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detergent
12-08-2009, 03:29 AM
As it was pointed out in some threads and some very informative articles (Barry Green) on this forum, the 7d doesn't really produce 1920/1080 resolution.

Question is: what is the actual (spatial) resolution produced in 1080 24p mode?

Is downsizing to 720 a good way of getting rid of aliasing? To my eye, it starts looking pretty flawless when reduced to a quarter (960/540).

morgan_moore
12-08-2009, 10:09 AM
6-800 lpi ?

S

stephenvv
12-09-2009, 12:20 AM
Note - it does not produce 1080p on rez chart but what Barry and others refer to as "false detail" can be very pleasing to the eye when shot well and aliasing not a factor.

1080p can look wonderful and sharp on the 7D, even with wide shots but you have to control aliasing. Downsizing does not help aliasing directly - could make it worse or better depending on method.

I've got 7D footage that looks higher rez at 1080p then most HD cameras out there except maybe EX1.

If you read the comments on Prolost about Barry's article, you will see knowledgeable disagreement about the "false detail" on VDSLR's - personally I see resolution variance depending on the angle of high contrast lines to thee sensor.

Bottom line - if you know the limitations of the aliasing/moire issues, you can get wonderful 1080p footage that holds up to critical viewing. Barry's article is very helpful and lots of us have posted sample footage of how to control aliasing.

Only lovers of very smooth video (which others fine soft) may not like VDSLR footage in general. But I love it - and the non-techie spouse and friends do as well. Personal taste in imagery is much a factor here.

detergent
12-09-2009, 09:26 AM
Thanks Stephen,

My understanding was that downsizing is actually increasing the sampling density relative to the image ( so more samples per frame) - but this doesn't eliminate or reduce aliasing?
In the discussions that followed Barry's article I came across a statement that the resolving power of 7d in 1080 24p mode is in fact 1150/650 - which is less than 720p. Would that be the actual (sampling) resolution of the CMOS - resulting after the pixel binning process or the resolving power past "up scaling", sharpening and antialiasing filtering?

Anyway, my concluding question is: how can I downsize to 720 and get the best. Simply scaling down in After Effects is a good method?

Thanks.

Michael Olsen
12-09-2009, 03:42 PM
Thanks Stephen,

My understanding was that downsizing is actually increasing the sampling density relative to the image ( so more samples per frame) - but this doesn't eliminate or reduce aliasing?
In the discussions that followed Barry's article I came across a statement that the resolving power of 7d in 1080 24p mode is in fact 1150/650 - which is less than 720p. Would that be the actual (sampling) resolution of the CMOS - resulting after the pixel binning process or the resolving power past "up scaling", sharpening and antialiasing filtering?

Anyway, my concluding question is: how can I downsize to 720 and get the best. Simply scaling down in After Effects is a good method?

Thanks.

Hi...erm, detergent.

A general note to begin things. To the best of my knowledge, CMOS (and CCD?) sensors are plagued by a similar problem - a general reduction in real resolution (about 25%, actually). Even the RED ONE has this problem - shooting at 4K will really resolve about 3K. It's just a matter of all of the various inefficiencies from lenses to OLPFs to sensor designs to compression algorithms.

In general, the solution to your problem has been to shoot as large as possible in as high a resolution as possible and then scale in post as necessary.

Shooting in 1080p mode, the camera resolves almost 720p. Shooting in 720p mode, however, the camera resolves barely 480p or SD. (These conclusions come from Barry's tests).

So to get the very best 720p footage you need, shoot in 1080 and then use software with a good scaling algorithm to scale in post. The caveat here is that, as mentioned, use of scaling in post in addition to the pixel-binning done in camera may introduce artifacts.

stephenvv
12-09-2009, 10:12 PM
Anyway, my concluding question is: how can I downsize to 720 and get the best. Simply scaling down in After Effects is a good method?

Thanks.

AE's scaling engine is not bad. Sony Vegas has an excellent scaling engine. Use one that is "smooth" not with sharpening.