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OLPF and MVC's


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#1 Cesar Rubio

Cesar Rubio
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  • Mexico/Wisconsin

Posted 20 October 2011 - 11:44 AM

Most engineers in the Machine Vision Cameras (MVC's) Industry don't even know what is an OLPF! (Optical Low Pass Filter)

MVC's are designed to resolve the most resolution the Bayer sensor is capable of, while regular video and digital photography cameras use an OLPF to “soften” the image a little bit (especially useful for people photography).

That is nothing new, “old film” portrait photographers used “soft” lenses, and even filters for the same purpose.

Most MVC's have an IR (Infra Red) Cut out filter as standard, which is useful for our purposes while recording snow scenes in 3-D (so I've heard)...

Also such filter serves as a “seal” for the inside camera components (including the sensor), so while changing lenses your sensor will never get dust! Great.

There are some aftermarket OLPF that are being used now mostly for DSLR's while recording video, to minimize the aliasing and moire problems.

But I don't think that they are the best answer to the problem, in order to work the best (minimize aliasing and moire while retaining the most resolution) OLPF have to be implemented in top of the sensor...so all aftermarket solutions will be sub-par at best.

What I do to minimize aliasing and moire with bayer sensors in MVC's, is what I learned 22 years ago when I started in professional portrait photography....I use “soft” lenses, that believe it or not serves as a “natural” OLPF!

Then in post I re-size or “down-convert” the footage by a 1.5 factor, and voila most (if not all) the aliasing and moire is gone, while retaining the sharpest image possible!

1080p to 720p will give you the best image quality. (1920x1080 pxs. to 1280x720 pxs.)

That's what most working with the Alexa Raw footage do as well, they start with 2880x1620 pxs. and re-size to 1920x1080 pxs in post.

That 1.5 factor works great for Bayer sensor cameras.

Although there are 5 MP and even 10 MP resolution lenses in the 2/3” c-mount lenses industry, usually I prefer the lenses that are rated as “Mega-Pixel” like these here: (and are cheaper as well)

http://www.machinevi...p=9&pageSize=10


Cesar Rubio
Wisconsin & LA.
http://dna-rubio-3d.blogspot.com/
http://dnarubio3d.wordpress.com/
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