*ist RAW converter problem

I suspect that it comes from an embedded image, as I mentioned in the other thread. This isn't surprising, as other Raw image formats do this, too. I notice that the sharpening settings aren't very sophisticated in the Pentax Raw Convertor (what a surprise!). I would try turning it entirely off or to its lowest level and post process the images with a good USM in another application so you can adjust sharpening radius and noise threshold. I think you'll find this will make a bit difference in keeping a low noise level in your images.

The image was taken at ISO200 (with flash), all the settings were left as default (ie at "0") during conversion. It would appear to me that the "photoLab onscreen display" uses the same algorithm as the camera (or maybe the entire in-camera jpeg is embeded within the RAW file?) Its curious, that PLab opens & displays the PEF file almost instantly, and yet it takes quite a long time to convert to a JPEG... If a full size jpeg was embeded, it would explain why the PEF is so oversized, and can sometimes vary in size by quite a large amount...

Ignoring the JPEG artifacts, which isn't about the extra grain in both the TIFF and JPEG images produced by the convertor, is it possible that different sharpness settings were used for the output images that for the on screen review? High values of sharpening without using an appropriate noise threshold value will have the effect of increasing noise/grain.