Strange noise in JPEG

JPG pictures taken with my brand new PowerShot G2 have a strange pattern of light and dark pixels. Noise can be observed easily in the dark and midtone areas, of the image at:
http://www.pbase.com/a​m354/jpeg_noise

Viewing the image at original size you will see it as a noise. To see the pattern better download the image and look at high magnifications (i.e. 600%).
The noise is visible only for shots saved as JPG (I tried fine and superfine). Shots saved as RAW are fine.

Any clue about what is going on? Am I doing something bad? Or is just bad luck and I will have to send the camera for repair?

Thanks,

Adrian

I don't see anything in the image that is not typical JPEG compression artifacts. JPEG isn't magic; you get an incredible reduction in file size with it, but there is a price.

To make sure we talk about the same thing I added an image with a detail of the bottom left 49x35 pixels of the pumpkin image. For easy viewing each pixel from the original image is magnified to a 5x5 pixel square. The pattern of bright and dark pixels is evident.

I don't think they are JPEG artifacts:
a. I did comparative shots of the same subject and saved in JPEG and RAW. The RAW image was converted to TIFF and JPEG compressed to a similar sized file with Photoshop. The pattern wasn't there.
b. I also looked at shots taken by a friend with another G2, JPEG compression and no post processing - the pattern isn't there.
c. I looked on the web for images with examples of JPEG artifacts. They look different.

What makes you think these are JPEG artifacts? Do you get the same pattern when you save your pictures in JPEG? What digital camera do you use?

No.. Those aren't typical JPEG artifacts at all.
What ISO is your camera set to? It doesn't look like typical high ISO noise either, but I can't think of anything else.

Jason.

The full size image looks like it has a layer of dust on it. Very odd. If the outside of the lens is not obviously dirty, and if as you say you only see the "noise" with JPEGs and not RAW images, you should contact Canon for service work under your warranty.

Best of luck,

Jason,

ISO was set to 50. It has its place in the exif record but it looks like the G2 doesn't set it.

Slejhamer,

Yes it looks like dust but it is not. The lens is clean. Any dust on lens will show only like a soft image. Dust on the CCD will show up sharp, black and will show on RAW also. So it is not dust on CCD.

I suspect a problem with JPEG compression. As it doesn't show up in other G2s I think they do JPEG compression in hardware and that particular circuit has problems in my camera.

Adrian

If you're seeing non-JPEG type noise in JPEG images and not RAW, then I think you're right. It may well be a hardware problem.

Hi, I have seen the same noise too, both in night shots and midtone and dark areas of late-afternoon shots, even with ISO50. Have you contact Canon? What's your final findings on this problem? I appreciate any information.

I would get that camera back to Canon right away. Mine is a year and a half old, but I have updated the firmware a couple of times. It never shows the "pepper" all over the photo like I see on the pumpkin photo.

For the record, I used to shoot only JPEG (minimum compression and the largest format), and now shoot mostly RAW. I always use ISO50. Never has anything like that showed up.

I agree with your analysis of CCD and lens cleanliness. This is not dust. Dust on the CCD wouldn't cover individual pixels, anyhow. The pixel space on the CCD is too small for dust to cover only one at a time.

I hate to say it but it looks like CCD noise to me. Not gain or ISO but the type of noise you get from a long exposure where some pixels on the CCD are hotter than others.

Try this, Take a 1 second explosure with the lens covered so no light enters the camera. Then look at the resulting picture and look for pixels that stand out. If you see hot pixels doing this test then your CCD may be sub-standard and my require replacement. 1 second should be long enough to visibly see any hot pixels, but short enough that the camera's noise reduction doesn't kick in. You should only be seeing hot pixels with very long exposures, not normal shutter speeds.