[Bf-funboard] OSA/MBlur..Odd/Even Upper/Lower fields... sky/premult/key

Luke Wenke bf-funboard@blender.org
Mon, 6 Oct 2003 03:35:38 +1000


OSA/MBlur
I think OSA and Mblur should be arbitrary and independent... at the moment
mblur is limited to 16.... when I have a lot of movement I want to increase
that.... and what I end up doing is using the animation buttons to slow
things down (and create extra time for more Mblur)... the IKA skeletons
don't seem to go at the altered speed though. And sometimes I want to have
mblur set high, but osa set low... e.g. to smooth the envmaps a little
(without osa, they're based on one sample per frame).
And maybe OSA should be called "AA" (anti-aliasing) instead since I think
that is more widespread and well-understood.

Fields
I've been working with fields a lot and from what I've read, odd and even
fields are very ambiguous. The standard thing these days is to call it
"upper field first" (or upper) or "lower field first" (lower). As far as I
can recall, in blender, the even output (default) is equal to lower field
first, and odd output is upper field first. The reason why odd and even is
arbitrary (and varies from program/device to program/device) is because it
depends on how you number the fields. If you number the top field 0, then
that field is even. If you number it 1, then that field is odd. As far as
the input movies go for textures, StField has no tooltip at all. I think it
reverses the fields and when it is enabled it is lower/even and when it is
disabled it is upper/odd.... I'll probably recheck that sometime. I think
Fie/Ima is wrong ("Number of fields per rendered frame"). e.g. I've got a
movie with fields loaded, which has about 1800 frames. I've set the frame in
blender to 700 and when Fie/Ima is 2 (default) the current frame is 700.
(usually... blender seems pretty buggy in that area)

(Remember that Blender's animation frame is 700)
Fie/Ima Current Frame
1           1399        (2/1 * 700)
2           700          (2/2 * 700)
3           467          (2/3 * 700)
4           350          (2/4 * 700)
5           280          (2/5 * 700)
6           234          (2/6 * 700)
7           200          (2/7 * 700)

In the last example, blender's frame was at 700, but the current frame in
the input video is only 200. It was set to 7 "fields per rendered frame"....
Actually there are 200 pairs of input fields per 700 output frames.... or
7/4 output frames per input field, or 7/2 output frames per input frame.
To fix this, it could be replaced by this:
Fie/Ima Current Frame                     Img/Frame (rendered images per
frame) or Img/Field
1           1399        (2/1 * 700)         0.5
1
2           700          (2/2 * 700)         1
2
3           467          (2/3 * 700)         1.5
3
4           350          (2/4 * 700)         2
4
5           280          (2/5 * 700)         2.5
5
6           234          (2/6 * 700)         3
6
7           200          (2/7 * 700)         3.5
7
(Basically I'm saying the description is backwards, but it would probably be
more normal to be Img/Frame rather than Img/Field so you can easily see the
change in framerate... e.g. 3 Img/Frame means the output is 3 times slower
than the input)

sky/premult/key
I think "key" should be renamed to the standard name "straight". The tooltip
could mention "(unmatted)" at the end. And the tooltip for premult could
mention "(matted)". Sky could be renamed to "show sky". The tooltips for
premult and key sort of imply that something is happening to the alpha
channel... but actually I think the alpha channel is identical in both
cases... it is just the rgb rendered image that changes. In the "straight"
one, the colours are unaltered. In the "premultiplied" one the colours are
multiplied by the alpha channel.

- Luke.