Aliasing

Jay Birch · January 21st, 2009, 07:05 AM

A very crude method to use in post... just apply a low amount of blur onto your footage in your NLE.... untill the aliasing reduces to an acceptable level.... then sharpen the footage, if required.

This doesn't work for every shot, but it can do wonders for some footage... and once down to 720p, the sharpness is still very good, without anywhere near the same amount of aliasing.

Worth keeping in mind untill a proper solution is found.

Hunter Richards · January 21st, 2009, 10:59 PM

compressor, with its amazing array of frame controls, offers anti-aliasing as an option. While it doest totally deal with aliasing issues with various cameras, it does make problems much less noticeable.

frame controls: ON

Anti-aliasing: Full strength (100) for the 5dm2

Jon Fairhurst · January 22nd, 2009, 12:53 AM

Filtering in post can remove stair steps on slight diagonals, such as car roofs, but it won't fix aliasing on repeating patters, such as fine patterned shirts, herringbones, and tiled roofs.

Any time that fine patterns cause larger patches of light and dark, your sunk.

By definition, aliasing is the mistranslation of high frequencies into lower frequencies - sometimes VERY low. DC low. That kind of aliasing is there forever. You need an optical filter and (optionally) oversampling to remove aliased patches.

Joe Wentrup · January 22nd, 2009, 11:02 AM

Down this thread it was mentioned that a Tiffen soft #3 would completely quit the aliasing but was too strong to maintain image shaprness. The same poster claimed that al Tiffen soft # 1 was too weak. His guess was, that the #2 would be the perfect solution.

I wonder if anybody tried that one or a similar filter with good results.

If we find a filter that does the job we have resolved a big problem with few effort. I personally could life even with an image downsampled to 720p.

Anmol Mishra · February 22nd, 2009, 09:08 PM

So far there are 3 solutions
1. Tiffen Soft #2 filter in front of lens
2. Tulle ultra fine mesh
3. Keep the object slightly out of focus so the lack of focus compensates for the aliasing

2. does not seem to work consistently..i.e. It gives an effect but it shows the mesh on closeup, especially over lights.

So far, no one has confirmed Soft #2 filter.

Does anyone wish to add something ?

Mark Hahn · February 23rd, 2009, 04:10 AM

Quote:

Originally Posted by Anmol Mishra

So far there are 3 solutions
1. Tiffen Soft #2 filter in front of lens
2. Tulle ultra fine mesh
3. Keep the object slightly out of focus so the lack of focus compensates for the aliasing

2. does not seem to work consistently..i.e. It gives an effect but it shows the mesh on closeup, especially over lights.

So far, no one has confirmed Soft #2 filter.

Does anyone wish to add something ?

I would personally prefer moire to any of these sharpness reducing solutions. Of course we would have to monitor for moire on every shot and re-setup shots with really bad moire, but that's the way life is.

For example, if a building in the background has a pattern of bricks showing bad moire, then we change DOF, we change focal length, or switch locations until it looks better.

The is no way Canon can fix the moire in the 5D2 without a serious hw fix, and that's that.

Anmol Mishra · February 23rd, 2009, 06:12 AM

When you mean changing DOF and focal length, you are simply creating softness in the image. Isn't that the same as the out-of-focus option mentioned above ?

Jon Fairhurst · February 23rd, 2009, 11:52 AM

Quote:

Originally Posted by Mark Hahn

The is no way Canon can fix the moire in the 5D2 without a serious hw fix, and that's that.

There are two ways to fix the moire - a lower frequency optical filter or a digital filter that reads all of the samples.

The digital filter approach would be awesome, but it would have to deal with three times the data rate coming off the sensor. Maybe we'll see this in a $10k+ video camera. That would compete with the FF35 Scarlet.

The other approach would be an optical low pass filter with 1/3 the resolution of the current filter. A well matched screw-on filter would do the same. The problem is that we'd get a 720p (or so) result, rather than 1080p. Red faces this same problem, which is why their lowest resolution is 3K. A 3K Scarlet should be able to give a true 1080p result without aliasing. That's one of the beauties of RAW. It moves the demosaicing and the digital low pass filter from the camera to the PC.

Joe Wentrup · February 23rd, 2009, 01:18 PM

Still optimistic that a simple filter will be the workaround for now - just hope that the whole footage then doesn't look like softporn...

Jon Fairhurst · February 23rd, 2009, 01:38 PM

Quote:

Originally Posted by Joe Wentrup

Still optimistic that a simple filter will be the workaround for now - just hope that the whole footage then doesn't look like softporn...

