Red noise

[GrahamH]

Hi all,
I'm using a Sony A77 and I find the noise in the darker areas seems to show up red.
Is this a known problem? When I was previously shooting with a Sony A350, I never saw this problem.
I'm intending to get back into portraiture and this could be a problem.
I processed the below image HDR (first attempt) but the red noise shows in many images and has done ever since I got the camera back February (one of the first after the flood issues).
I know if I expose for the shadows, it's not a problem, but not always possible.
Any feedback welcome. Technical issue internal to camera? General Sony issue?
Noise correction doesn't touch it.
I find it unsightly, acne ridden pictures.

Thanks.
Graham

[tclune]

Have you tried running a median filter on the red channel? It looks like that ought to work like a charm. FWIW.

[GrahamH]

Thanks Tom,
Sounds like one of the few applications CS can do. I work with PS Elements 10 and LR2.
If I desaturate the reds (masking as appropriate), I get the blotches turning grey and so are still visible.
So far I add a blending layer (soft light) and burn the areas. If the area is localised, no problem, but little bitty bits all over is not good.
Graham

[xpatUSA]

It seems that the dark areas are at the "noise floor" of the red pixels. If part of the HDR technique (with which I'm not familiar) is to amplify the shadows then that noise becomes more visible relative to the overall image. Nothing new said there, really. But the implication is that noise of that magnitude will be difficult to post-process out.

If the original was a JPEG, were there any in-camera settings (e.g. vivid?) that could have exacerbated the noise?

Did whoever serviced the camera install different i.e. later firmware? (long shot).

[John Morton]

My guess would be that these artifacts are primarily from the HDR process.

When the exposures in an HDR sequence offer the program used any option other than pitch black within an area of the overall image, the program tends to default to that option.

I would guess that these areas of your image are all but black in each exposure, and the HDR program is grabbing "red noise" from the darkest (noisiest) exposure and introducing it into the final image blend.

Try redoing the whole process exactly as you did before, but without including the darkest exposure in the image sequence and see if that makes any difference.

[kdoc856]

Hey, Graham

I'm also shooting with the Sony A77. Love the camera, and have been happy with everything except the noise in low light shooting (which I do alot,unfortunately). But this red noise is new to me, and I would think is an artifact of tone -mapping, although I have done HDR with both Photomatix and Nik HDR, and not seen it with either of those. That red noise is so bad that I thought those were berry bushes at first. Wish I could be of more help- will certainly follow this thread as anything to do with noise and the a77 has my attention.

Cheers,

Kevin

[GrahamH]

Hi all, thanks for your comments.
There is a saying I frequently use: -
A mistake is not a problem, merely an opportunity to learn.
Well, I have learnt.

As I indicated in my original post, the red noise is NOT due to the HDR. My fault I should have posted a non-HDR shot to eliminate such ambiguity.
I shoot RAW+JPEG and process the RAW file for the images of further interest.

As a result of your comments, it gave me a better direction to investigate.
It now seems that I am over processing the shadows in an attempt to pull out TOO much detail. The areas showing in the red/acne are the clipped/underexposed pixels. When I am pulling detail out of the non-clipped zones, it is also affecting the clipped zones and creating this acne effect.
So, it is NOT the camera, but my processing that is at fault.
I checked thee original RAW, original JPEG as well as the processed RAW and it was then evident what I had done.
As I get to understand the processing tools more, it seems that I have gone TOO far and am now abusing the tools.
Yes, I admit it, I am an abuser. I promise to try to change my ways - so contrite.

I am trying to get too much out of a single shot, I need to use the tripod more and bracket more.
The tools we use are so powerful, it's easy to forget that they have limits too. Seems I have found at least one of them.

Thanks all for your help.
Problem identified, possible solutions being investigated, in and out of camera.

Graham
Loves to learn.