Distorted grid effect in photo of LCD screen

[jreelawg]

What causes this effect? What am I seeing?

 

[I like Serena]

Hi jreelawg!

Are you referring to the http://en.wikipedia.org/wiki/Moir%C3%A9_pattern" ?

 

[berkeman]

Or possibly the refresh pattern. Can you post the picture that you are asking about, jreelawg?

 

[jreelawg]

Or possibly the refresh pattern. Can you post the picture that you are asking about, jreelawg?

This was a photo of my computer's LCD screen, of this symbol, with an all white background. I noticed the effect, and I made drastic adjustments to the contrast, sharpness, saturation, tint, temperature etc.

 

[jreelawg]

Here is what it looked like before adjusting the picture.

 

[I like Serena]

Yep. Moiré.

 

[sophiecentaur]

You get moiree patterns all over the place where there are two regular patterns of similar spatial frequency. I frequently risk driving off the road when going under foot bridges where the railings on either side produce a moiree pattern which seems to 'march' over the bridge. In imaging systems, the moiree is a result of sampling at too low a frequency, (spatial sub-sampling)which produces beat patterns. Every image sensor has a built in 'blurring' filter, to reduce the effect but it cannot be too savage or normal pictures would look too soft. You might notice that your effect goes away when you defocus slightly. (If your camera will allow it).

Wagon wheels going backwards in cowboy films are an example of temporal subsampling - same basic theory.

 

[russ_watters]

I'm seeing both a moire pattern and the actual grid of the LCD screen...you do know an LCD screen is a grid of multi-colored dots, right?