Or like a closeup of a 1940s starlet. "All right, Mr. DeMille, I'm ready for my close-up."

That's why we should look at soft filters, rather than, diffusers. I don't know how they do it, but diffusers seem to smear bright light farther than soft. A true optical low pass filter will limit the spatial frequencies, regardless of brightness.

Anmol Mishra · February 23rd, 2009, 07:19 PM

Here is a review of some soft/diffusion filters.
Special-Effects Filters: Diffusion Filters

Reviewed filters are
>>
Hoya Duto, Tiffen FX, Cokin Sunsoft, Cokin Diffuser
B+W Soft Focus 1, B+W Soft Focus 2, B+W Soft Image
>>

There is also a description..

I cannot paste images but the background of an image is compared.
Would anyone care to post on the findings ?

Jon Fairhurst · February 23rd, 2009, 11:37 PM

Nice comparisons. Personally, I like the Hoya filter best for anti-aliasing. It seems to filter everything without adding much glow. That said, I have no idea if the Hoya would be too strong or too soft for our application.

The good news is that Hoya filters are usually pretty cheap. It's definitely worth a try...

Anmol Mishra · February 23rd, 2009, 11:50 PM

Make your own diffusion filter
Why invest in a diffusion filter when you can make one yourself? Here are five D.I.Y. diffusion filter ideas...

* Blow on your lens and let your breath condense there. Quickly press the shutter release before the condensation evaporates--it works surprisingly well.
* Crumple a piece of cellophane, flatten it out, and hold it in front of your lens or secure it there with a rubber band.
* Take a clear or skylight filter and spray it lightly with hair spray, add dabs of clear nail polish, or a spread a thin layer of petroleum jelly (Vaseline) over it.
* Take a clear or skylight filter and use a fine-point black permanent marker to cover the entire surface with tiny dots.
* Stretch taut a piece of black net or panty hose over your lens. Secure it with a rubber band.

Mark Hahn · February 24th, 2009, 12:00 AM

Quote:

Originally Posted by Anmol Mishra

When you mean changing DOF and focal length, you are simply creating softness in the image. Isn't that the same as the out-of-focus option mentioned above ?

You set the focus and depth-of-field so the target object is in focus and the background object with the moire is out-of-focus.

Changing focal length can accomplish the same thing if you change your distance from the subject and change the focal length to get the same framing. Of course this has the problem of the perspective change.

Both changes affect the overall look of the scene though, so I would probably just reset the scene so the object with the moire isn't in it.

My argument for these techniques is simple. I want NOTHING to reduce the sharpness of my target object.

Anmol Mishra · February 24th, 2009, 01:47 AM

Hi Mark. Please bear with me as I try to understand what you are saying.
First, the moire effects only the background. However, the 3-line readout employed by the 5D also effects whats in focus - causing artificial sharpening effects..

So, when we are talking of modifying DOF, are we going to open or close the iris ? So, we go to a higher ISO and we reduce from say f4 to f2.8 or vice versa..

I am unaware of another direct effect on DOF. Here we can maintain focus and focal distance.

What you are talking about is to keep the ISO constant, change the f-stops and refocus to (hopefully) remove the moire artifacts.

Another problem is that the moire may not show in the Live View or external and may turn up on the recording. The recording format is 4:2:0 AND heavily compressed. This causes the moire to look worse.

So we need to record and review the recording on a big enough screen, and then reshoot if necessary..

Hmm! Have to think about that..

Quote:

Originally Posted by Mark Hahn

You set the focus and depth-of-field so the target object is in focus and the background object with the moire is out-of-focus.

Changing focal length can accomplish the same thing if you change your distance from the subject and change the focal length to get the same framing. Of course this has the problem of the perspective change.

Both changes affect the overall look of the scene though, so I would probably just reset the scene so the object with the moire isn't in it.

My argument for these techniques is simple. I want NOTHING to reduce the sharpness of my target object.

