative ON. This is so backwards however. Because
Intensity is usually used for Black not White.
The other factor is that if you had just rendered the images without a white
background you would have saved yourself alot of space on your hard disk.
Next time all you have to do is render without a background and turn Alpha On.
Try experimenting some with VP rendering images and compositing them over a
background.
John:
Good answer! But because I'm picky: (who, me? <g>)
>> The other factor is that if you had just rendered the images without a
>> white background you would have saved yourself a lot of space on your hard
>> disk.
An uncompressed Targa would obviously be the same size. A compressed Targa
looks ahead to see how many pixels are the same color, and compresses them and
adds the number of pixels of that color.
Whether the background is black, white, or magenta, the files will shrink to
about the same size! <g>
Greg Pyros
Greg – Be picky! Got to keeps these things straight. <g>
-JE
The images were rendered on a white background because the client wanted to see
how they would look against white, as his artwork (to be supplied later) was
predominantly white.
They were rendered on white as the manual stated that any non-3d objects ie
backgrounds would come through as clear…
BTW its weird that if you strip out the alpha channel and use it as an alpha
mask, it comes out perfectly clear!? The use of alpha seems a bit inconsistent.
Thanx for the help, I will don my armour and go and see the clien today with
the news…
See ya
Can you run just those images through video post and save alpha channel
separately, and then use those alpha files as the alpha mask for the real pass
through? LAM
Gooooood Idea!, It does leave a bit of white around the edges (the
anti-aliasing) but it may have to do
Thanx
Mike – I'll try out the approach you used, it does seem curious that by
splitting alpha and rendering with a white background the white become
transparent. Alpha as I have described it however is very consitent to the
point I take it for granted ie, it works every time!
Hope all goes well.
Regards – JE
Ummmm, thats not quite it. If you do not split alpha, but render
with alpha on (with a white background) and use queue alpha in video
post, you get transparent white.
If you split alpha, and apply alpha channel as a mask in video post, you get
clear (ie invisible) white
Weird huh?
Michael – >> If you do not slit alpha,
Everything you state makes sense to me. My point was that the scene should not
have been rendered with a white background in the first place. It should have
been rendered without a background with Alpha On. No need to split Alpha that I
can see.
If one wanted to see the scene or specific images over a white background then
just composite them that way later.
Then when you want to composite them over a different background its no
problem.
Its important that if you are going to render seperate elements
because they might be changed to make sure you've got Alpha ON and
that they go to a seperate file. This affords you maximum flexibility
later on.
Are you saying that you haven't resolved how to do a luminance key
into the white?
The beauty of VP and alpha and alpha mask and RGB etc. is that there
are alot of possibilities. Unfortuneately it appears this is working
against you at the present time. I'm not sure what's hanging you up
and so I can't help, other than what I've told you already.
Drop me a line with more complete info and we'll see what needs to be
done and get this resolved. Then if you have any other questions, we
can take care of those later.
Greg Pyros mentioned an Alpha IXP a couple days ago that would
strip the alpha info into a separate file, so you might want to ask
him about this. Photoshop and Pstyler 2.0 can also separate the
alpha, but only manually one at a time (3800 frames = 3 weeks?) so
thats not a good idea. Also, If I read Gary's response correctly to
your last message, If they have access to it, then they can just
composite the existing frames in R2.
No, I tried release 2 and it does the same thing.
Thanx