CMCM
Veteran Member
Can someone explain to me why a camera having NO AA filter is a good thing. If I understand correctly, NOT having it can make for sharper photos. But if that's the case, why is it still there on certain cameras?
-
Welcome to the new forums! Please read this first. For known issues we are working to resolve, click here.
About AA filters
- Thread starter CMCM
- Start date
Leonard Migliore
Forum Pro
When you have fine structures in your subject, they can interact with the pixel spacing to produce false texture. This is called moire. It can be very annoying with fabric or many other repetitive surfaces. So cameras have AA (anti-aliasing) filters to make the image less sharp than the pixel spacing. This prevents the sensor from generating false textures.
But, by design, an AA filter makes the image less sharp. Cameras with very small pixel size don't need AA filters because the lenses can't resolve that much detail anyway. Cameras with bigger pixels often have AA filters to avoid moire at a small cost in sharpness.
OpticsEngineer
Veteran Member
"NOT having it can make for sharper photos. But if that's the case, why is it still there on certain cameras?"
The AA filter is intended to reduce Moire effects and aliasing. Where fine repetitive structures cause colored bands that are noticeable.
Most normal scenes like landscapes don't have those fine repetitive patterns. But some things do. The most common one I am aware of being expensive fabrics on things like wedding dresses that have fine textures. No bride wants to see colored bands running across their dress.
The colored bands have become less of a problem in recent years with higher resolution cameras and better signal processing algorithms. It can still be a problem though.
The AA filter is intended to reduce Moire effects and aliasing. Where fine repetitive structures cause colored bands that are noticeable.
Most normal scenes like landscapes don't have those fine repetitive patterns. But some things do. The most common one I am aware of being expensive fabrics on things like wedding dresses that have fine textures. No bride wants to see colored bands running across their dress.
The colored bands have become less of a problem in recent years with higher resolution cameras and better signal processing algorithms. It can still be a problem though.
Mark S Abeln
Forum Pro
Video and digital cinema still use antialias filters. They also use diffusion filters over the lens which blurs the image a bit and can help tame aliasing.
Noticeable aliasing is a disaster in motion pictures.
Noticeable aliasing is a disaster in motion pictures.
Mackiesback
Forum Pro
I was recently experiencing what I suspect might be moire related artifacts; only visible when it tried sizing down a photo (shot with the D500 that lacks the filter)... this is what happened (look at the teal fabric):
Moiré? D500
--
--------------------------------------------------------------------------------------------------------------------------------------
Knew very little about photography when I decided to buy the awesome Nikon D70; learned quickly that this expensive camera didn't make me a good photographer.
Moiré? D500
--
--------------------------------------------------------------------------------------------------------------------------------------
Knew very little about photography when I decided to buy the awesome Nikon D70; learned quickly that this expensive camera didn't make me a good photographer.
bobn2
Forum Pro
The anti-aliasing filter is there to stop aliasing. Aliasing is a phenomenon that occurs when there is captured detail finer than the pixel array can deal with. What happens is that this incomplete data can interact to produce patterns in the photo that aren't there in the real image. The most obvious one is 'Moire', which is bands or ring patterns in the image, and is particularly visible when it interacts with the colour filter array to produce coloured bands. However, 'Moire' is not the only form of aliasing, you also get 'jaggies', step in lines that should be smooth, and often subtle changes in texture, sand that looks like lawn, velvet that looks like grit, etc.
However, an aliased image can look subjectively sharper, and this has become a fashion to which some camera manufacturers pander.
I'm not sure if Pentax are alone in having AA filter simulation .
In their implementation , the camera has no AA filter in front of the sensor , but instead can use microscopic movement of the sensor , made possible by the anti-shake sensor movement facility , to achieve the same effect .
The beauty of this is that it can be turned on or off , and even implemented at different strengths .
Other makes will catch up ... eventually .
In their implementation , the camera has no AA filter in front of the sensor , but instead can use microscopic movement of the sensor , made possible by the anti-shake sensor movement facility , to achieve the same effect .
The beauty of this is that it can be turned on or off , and even implemented at different strengths .
Other makes will catch up ... eventually .
Mark S Abeln
Forum Pro
Downsizing digital images from any camera — with an AA filter or not — can also cause the moiré effect or aliasing.I was recently experiencing what I suspect might be moire related artifacts; only visible when it tried sizing down a photo (shot with the D500 that lacks the filter)... this is what happened (look at the teal fabric):
Moiré? D500
Also be aware that some objects naturally display a moiré pattern, and this has nothing whatsoever to do with digital artifacts:
The word moiré comes from a French fabric which exhibits this phenomenon.