January 21st, 2009, 10:59 PM	#32
Hunter Richards Regular Crew Join Date: Mar 2008 Location: Portland, Oregon Posts: 89 Images: 2	compressor, with its amazing array of frame controls, offers anti-aliasing as an option. While it doest totally deal with aliasing issues with various cameras, it does make problems much less noticeable. frame controls: ON Anti-aliasing: Full strength (100) for the 5dm2 __________________ HR\|cinematographer HunterHRichards.com

January 22nd, 2009, 12:53 AM	#33
Jon Fairhurst Inner Circle Join Date: May 2006 Location: Camas, WA, USA Posts: 5,513	Filtering in post can remove stair steps on slight diagonals, such as car roofs, but it won't fix aliasing on repeating patters, such as fine patterned shirts, herringbones, and tiled roofs. Any time that fine patterns cause larger patches of light and dark, your sunk. By definition, aliasing is the mistranslation of high frequencies into lower frequencies - sometimes VERY low. DC low. That kind of aliasing is there forever. You need an optical filter and (optionally) oversampling to remove aliased patches. __________________ Jon Fairhurst

February 22nd, 2009, 09:08 PM	#35
Anmol Mishra Major Player Join Date: Jun 2007 Location: Sydney Australia Posts: 401	Conclusions So far there are 3 solutions 1. Tiffen Soft #2 filter in front of lens 2. Tulle ultra fine mesh 3. Keep the object slightly out of focus so the lack of focus compensates for the aliasing 2. does not seem to work consistently..i.e. It gives an effect but it shows the mesh on closeup, especially over lights. So far, no one has confirmed Soft #2 filter. Does anyone wish to add something ?

February 23rd, 2009, 07:19 PM	#41
Anmol Mishra Major Player Join Date: Jun 2007 Location: Sydney Australia Posts: 401	Comparison of soft/diffusion filters Here is a review of some soft/diffusion filters. Special-Effects Filters: Diffusion Filters Reviewed filters are >> Hoya Duto, Tiffen FX, Cokin Sunsoft, Cokin Diffuser B+W Soft Focus 1, B+W Soft Focus 2, B+W Soft Image >> There is also a description.. I cannot paste images but the background of an image is compared. Would anyone care to post on the findings ?

February 23rd, 2009, 11:37 PM	#42
Jon Fairhurst Inner Circle Join Date: May 2006 Location: Camas, WA, USA Posts: 5,513	Nice comparisons. Personally, I like the Hoya filter best for anti-aliasing. It seems to filter everything without adding much glow. That said, I have no idea if the Hoya would be too strong or too soft for our application. The good news is that Hoya filters are usually pretty cheap. It's definitely worth a try... __________________ Jon Fairhurst

January 21st, 2009, 07:05 AM	#31
Jay Birch Regular Crew Join Date: Nov 2008 Location: Portimao Posts: 49	A very crude method to use in post... just apply a low amount of blur onto your footage in your NLE.... untill the aliasing reduces to an acceptable level.... then sharpen the footage, if required. This doesn't work for every shot, but it can do wonders for some footage... and once down to 720p, the sharpness is still very good, without anywhere near the same amount of aliasing. Worth keeping in mind untill a proper solution is found.

January 22nd, 2009, 11:02 AM	#34
Joe Wentrup Regular Crew Join Date: Dec 2008 Location: Santo Domingo Dominican Republic Posts: 27	Down this thread it was mentioned that a Tiffen soft #3 would completely quit the aliasing but was too strong to maintain image shaprness. The same poster claimed that al Tiffen soft # 1 was too weak. His guess was, that the #2 would be the perfect solution. I wonder if anybody tried that one or a similar filter with good results. If we find a filter that does the job we have resolved a big problem with few effort. I personally could life even with an image downsampled to 720p.

February 23rd, 2009, 06:12 AM	#37
Anmol Mishra Major Player Join Date: Jun 2007 Location: Sydney Australia Posts: 401	When you mean changing DOF and focal length, you are simply creating softness in the image. Isn't that the same as the out-of-focus option mentioned above ?

February 23rd, 2009, 01:18 PM	#39
Joe Wentrup Regular Crew Join Date: Dec 2008 Location: Santo Domingo Dominican Republic Posts: 27	Still optimistic that a simple filter will be the workaround for now - just hope that the whole footage then doesn't look like softporn...

February 23rd, 2009, 11:50 PM	#43
Anmol Mishra Major Player Join Date: Jun 2007 Location: Sydney Australia Posts: 401	Diy filter solutions Make your own diffusion filter Why invest in a diffusion filter when you can make one yourself? Here are five D.I.Y. diffusion filter ideas... * Blow on your lens and let your breath condense there. Quickly press the shutter release before the condensation evaporates--it works surprisingly well. * Crumple a piece of cellophane, flatten it out, and hold it in front of your lens or secure it there with a rubber band. * Take a clear or skylight filter and spray it lightly with hair spray, add dabs of clear nail polish, or a spread a thin layer of petroleum jelly (Vaseline) over it. * Take a clear or skylight filter and use a fine-point black permanent marker to cover the entire surface with tiny dots. * Stretch taut a piece of black net or panty hose over your lens. Secure it with a rubber band.