What is half frame resolution?
Pete
Can anybody tell me what 1/2 frame resolution actually is?
I understand full frame PAL is 704h x 576v
ie dimensional aspect ratio = 4h:3v pixel ratio= 4h:3v
However, I see (from my RR manual) that 1/2 frame is 352 x 576
Can anybody describe to me what this means
ie is the V resolution still 576 and if so doesn't this mean that the
dimensional aspect ratio has become 1.8h 3v
I'm asking this because when I work in Premiere with 1/2 frame clips,
things are standing on their side eg the sizing boxes in the image
pan dialogue box.
I'm struggling to troubleshoot this because I don't have a fundamental
understanding of what 1/2 frame is.
Cheers
Pete
Mark H
Pete wrote in message <35839409...@news.demon.co.uk>...
>Can anybody tell me what 1/2 frame resolution actually is?
>
>I understand full frame PAL is 704h x 576v
>ie dimensional aspect ratio = 4h:3v pixel ratio= 4h:3v
>
>However, I see (from my RR manual) that 1/2 frame is 352 x 576
>Can anybody describe to me what this means
Although this is 1/2 frame, it is interlaced, ie there are two "fields" in
each frame, the capture program captures this as one frame, but it is really
two,
Sorry if I'm not to clear here!
>ie is the V resolution still 576 and if so doesn't this mean that the
>dimensional aspect ratio has become 1.8h 3v
No, because there are two vertical fields, so divide this no. by 2
>
I'm asking this because when I work in Premiere with 1/2 frame clips,
>things are standing on their side eg the sizing boxes in the image
>pan dialogue box.
Which premiere ver have you got?
4.2 displays image pan properly, If you have captured at 360x540 you can
change the output option to single field and you will see the right ratios,
and when making movie it will be correct. This is important when using
scrolling titles etc.
>I'm struggling to troubleshoot this because I don't have a fundamental
>understanding of what 1/2 frame is.
>
Please post again if I have not explained properly.
I also went through lots of grief trying to understand this at first. Good
luck.
>
>
>
>
>
Tom Clune
Pete <pem...@pemitch.demon.co.uk> wrote in article
<35839409...@news.demon.co.uk>...
> Can anybody tell me what 1/2 frame resolution actually is?
>
> I understand full frame PAL is 704h x 576v
> ie dimensional aspect ratio = 4h:3v pixel ratio= 4h:3v
>
> However, I see (from my RR manual) that 1/2 frame is 352 x 576
> Can anybody describe to me what this means
>
>...
There are many problems in getting video from a capture card to the
computer, and one of the most substantial of those is the amount of data in
an image. There have been various choices made on how to lower the frame
data rate in addition to using compression algorithms. For example, other
than the MPEG-I compression, the decimation of data itself from 704x480 to
352x240 achieves a factor of four reduction, just by throwing away 3 out of
4 pixels. However, many people are no longer satisfied with this draconian
decimation -- they want to have a full frame compressed.
One attractive compromise to doing no decimation is to digitize the video
raster at a slower rate. That is, if the A/D converter samples for twice as
long a time, you will end up with a raster line that contains 352 pixels
instead of 704. Since video tends to be noisy, getting a cleaner A/D value
for each pixel has a lot to recommend it, including that noise tends to
lower the efficiency of compression algorithms (the rule of thumb is that
the noise decrease would be the square root of the ratio of the sampling
intervals, so you would lower noise by about a factor of 1.41. If you had
nearly six bits of good data at thre original rate, you would achieve over
seven bits with the longer integration time -- if the noise was truly
Gaussian). Since you really aren't getting 704 good 8:8:8 bit pixels from
video anyway, this approach largely preserves the data that you can get
with the higher sampling rate, decimates the pixels by a factor of two,
improves the efficiency of your compression algorithm, and -- once the
display algorithm stretches the data set back to 704x480, presents an
pretty-much indistinguishable image from the full 704x480. You can't do a
similar thing in the Y direction with the same effectiveness, because every
other line in video is a sixtieth of a second off in time from its
neighbors, and that is massively "further" than the tempoal distance
between pixels on the same raster line.
I am not familiar with the Rainbow Runner in particular, so I can't say
with complete confidence that this is exactly what they are doing. However,
this approach is widely seen as an attractive new approach to decimation
that preserves the data by increasing the z-axis resolution at the expense
of the x-axis, providing a "wash" for the inforamtion content and achieving
a factor of 2 reduction in board traffic.
The problem you are having with display sounds like Premier does not
recognize the "half D1" (a common way of referring to this format) data
set. You may need to get a newer version of your NLE. Hope this helps.
--Tom Clune, Data Translation, Inc.
Pete
>> Can anybody tell me what 1/2 frame resolution actually is?
>>
>> I understand full frame PAL is 704h x 576v
>> ie dimensional aspect ratio = 4h:3v pixel ratio= 4h:3v
>>
>> However, I see (from my RR manual) that 1/2 frame is 352 x 576
>> Can anybody describe to me what this means
Many thanks to all who posted and mailed me answers to the above
I think I've grasped it now. My understanding is as follows
PAL numbers
Vertical number of capture samples:
full frame resolution = 576 half frame resolution = 576
Horizontal number of capture samples:
full frame resolution = 704 half frame resolution = 352 (this 352
is then interpolated to 576 via software, thereby maintaining the
4h:3v dimensional aspect ratio)
Cheers Pete
kmh
>>Horizontal number of capture samples:
full frame resolution = 704 half frame resolution = 352 (this 352
is then interpolated to 576 via software, thereby maintaining the
Full frame for PAL is 768x576