Nasty moire on my wall

[gerolamo]

Or at least i think it's moire.
So this is the story:

Finally I got my 20Dand is awesome. i played with it for a few days, using JPG because I had a small CF card. Great quality, fast, etc.
So this nigth I get my 1G card, put it in, start playing with raw - first thing I shoot is the painting on my wall - and it looks like this.

The wall is completely white, but this is what I get using the normal room lighting at ISO 3200. (You can see the light source in the picture, and it causes the same effect on all the walls, all light balances, all distances etc). The jpg copy is fine.

The effect dims when using flash and dissapears if I turn off the light. I get the same effect if I use a different lamp.

http://www.geocities.com/mihai_cs/moire.jpg

Any ideas what is going on? I hope it's not the camera, but I would like to know if this is normal for a dSLR. I've had SLR's since I was 10, and I also have a P&S digital, so I like to think I'm not exactly a newbie, but this really was an unpleasant surprise.

Camera Model
Canon EOS 20D
Shooting Date/Time
15/10/2004 12:42:21 PM
Shooting Mode
Shutter-Priority AE
Tv( Shutter Speed )
1/100
Av( Aperture Value )
7.1
Metering Mode
Evaluative Metering
Exposure Compensation
0
ISO Speed
3200
Lens
28.0 - 135.0 mm
Focal Length
28.0 mm
Image Size
3504x2336
Image Quality
RAW
Flash
Off
White Balance Mode
Auto
AF Mode
One-Shot AF
Parameters Settings
Contrast Standard
Sharpness Standard
Color saturation Standard
Color tone 0
Color Space
sRGB
Noise Reduction
Off

[Chazs]

Far be it from me to know the problem, but my first guess is the lens coating and light interaction of some sort. I wonder if it would happen with a Skylight filter or UV Haze filter. But I do agree, it's a little disturbing.

[gerolamo]

I think my wall hates my camera.

http://www.geocities.com/mihai_cs/moire2.jpg

Actually the wall is not completely smooth, it has a grainy finish, even though it is painted white. I wonder if it has anything to do with this.

[Cal Maier]

Your White Balance is off. I noticed that you've got the camera set to Auto White Balance, and the room light is obviously closer to the colour temp. of Tungsten lighting. This is why, you do not get the gold/brown colour when you turn out the room light, or it's not as prominent when the flash is used. Also, at ISO 3200 I would expect to get similar halos and other artifacts when pointing the camera almost directly at the light source.

You shot the first file in RAW, so why don't you just change the WB to Tungsten or choose around 3000 degrees Kelvin, and that should make a difference in the colour of the wall. If you need to shoot into the light source you can minimize the lens flare (halo effect) by trying a proper lens shade for your lens.

Try shooting at ISO 400 and use a tripod and custom WB and you should get much better results.

Cal CPS432

[gerolamo]

Awsome Cal, thanks a bunch.
I set the balance to 3000, reduced the ISO and the moire is gone. It still doesn't like ISO 3200 though, I'll have to test it a bit more.





Once a newbie, always a newbie.





[/quote]

[drisley]

Excellent work Cal!
I was going to say his house was haunted, but I think your idea might be better. :D

[maderito]

I set the balance to 3000, reduced the ISO and the moire is gone. It still doesn't like ISO 3200 though, I'll have to test it a bit more.

Aisde from the WB issue, there still remains the moire/banding phenomenon nicely illustrated in these photos. It seems clear that it is related to ISO 3200. It is likely a digital signal acquisition and/or processing artifact. I agree with Drisley - it looks spooky. :shock:

My question would be: Is this artifact generated during in-camera processing or post processing?

Although the EXIF data shows that in camera "noise suppression" is turned off, that only applies to long exposures (=> 1 sec). There are other noise supression and anti-aliasing processing steps that occur before the image is delivered up in its RAW format. In post processing, different software programs further add to or reduce this problem by applying their own noise and moire/banding reduction techniques when converting RAW to JPEG or TIFF.

What RAW conversion software was used? What software settings, if any, where applied for noise, moire, or banding reduction? (Some of these are set as "defaults.")

[gerolamo]

I am using the software that came with the camera. What is weird is that the jpg copy made during the shoot looks fine, but the embeded jpg shows the bands.
I can see it when I preview the file with the EOS viewer program. And it appears with any settings I use to convert to tiff.

I tested it again this mornig - with side lighting - from the window this time - and I get the same effect if I use the wrong balance.

Works fine with AWB though, for ISO 3200.