#Digital Generation Loss
13 messages in this thread
Bruce,
I am hoping you might be able to supply an answer to this. Isn't a freeze frame
on either the MX-50 or the Toaster a digital picture? And if it is digital,
doesn't it keep the same quality no matter how many generations it goes
thorugh?
Well, I have noticed that if I take a scene from an original video tape and
freeze it on the MX-50, it looks as good as the original tape. Then I send it
to the Toaster and store it as a framestore. It is now starting to loose
quality. Then back to the MX-50 for another freeze and finally back to the
Toaster for a final freeze. By now, the picture is starting to get muddy. How
come?
Fred
Fred, There WOULD be no generation loss if you kept the image digital. Every
time your ping ponging it , it it being converted to an NTSC video signal. If
you make a copy of a framestore file from one directory to another in the
computer…no loss……it's 1s and 0s.
Regards, Gary
Gary has it right: every time the video gets converted from analog to digital
and digital to analog, it suffers losses. Actually, the biggest losses come
from the analog circuitry itself, things like buffer, filters, converters, and
cabling. Eventually, it'll all go digital and we won't have THESE problems
anymore – we'll have brand new ones. 🙂
Bruce
Fred,
ALSO…Aside from the issues that Bruce brought up, you have the image
degradation brought on by saving the image as a framestore. Newtek uses a
compression scheme on those files so that they will load more quickly and take
up less space on the hard drive. Several saves of the same image will show a
dramatic loss in qua;lity. For best results, take your freeze image into Tpaint
and save as RGB. This will result in larger file sizes but much better image
quality.
Frank
The compression on framestores is not what causes the image quality loss,
rather it is encoding the image to NTSC color ranges. A frame grab from
video can be saved as a framestore without appreciable loss, and saving it
as RGB from paint won't help. With RGB images generated by lightwave, a
scanner, etc. the framestore format should be avoided as you suggest.
I agree with Frank. I know if you draw a rectangle filled red, save it as
framestore and bring it back, save it few more times, ther's lot's of
artifacting begin to show up, lok like black shaddows. a fill with red again
seems to clear most of them up, and thne again starts artifacting. Saving in
rgb i noticed that this condition is not nearly as dramatic as in framestores.
that's my 3 cents. george
George,
Aki's right,
The reason it keeps "artifacting" is that by resaving as a framestore, you
are video-encoding an already encoded image. Saved RGB's should never show
"artifacting" from the original (assuming your original was RGB, if your
original was a video grab, you are already starting with a video image and
can see NTSC artifacts).
JG
Back home eh. Tanned and well rested I hope.<G>
jmb
Well rested – No.
Tanned – a bit.
JG
A real WORKING vacation.
Glad your back.
jmb
You have sort of made my point. The red square you drew was done in RGB,
by paint. It was encoded into NTSC when you saved it. That process is
LOSSY. The red may have been an illegal color for video, which would
possibly introduce artifacts when it was corrected/encoded. When you
re-loaded it, it was decoded from NTSC to RGB, which does not recover the
spatial color resolution lost by encoding, or restore lost saturation. If
you save it again, you lose some more… etc. The generation loss comes
from the RGB->NTSC encoding step. If you grab a frame from video and save
it as a framestore, you won't have any loss. If you bring it into paint,
it will be converted to RGB, and if you re-save the framestore you could
get some loss, though not as much as you would from an RGB original, which
had so much more to lose in the first place. Once you go into paint,
saving as RGB will avoid all generation loss, as RGBs don't change at all
with loading/saving.
Aki,
Thanks for the info, but I must repectfully disagree with some of what you said
with regard to loss of image quality in saving framestores. There is a dramatic
difference in the quality of framestore images from previous versions of the
Toaster Software. There is also a corresponding difference in file sizes. It
would be difficult for me to accept that there is no correlation between these
two events. Any comment?
Frank
The file size difference is due to a non-lossy compression of the lines in
the IFF framestore image (the same run-length line compression used in IFF
images since 1988). In toaster 2.0, paint saved framestores with this
compression on, but the switcher saved them w/out compression (for 722k
files every time), for faster loading. I believe the latest switcher
saves framestores with compression. I can accept your claim that
different versions have different quality, but the compression/file-size
issue really isn't related to the quality except insofar as the compressed
framestores had been converted to RGB, then re-encoded and saved as
framestores from paint (see previous post).