Question about Pentax *ist D Digital Camera

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*ist RAW converter problem

I just discovered a peculiar thing about the RAW converter. It seems to add grain not normally visible on in-camera jpegs. Please have a look at the sample below. It's the same image (300% crop), taken in RAW mode. 1st pic converted with photoLab to jpg (default settings) 2nd pic converted with photoLab to tif 3rd pic is a screen grab of display within photolab (before converting). Notice that both 1st & 3rd pic have the characteristic 2:1 jpeg downsampling problems (eg. around bart's red collar). The TIFF naturally is ok, as the colour info is not reduced. But both 1st & 2nd pic show a lot of grain (noise?) which is not visible in the 3rd. From my experiments, in-camera jpegs also do not show that grain. Is this a photoLab problem? or is in-camera processing smoothing the problem out? Does anyone have similar experiences? (also, why can't digital cameras save JPEGS in the maximum 4:4:4 format, where colour info is not sub-sampled??)

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Re: *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.

Posted on Sep 08, 2005

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Re: *ist RAW converter problem

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...

Posted on Sep 08, 2005

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Re: *ist RAW converter problem

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.

Posted on Sep 08, 2005

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