You can get rid of digital moiré by adding some blurring to an image before you reduce its size. This will make your image appear a bit soft, and so you might want to add some sharpening after you resize it.
This old article describes what's going on with moiré and aliasing:
The Problem of Resizing Images
IMAGINE YOU HAVE a peculiar boss at work. He wants to make sure that you are at your desk working forty hours per week. So once a day (seve...
therefractedlight.blogspot.com
--
The Refracted Light
A website about the Art and Science of Photography
therefractedlight.blogspot.com
Mr Garibaldi
Leading Member
You are right (and I managed to fix it using the "median" filter in PS), with that said, after shooting several 10's of thousands of photos I have never experienced it before (using D70,D300 and D800) hence i wonder if not having an AA filter would increase the possibility of unwanted effects like this (when re-sizing).
--
--------------------------------------------------------------------------------------------------------------------------------------
Knew very little about photography when I decided to buy the awesome Nikon D70; learned quickly that this expensive camera didn't make me a good photographer.
Downsizing digital images from any camera — with an AA filter or not — can also cause the moiré effect or aliasing.I was recently experiencing what I suspect might be moire related artifacts; only visible when it tried sizing down a photo (shot with the D500 that lacks the filter)... this is what happened (look at the teal fabric):
Moiré? D500
Also be aware that some objects naturally display a moiré pattern, and this has nothing whatsoever to do with digital artifacts:
The word moiré comes from a French fabric which exhibits this phenomenon.
You can get rid of digital moiré by adding some blurring to an image before you reduce its size. This will make your image appear a bit soft, and so you might want to add some sharpening after you resize it.
This old article describes what's going on with moiré and aliasing:
http://therefractedlight.blogspot.com/2010/12/problem-of-resizing-images.html
--
http://therefractedlight.blogspot.com
--
--------------------------------------------------------------------------------------------------------------------------------------
Knew very little about photography when I decided to buy the awesome Nikon D70; learned quickly that this expensive camera didn't make me a good photographer.
Mark S Abeln
Forum Pro
Aliasing is still possible with the Pentax system (and one of the newer Micro 4/3rds cameras has it also?) but what it completely eliminates is color aliasing, which is a great benefit.
Basically, most cameras have different color filters at different pixel locations, and this offset can mean color artifacts even with purely monochrome subjects. A common fix for this is blurring the chroma, but you lose color detail, and it can be pretty obvious upon close inspection. The Pentax sensor shift system eliminates these color artifacts, but certainly you can still get moiré patterns and other aliasing.
A big problem with traditional antialias filters is that they aren't strong enough to eliminate color aliasing, and if they did, they would harm the resolution of the camera.
Mark S Abeln
Forum Pro
No, I would think that resizing would be the overwhelmingly main reason for aliasing when resizing significantly, whether or not the camera has an AA filter.
One partial solution to the problem is to use a better resizing algorithm. Lanczos resizing handles this better than the common bicubic or bilinear methods used in software.
Mark Scott Abeln - I think you're talking about different features.
There's the pixel shift mode that samples the scene four times with a 1px shift between each shot, meaning each output pixel has its own R, G and B information (and hence no colour moire).
There's a separate, single-shot mode called 'AA Filter Simulation' that vibrates the sensor by something like 1/2 a pixel width during the exposure to create the same magnitude of blur as a physical AA filter would.
Richard - dpreview.com
Last edited:
bobn2
Forum Pro
Indeed it might, although the Nikon D800E and Canon 5DsR suggest that some are willing to pay more for less.
--
Tinkety tonk old fruit, & down with the Nazis!
Bob
Last edited:
Mark S Abeln
Forum Pro
I'd completely forgotten about that feature!
John Sheehy
Forum Pro
I think he was talking about the sensor vibration to emulate an AA filter; not 4-exposure pixel shift.
The current type of optical AA filter couldn't be used to anti-alias the red and blue channels, because the 4 points of light would be spread so far apart for the red and blue channels that they would actually separate into 4 points in the green channel, with darker pixels between them.
I find it very ironic that the current AA filters used in CFA cameras are actually perfect for a monochrome or pre-Quattro Foveon sensor, but those sensors don't use AA filters.
Similar threads
Keyboard shortcuts
- f
- Forum