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View Full Version : How do you get rid of aliasing?!



Filmkid2003
07-09-2010, 09:14 PM
I've been shooting film footage with the GH13 with bitrate settings of 50,52,70 and 24/60i and looking at the footage on my 47" LCD HD T.V. while editing in Premiere Pro CS5, I'm noticing a lot of jagged edges wherever there are horizontal slanted lines! I don't see any jagged edges on the vertical lines (edges of objects) though. The vertical lines in the image are jaggy-free. Is there any way to correct this via firmware or in post? What causes this effect?

philiplipetz
07-11-2010, 05:42 AM
I've been shooting film footage with the GH13 with bitrate settings of 50,52,70 and 24/60i and looking at the footage on my 47" LCD HD T.V. while editing in Premiere Pro CS5, I'm noticing a lot of jagged edges wherever there are horizontal slanted lines! I don't see any jagged edges on the vertical lines (edges of objects) though. The vertical lines in the image are jaggy-free. Is there any way to correct this via firmware or in post? What causes this effect?
try changing your deinterlacer-pulldown removal program.

Barry_Green
07-11-2010, 07:39 AM
Read the article on Aliasing in the "articles" section, it explains what causes it.

As to how to get rid of it -- nobody likes the answer (but that, of course, doesn't change the validity of the answer). You have to avoid giving the camera too much detail. So that means using a softer lens, throwing more things out of focus, or using the appropriate caprock anti-moire filter, or stopping down to f/22 or even further to introduce enough diffraction to filter out the excess detail that causes aliasing.

Here's the rock-hard fact with all DSLRs: if it's in focus, it's aliasing. Maybe in a way you can notice, maybe not, but it is -- it doesn't have a choice about it, it must alias. That's the way DSLRs get their high sharpness. So you'll notice that in most of the "beautiful" footage people post, there's a whole lot that's not in sharp focus, all the background is in soft focus and frequently lots of foreground is too. The effects of aliasing are most noticeable on hard transitions and square lines, so if you want to do a wide deep-focus shot of buildings, that kind of shot is pretty much impossible to pull off on a DSLR without significant aliasing artifacts. In a case like that, the best hope you have is to NOT MOVE the camera! Because aliasing mainly reveals itself in motion.

Filmkid2003
07-11-2010, 12:34 PM
Thanks, guys. I noticed when I shoot in native 24p on my Gh13, I don't get the jagged edges at all. But, I have some footage that I shot in 24/60i that has a lot of jagged edges and now I have to intercut that with the native 24p footage. Phillip, how do I deinterlace/pulldown removal in Premiere Pro CS5? Does anyone know? If I go to "Interpret Footage" in Premiere CS5, the "24p Pulldown Removal" is all grayed out and won't let me click on it! Also, if I click on "Always Deinterlace", nothing happens. The jagged edges are still there! Can someone that is familiar with Premiere Pro CS5 please help me with this? Thanks.

rambooc1
07-11-2010, 02:09 PM
Actually you can use aliasing as a focusing guide. When the image is in perfect focus in the EV, you can see small aliasing on the horizontal lines. When you see this your image (at that depth of focus) is perfectly focused. ....hehe.

At that point you can decide to defocus slightly or leave as is and apply a small blur in post.

This is very handy for us older gentlemen with eyesight not so good anymore.

R

Svart
07-11-2010, 02:13 PM
I think he's seeing the interlacing, not aliasing. I had a friend who was editing my files from 24/60i and he kept complaining about all the aliasing, which I never saw.

Once I looked at his finished work I knew that he had never de-interlaced and done pulldown removal. He *thought* he had but he had not, he just transcoded it without pulldown removal/deinterlacing. Once we did those, it looked great.

Barry_Green
07-11-2010, 02:37 PM
I was just gonna say that. Sounds like he's seeing interlaced artifacts rather than actual aliasing.

Cavemandude
07-11-2010, 03:32 PM
Guess that proves that Adobe Premiere CS5 is not doing the pulldown properly which is not surprising since no other software has been able to pulldown GH1 1080 24/60i video correctly either including Edius. Most people don't notice the interlaced edge artifacts.

That is the best way to test it now is by using Ptool, shoot one video with the 24p option not clicked and another with it clicked and do a comparison in a 24p timeline.

Randy

Filmkid2003
07-11-2010, 03:38 PM
Yes, you guys are correct. I am seeing interlace artifacts. Sorry, I got that mixed up with the term aliasing. Now, can someone kindly give me the proper steps on how to fix it in Premiere Pro CS5 please? Thanks.

Cavemandude
07-11-2010, 03:42 PM
You'll need to create a new file for each video clip to remove the pulldown before loading it into Premiere using software such as Neoscene.

Randy

Filmkid2003
07-11-2010, 04:37 PM
So, the jagged edges have to do with removing the pulldown? I thought the jagged edges had to do with the footage being interlaced?

Cavemandude
07-11-2010, 04:54 PM
Which has to do with pulldown, it's all related.

Randy

Filmkid2003
07-11-2010, 05:03 PM
Oh. Apparently, when I import my GH1 clips into the Premiere Pro CS5 AVCHD 1080/24p timeline, it automatically removes the pulldown because when I go to "Intepret Footage" the "Remove 24p Pulldown" is grayed out and I can't click on it. I read in another filmmaker forum that the reason it is grayed out is because Premiere CS5 automatically removes the 24p pulldown. ???

Cavemandude
07-11-2010, 05:14 PM
You can word it however you want but that won't fix the problem inside of Premiere.

Randy