XL2 image problem

A. J. deLange · February 16th, 2005, 11:06 AM

I think it's been said dozens of times here and elsewhere but it is a difficult subject and people get confused so let me try to summarize. There is nothing wrong with the XL2 with respect to aliasing. Sampled systems are subject to aliasing which appears as moire in a two dimensional image unless the sampled information is strictly band limited to less than one half the sampling rate. Many cameras (especially still cameras) have optical antialiasing filters. The Canon video cameras apparently do not. Thus they are subject to moire but so are most other video cameras. Look at TV (including HD) and you will see moire. There is absolutely nothing that can be done about it except to reduce the spatial high frequency component of your image before it reaches the sensor. This can be done with blurring or diffusing filters. If you want to get rid of aliasing buy a blurring filter (and don't complain about the loss of resolution - you'll lose some). Once aliasing is in it is in forever - it cannot practically be removed though it is possible to mask it in post in some cases.

Per Oellgaard · February 16th, 2005, 03:49 PM

Thank`s Chris and A.J.

I will try to do some shots in the comming weekend,, Denmark is when I´m off my job too Dark in the winterseason.
I will let You know if Your adwise helps on the moire problem.
A.J Thank You for a very concrete answer. I needed that during the discussion on this forum.
I understand that moire is a normal thing. I watch the Olympics too. I see it every time I turn on my TV, even in a very expensive movie produced by the Danish Television (DR), and I accept moire as an intergraded part of making video, but I just think the ammount of moire is much too high with my brand new, in all other parts superlovely XL2.
If it would be in anybodys interrest I have a shot as a very good evidence. I just don´t know how to link it to this page.
Sorry to bring this up again.

Barry Goyette · February 16th, 2005, 05:13 PM

Per

Just to reiterate one of my earlier posts on this subject... quite often the moire you are seeing is more relevant to the viewing device than it is the the camera. The originator of this thread was unable to show us the moire in the image itself because there was none. The higher resolution of the xl2's progressive mode will cause interlaced monitors to produce a moire even when one doesn't exist in the image itself. Such is the nature of moires...they are caused by related pattern frequencies in the subject, imaging device and output device.

There are several ways to avoid them.

1. Take care when shooting fine repeating rectangular patterns, moires often occur at one or several zoom/proximity levels..quite often you can eliminate the moire by adjusting the zoom, or moving the camera slightly.

2. Use a low-pass or diffusion filter to take the edge off of the fine detail. (this will help for moire that is happening in the camera (rare)

3. Lower the camera's vertical detail, and/or adjust the camera's sharpness setting downward (this will help with moire produced by the output device from an image that contains no moire (most common type of moire). This can also be accomplished in post.

Barry

Anthony Marotti · February 17th, 2005, 09:13 AM

<<<-- Originally posted by Marty Hudzik :
Anthony,
What images are you referring to? I am asking because you quoted me in your post but I have no idea what images you are talking about. -->>>

Hello,

Here is the quote that I should have quoted:

<<<-- Originally posted by Clive Collier : This isn't a joke I'm afraid.

Here are some shots to show clarity of image which is very impressive:

http://www.showreel.org/XL2/xl2stills.html

Will post morray pattern in a moment -->>>

Sorry about that !

February 17th, 2005, 09:13 AM	#154
Anthony Marotti Major Player Join Date: Feb 2005 Location: Rochester, NY Posts: 263	<<<-- Originally posted by Marty Hudzik : Anthony, What images are you referring to? I am asking because you quoted me in your post but I have no idea what images you are talking about. -->>> Hello, Here is the quote that I should have quoted: <<<-- Originally posted by Clive Collier : This isn't a joke I'm afraid. Here are some shots to show clarity of image which is very impressive: http://www.showreel.org/XL2/xl2stills.html Will post morray pattern in a moment -->>> Sorry about that ! __________________ AM

February 16th, 2005, 11:06 AM	#151
A. J. deLange Major Player Join Date: Jun 2004 Location: McLean, VA United States Posts: 749	I think it's been said dozens of times here and elsewhere but it is a difficult subject and people get confused so let me try to summarize. There is nothing wrong with the XL2 with respect to aliasing. Sampled systems are subject to aliasing which appears as moire in a two dimensional image unless the sampled information is strictly band limited to less than one half the sampling rate. Many cameras (especially still cameras) have optical antialiasing filters. The Canon video cameras apparently do not. Thus they are subject to moire but so are most other video cameras. Look at TV (including HD) and you will see moire. There is absolutely nothing that can be done about it except to reduce the spatial high frequency component of your image before it reaches the sensor. This can be done with blurring or diffusing filters. If you want to get rid of aliasing buy a blurring filter (and don't complain about the loss of resolution - you'll lose some). Once aliasing is in it is in forever - it cannot practically be removed though it is possible to mask it in post in some cases.

February 16th, 2005, 03:49 PM	#152
Per Oellgaard New Boot Join Date: Feb 2005 Location: Denmark Posts: 9	Thank`s Chris and A.J. I will try to do some shots in the comming weekend,, Denmark is when I´m off my job too Dark in the winterseason. I will let You know if Your adwise helps on the moire problem. A.J Thank You for a very concrete answer. I needed that during the discussion on this forum. I understand that moire is a normal thing. I watch the Olympics too. I see it every time I turn on my TV, even in a very expensive movie produced by the Danish Television (DR), and I accept moire as an intergraded part of making video, but I just think the ammount of moire is much too high with my brand new, in all other parts superlovely XL2. If it would be in anybodys interrest I have a shot as a very good evidence. I just don´t know how to link it to this page. Sorry to bring this up again.

February 16th, 2005, 05:13 PM	#153
Barry Goyette Trustee Join Date: Oct 2001 Location: San Luis Obispo CA Posts: 1,195	Per Just to reiterate one of my earlier posts on this subject... quite often the moire you are seeing is more relevant to the viewing device than it is the the camera. The originator of this thread was unable to show us the moire in the image itself because there was none. The higher resolution of the xl2's progressive mode will cause interlaced monitors to produce a moire even when one doesn't exist in the image itself. Such is the nature of moires...they are caused by related pattern frequencies in the subject, imaging device and output device. There are several ways to avoid them. 1. Take care when shooting fine repeating rectangular patterns, moires often occur at one or several zoom/proximity levels..quite often you can eliminate the moire by adjusting the zoom, or moving the camera slightly. 2. Use a low-pass or diffusion filter to take the edge off of the fine detail. (this will help for moire that is happening in the camera (rare) 3. Lower the camera's vertical detail, and/or adjust the camera's sharpness setting downward (this will help with moire produced by the output device from an image that contains no moire (most common type of moire). This can also be accomplished in post. Barry