Ways to get rid of Aliasing?

Uwe Lansing

Uwe Lansing

Veteran
Ok, the way things look the 7d seems to suffer a lot of aliasing in 720p50/60 mode. Is anbody out there who knows a solution for that problem? Be it in form of a filter, a workaround in post or whatever.....
 
Shoot with softer lenses? Pro-mist? Double fog? There's an anti-alias filter in After Effects, but generally it'll degrade the image. Just had issues with aliasing on a kids show I work on, the ultimatte had aliasing issues throughout several episodes, had to reperform the backgrounds for every shot.
 
hermmermferm said:
...There's an anti-alias filter in After Effects, but generally it'll degrade the image...
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Just took a look at ae cs4 - i couldn´t find it. What´s the exact name? There is an anti-alias filter in pp cs4. i gave it a go yesterday but without success...

@ plasmasmp

yes, this would lessen aliasing a bit. I tried out a slight gaussian blur and afterwards somewhat of sharpening without a good result...
 
I think neatvideo looks great but the anti jaggie stuff was due to specific solution to d90s pixel binning footage from Lee Wilson.
 
My understanding is that there is no real solution to the aliasing problem, even in post. There are in-camera workarounds:

1. shallow DOF - fewer things in focus mean a lower probability of artifacts. Of course, if your subject is aliasing, that doesn't help. So..
2. shoot soft - either a little off focus or with softer lenses.
3. provide a filter - experiment with some sort of diffusion filter to soften the image somewhat

Until it is understood exactly what process is used by Canon to create the image, any attempt to fix the artifacts is guesswork. All we know now is that it apparently bins in "groups of six". The whole line-skipping thing has been, to the best of my knowledge, repeatedly denied by Canon reps.
 
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I just made a google search and found some interesting stuff. Obviously it isn´t possible to get rid of aliasing if it is already there. So the post production way seems to be not very successful. But in several postings they recommend "Diffusion Filters". Take a look at these links:
http://www.dvinfo.net/forum/canon-eos-5d-mk-ii-hd/140442-aliasing.html
http://www.dvinfo.net/forum/canon-eos-5d-mk-ii-hd/412718-upping-anti.html
http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/filter-diffusion.html
http://www.vimeo.com/6644964
http://www.maxmax.com/hot_rod_visible.htm
 
I read a long thread somewhere (guess it was cinema5d forum) about aliasing problem. People have been trying a lot of softening filters on 5d2 (including dedicated anti-moire filters like Caprock) with no significant success. Such optical low-pass filter has to be designed for given sensor resolution - otherwise it either does very little in terms of reducing aliasing or severely degrades the MTF (sharpness)...

Also, I don't believe any digital filter can successfully reduce aliasing in post. There's no real way to tell the aliasing from the lower-frequency image component (I mean real image here).

As Michael suggested - shallow DOF and shooting slightly off-focus might help. Also, aliasing is typically much less apparent when camera is static
 
I thought the 7D shoots frames progressively?....How is there aliasing? Or does this have something to do with the codec?
 
Jean Dantes said:
I thought the 7D shoots frames progressively?....How is there aliasing? Or does this have something to do with the codec?
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Aliasing occurs in the 7D footage because it uses a sensor with a resolution of 5184 × 3456 to produce an image with a resolution of 1920 x 1080. Somewhere in the process of creating this lower resolution, pixels are "binned" - combined (see Barry's post below) - and the rest of the image pushed back together. There seems to be little done to cover up this tactic in terms of anti-aliasing processing in camera. That (along with some other factors like the optical low pass filter) leads to the jagged edges.

Unfortunately, Canon has not told us exactly how the camera does this. If we knew exactly what process was used to scale the image down, it is likely an algorithm could be created for a plugin to repair at least some of the artifacts reliably.
 
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"binning" doesn't mean they're thrown out, it means they're combined.

"binning" in British terms would mean, yes, throwing them in the bin, but that's not what the term means when applied to an image sensor. It means that multiple pixels are combined and treated as one big superpixel.
 
Barry_Green said:
"binning" doesn't mean they're thrown out, it means they're combined.

"binning" in British terms would mean, yes, throwing them in the bin, but that's not what the term means when applied to an image sensor. It means that multiple pixels are combined and treated as one big superpixel.
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Thanks for correcting me, Barry. I've corrected my post.

Lots of learning for me today...
 
Tim Joy said:
How about just adding noise/grain? Seems to be working for me, and it also reduces banding.
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Can you put up a few examples - a scene with grain and the same scene without? And maybe put a few stills so we can see it in full resolution uncompressed by vimeo or whatever.
 
heres a case from a bridge i filmed...
bridgeslice.JPG
the highlighted broken red line has gaps that move through the footage...the line is actually a complete red line...this is the worst case I have found, some other footage of wavy roof tiles is bad but they are a long way away.
Could be an idea to mask then blur worst areas in ae.
 
Michael Olsen said:
Aliasing occurs in the 7D footage because it uses a sensor with a resolution of 5184 × 3456 to produce an image with a resolution of 1920 x 1080. Somewhere in the process of creating this lower resolution, pixels are "binned" - combined (see Barry's post below) - and the rest of the image pushed back together. There seems to be little done to cover up this tactic in terms of anti-aliasing processing in camera. That (along with some other factors like the optical low pass filter) leads to the jagged edges.

Unfortunately, Canon has not told us exactly how the camera does this. If we knew exactly what process was used to scale the image down, it is likely an algorithm could be created for a plugin to repair at least some of the artifacts reliably.
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Ahhhh I see. Interesting, I didn't know that. Well, I guess the good news is that it is software, not hardware, related. Though I think the 50P/60P are quite good, hopefully there will be a firmware update that will make them even better.
 
Jean Dantes said:
Ahhhh I see. Interesting, I didn't know that. Well, I guess the good news is that it is software, not hardware, related. Though I think the 50P/60P are quite good, hopefully there will be a firmware update that will make them even better.
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Eh...my understanding of this really isn't the best but...

..the problem may be hardware related. It is possible that this rather simple way of scaling down was introduced because of a lack of processing capability in the hardware. After all, we are essentially dealing with hardware optimized for taking photographic stills.
 
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