Moire Pattern
There is a type of color distortion present in digital cameras that can under certain circumstances be mistaken for chromatic aberration but it manifests itself differently. It is what is known as a Moire pattern.
Moire pattern first presented itself in color television as a result of overlap of sideband information in the NTSC color broadcasting system. In that system, color information overlaps high frequency (fine detail) video information and so fine repeating details, such as a plaid shirt or pen striped suit, would result in a rainbow effect.
Digital cameras also are subject to Moire pattern but for a different reason. In digital cameras, the pixels each respond to a specific color, red, green, or blue. The geometric pattern that they are laid out in can result in banding when a high contrast line cuts the pattern.
In the following example, the fence top rail wasn't quite horizontal in the original photo and was made horizontal with the straighten tool. Because it was originally at an angle, it cut the pattern of pixels at a slight angle and acquired this rainbow banding as a result.
It should be noted that this is a small portion of a much larger picture and without being blown up and having the color exaggerated it probably would have gone unnoticed.
The strongly predictable nature of the Moire pattern from a digital camera makes it very amiable to software removal. The internal firmware of many cameras do this well enough that you may never notice this, but if you do, know that you can fix it using external software.
In this case, I used Paintshop Pro X's Adjustments->Add/Remove Noise->Moire Pattern removal. While I was at it, I also adjusted the brightness curve because the original looked kind of dark and dreary to me, that's a matter of personal taste or in my case, lack thereof. The important thing to notice is the banding is gone.
Moire pattern first presented itself in color television as a result of overlap of sideband information in the NTSC color broadcasting system. In that system, color information overlaps high frequency (fine detail) video information and so fine repeating details, such as a plaid shirt or pen striped suit, would result in a rainbow effect.
Digital cameras also are subject to Moire pattern but for a different reason. In digital cameras, the pixels each respond to a specific color, red, green, or blue. The geometric pattern that they are laid out in can result in banding when a high contrast line cuts the pattern.
In the following example, the fence top rail wasn't quite horizontal in the original photo and was made horizontal with the straighten tool. Because it was originally at an angle, it cut the pattern of pixels at a slight angle and acquired this rainbow banding as a result.
It should be noted that this is a small portion of a much larger picture and without being blown up and having the color exaggerated it probably would have gone unnoticed.
The strongly predictable nature of the Moire pattern from a digital camera makes it very amiable to software removal. The internal firmware of many cameras do this well enough that you may never notice this, but if you do, know that you can fix it using external software.
In this case, I used Paintshop Pro X's Adjustments->Add/Remove Noise->Moire Pattern removal. While I was at it, I also adjusted the brightness curve because the original looked kind of dark and dreary to me, that's a matter of personal taste or in my case, lack thereof. The important thing to notice is the banding is gone.
posted by Nanook at 11:33 AM
2 Comments:
I have a Nikon D40 which I use to take pictures of houses for my wife's real estate business. I find moire all the time especially with the roofs. But when I enlarge the photo on Adobe Photoshop, it's gone. I have found that moire will not show up on prints either. I could be wrong about the prints, but have never had it to happen.
Moire patterns in an image result from the way an edge lines up with the color dots on the cameras sensor.
They can also result from the way an edge lines up with the color dots on a display, particularly a low resolution display with a large dot pitch. That is what you are seeing.
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