Problem with Alpha in PNG files: Wacom Tablet - Photoshop ok / Vegas not...

FuTz wrote on 4/5/2005, 12:12 PM

I'm doing this rotoscopy project and what I did is export frames from video into several pics (PNG, using the "render image sequence" script) so I can touch-up each frame within Photoshop.
I'm using the Eraser. And that gives me problems when I import these files back into Vegas:
-either the "feathered" part of the Eraser strokes are partly white with no "softness" from transparency to this white "outline" that
appears out of nowhere when back in Vegas (previously perfect in Photoshop)
-either I get white dots in Vegas if I use a "hard edge" Eraser in Photoshop.

Reminds me a little bit of what happens with transparency in Photoshop when you "save for Web" and use PNG instead of PNG24. With PNG24 (bits) you'd get a perfect feathering while not at all with PNG.

The settings when I'm back in Vegas: I right-click the event that contains the touch-ups (the Eraser strokes - frame by frame) and go into Media tab then put alpha to Premultiplied.
This track is the Top Track and I'm trying to insert another image via another Track just under into the "holes" created by the Eraser. Hence the importance of having nice, perfect "gradients"/"feathering" on the top track, which I don't get. Instead, I just get White artifacts instead of a smooth feathered line between the two images (tracks).
I tried the whole bunch of alpha styles inot the clip properties (right-click I just told you about) and I also tried every combination I could with compositing (relation between the two tracks, "Parented-childed" or not)

Is there any solution?

PS : I did try the Eraser with Wax too but I realised you have to key both IN and OUT points for every single frame to animate it ; you do the maths...

Comments

B_JM wrote on 4/5/2005, 12:27 PM

1. using render as image script is slow compared to frame serving and rendering as frames outside vegas - but ...

2. make sure in PS you are not working over a white background when using antialiasing is on. Make sure that the intermediate colors created when antialiasing blend into your background color.

3. try using tiff instead for better properly stored opacity and transparency.

FuTz wrote on 4/5/2005, 12:57 PM

... I figure out a black background (maybe mid-gray?) instead of the standard "checkerboard" would be better?

Also, since I'm doing a whole 4 min. videoclip, rendering each frame in TIFF would suppose having a 800Go hard drive to store all this data, no ?

B_JM wrote on 4/5/2005, 1:22 PM

The general rule for 24 Bit RGB uncompressed TIFF images is, MP x 2.93 = approx MB. To get the MP (megapixels), simply multiply the pixel dimensions and divide by 1,000,000.

Embedding a color space profile in the image can slightly increase the file size. Saving layers, thumbnails, etc.. in the TIFF file can significantly increase the file size.

D1 NTSC = ~1meg per frame / 7200 frames = 7.2GB

720P = ~2.7meg per frame / 5760 frames = 15.5GB

RafalK wrote on 4/5/2005, 1:28 PM

I don't think you want to use the "save for the web". Saving for the web reduces the color pallete to only the web safe colors. Maybe this is what's causing the problem.

FuTz wrote on 4/5/2005, 2:50 PM

I am not saving for web right now. I use the file provided by the script ; a PNG file.
I did try though, just to have a look at what 's the result and saving to PNG24 improved the transparency if I go with Straight (Unmatted) int the clips prefs...
But I'd have to convert nearly 8000 files.

bakerja wrote on 4/8/2005, 2:03 PM

My experience is that saving in native photoshop format for transparency works best for me. I have experimented with tiff and png and find that psd works best.

JAB

jeremyk wrote on 4/9/2005, 11:51 AM

I don't know if this is your problem, but for PNGs from Photoshop I have to set the alpha channel property in Vegas to premultiplied and set the background color to white (black is the default). Otherwise I get the white fringes I think you're talking about.

Jeremy

FuTz wrote on 4/10/2005, 7:45 AM

I got it... and forgot about this way to go for the clip. No rotoscopy this time.
Explanations... please, don't laugh...

I wanted, like I said, to make some rotoscopy. But I did not want to have to draw 8000 frames by hand. So I thought: just render a track at "half NTSC" setting (in fact, I tried 15fps from the start) and "do your job" on this track so you'll have 4000 frames instead of 8000 to work on. The flicking of picture wasn't an issue, in fact it would "suit" the look... "animation look"...
Only, I placed a 29,97 clip on the second track ( Detail: I was in fact *erasing* frame by frame, not *drawing*. So I can see the track #2 "show through" the first one.)
The project Prefs were set at "29.97" as the clip on track 2 had the best rate and I didn't want to go under that standard.

Only, now what happens when you do this is that the track with 15fps (or half NTSC) will be "extrapolated" to fit the project OR the second track (yes, I tried setting the project at 15fps or "half NTSC and the results were the same). What you get then is a lot of "overlapping frames(?)", HENCE these white artifacts which are in fact the "ghosts" of the preceding or following frames according to the track that's set at 29,97.

So what I had to do was render the whole thing at 15fps, put my rotoscopy track at 15fps on top, set the project Prefs at 15fps and do my work. EVERYTHING at the same rate (here: 15fps / half NTSC).
AFTER that, I would render at 29,97 and get nice results.

Only, after the tests, it didn't give the results I was expecting. At all. So I simply dropped the idea... : (

In another post, somebody asks what we were doing this weekend : me? After this INTENSIVE crash course in "project Prefs vs. track prefs vs. render specs 101", I did NOT touch Vegas. Ha! ; D

And thanks everybody. I tried a few things concerning Photoshop and practically all your tips worked concerning the quality of the alpha channel...
Cheers!