[Philoslothical]

Not if exposure compensation was involved

Very true, good point. It doesn't seem to apply here unless his EXIF data is incorrect somehow, but the possibility should have occurred to me.

[rawr]

Windows photo viewer

There's your possible culprit. Run a mile away from Windows Photo Viewer. Only yesterday I saw a user on another forum complaining about how it mangles his JPEGs.

Download something respectable like Fastone Image Viewer (it's freeware) for your basic image manipulations, cropping and resizing. Even Picasa will do better than Windows Photo Viewer.

Other than that your basic EXIF shows pretty normal settings except an unusually high shutter speed for the scene you describe. Given that you seem to have been using centre-weighted AE, and you say the light source was way out of frame, and it doesn't appear exposure compensation has been used, the other things that may account for the high shutterspeed may be stuff like light entering the viewfinder, or AE-L being left on from the camera metering a brighter previous scene.

Either way all this is just guesswork without seeing the full un-cropped image with full EXIF. But hopefully it may be helpful.

[Chex]

1/1600s @ f5.6 in most daytime situations would be underexposing.. unless shooting "action" shots, I never shoot over 1/320s.. without EXIF Data no idea what mode you were shooting in.. but I would suggest shooting in M or Tv mode and not letting your shutter speeds get out of hand, shooting in M will definitely make you blow a few shots.. but will also train you to check your exposure settings. Even shooting in Tv mode and keeping your shutter speeds around 1/250-320s and letting the camera deal with the rest could eleviate shots underexposing to this degree. But every shot is different I guess!

[twitch]

I'd like to see the whole picture... in aperture priority it's possible to get that sort of shutter speed on a K-x if the ISO was set as fixed at 400 and the scene near the centre of the pic was very very bright and/or some negative EV comp was set.

All it needs then is some pushing of exposure in PP by some software in the chain to get that degree of noise.

I'm not yet ruling out that the camera did the right thing ....

[rawr]

some software in the chain to get that degree of noise.

Indeed. One of the complaints about Windows Photo Viewer I have come across is that it can produce horrible posterization in JPEGs it modifies.

If you look at the noise in the original image of the OP's, it's not the normal very fine-grained K-x noise we all know and love, but big blocky lumps of shadow noise - especially visible on the dudes forearms. Something else other than the in-camera JPEG engine has certainly produced that mess. This is happening alongside the general under-exposure, so we are seeing a double-dose of problems here.

[photoleet]

There's your possible culprit. Run a mile away from Windows Photo Viewer. Only yesterday I saw a user on another forum complaining about how it mangles his JPEGs.

Download something respectable like Fastone Image Viewer (it's freeware) for your basic image manipulations, cropping and resizing. Even Picasa will do better than Windows Photo Viewer.

Other than that your basic EXIF shows pretty normal settings except an unusually high shutter speed for the scene you describe. Given that you seem to have been using centre-weighted AE, and you say the light source was way out of frame, and it doesn't appear exposure compensation has been used, the other things that may account for the high shutterspeed may be stuff like light entering the viewfinder, or AE-L being left on from the camera metering a brighter previous scene.

Either way all this is just guesswork without seeing the full un-cropped image with full EXIF. But hopefully it may be helpful.

I have Faststone, but on this occasion just used the Windows picture viewer to rotate the image. I'll take some shots next times indoors and see if I can reproduce this effect.

Here is another shot that had similar effect

First is the complete shot with just the faces blacked out, no other settings changed. Next is the 100% crop of the noise area. Click on the images for 100% view





Here's the EXIF of the image

Code:

Result
File size : 907276 Bytes
MIME type : image/jpeg
Image size : 1776 x 1086
Camera make : PENTAX
Camera model : PENTAX K-x
Image timestamp : 2011:09:18 14:35:52
Image number :
Exposure time : 1/400 s
Aperture : F7.1
Exposure bias : 0
Flash : No, compulsory
Flash bias :
Focal length : 18.0 mm (35 mm equivalent: 27.0 mm)
Subject distance:
ISO speed : 500
Exposure mode : Aperture priority
Metering mode : Multi-segment
Macro mode :
Image quality :
Exif Resolution : 1776 x 1086
White balance : Auto
Thumbnail : None
Copyright : PHOTOLEET
Exif comment :

[rawr]

With these the exposure seems OK, but the problem is the lumpy looking noise.

To eliminate the in-camera JPG processing as an issue, do these things:

- set the JPEG quality in the camera to the maximum 12MP and 3-Stars;
- set the Custom Image settings to Natural,
- turn off or set to Low all in-camera NR, and
- set the start level for NR to something high like 3200 ISO.

Then set the camera to record RAW + JPEG, and shoot some scenes with dark areas. Then use Pentax Digital Camera Utility 4 to produce JPEGs from the RAWs without applying any NR, and compare them with the JPEG's out of camera, looking carefully to see how shadow areas are rendered.

And don't let Windows Photo Viewer anywhere near your images.

[photoleet]

With these the exposure seems OK, but the problem is the lumpy looking noise.

To eliminate the in-camera JPG processing as an issue, do these things:

- set the JPEG quality in the camera to the maximum 12MP and 3-Stars;
- set the Custom Image settings to Natural,
- turn off or set to Low all in-camera NR, and
- set the start level for NR to something high like 3200 ISO.

Then set the camera to record RAW + JPEG, and shoot some scenes with dark areas. Then use Pentax Digital Camera Utility 4 to produce JPEGs from the RAWs without applying any NR, and compare them with the JPEG's out of camera, looking carefully to see how shadow areas are rendered.

And don't let Windows Photo Viewer anywhere near your images.

Cool, I'll try this.

What about highlight and shadow correction ?

[rawr]

What about highlight and shadow correction ?

Turn them off too. May as well just go completely vanilla with the in-camera JPG's while you debug this. You can always easily add highlight/shadow correction when processing your RAW's anyhow, especially when using DCU 4.

And in practice I've found the benefits of either to be subtle to the point of almost not being visible. All I ever use for the in-camera JPG's is Shadow Correction - Low.

Best of luck!