Wednesday, April 25, 2007

(Unique) Colour Moire Problem of the K10D

As you may know, Klaus Schroiff of PhotoZone is now testing the K10D, also along with some of the more common Pentax lenses.

Whilst his full review on the K10D hasn't yet been published, nor any of his Pentax lens tests, all of which I believe are still under progress, his latest findings have revealed that the K10D does produce a special type of colour moire artifacts which is unique amongst all of the 10Mega-Pixel DSLRs which use the Sony 10MP APS-C CCDs:-

As we can see from the test shots of the resolution test charts at 100%, those colour moires are particularly visible, for images converted with ACR 3.7 and Raw Therapee V2. With Pentax's original Photo Laboratory 3.1 (PPL 3.1), it seems that the software tries to eliminate something, but then the image's contrast and sharpness are reduced dramatically with obvious blur and resolution is greatly affected.

Following down the PhotoZone discussion thread of the above, the same test shot made with the Sony A100 can be compared and it is clear that the Sony one does not exhibit similar problems.

Well, it is guessed and generally agreed that the possible cause for this problem is that a very weak Anti-Aliasing (AA) filter has been chosen and used by Pentax. However, Pentax has failed to manage the aliasing problem, no matter for the hardware and firmware/software used in the K10D, without scarifying resolution and image quality.

The good thing is that it is the first time I can see some very simple but solid evidence and a very sensible answer to the K10D image low fidelity problem for its in-camera jpegs and why also for converted RAWs with original PPL 3.1, which this problem have never been found with the K100D. So, it is probably a hardware problem inside the K10D for some limitations and barriers which Pentax has not yet able to break through at this moment. Indeed, the comparatively lower image quality of the K10D was first suggested by Phil Askey but then he hasn't commented any further on the possible cause(s) to the problems he found in his review, nor Phil Askey mentioned anything about the problem of colour moires, which is for the first time pointed out by Klaus. In fact, as Klaus has pointed out in the above thread that same symptoms do indeed show up in the sample image of the of the DC Resource Samsung GX-10 review.

Nonetheless, besides, from what I can see from the thread and another previous thread mentioned for what Klaus has tested and found, actually Imatest is not really something very reliable in determining the resolution figure of LW/PH (Line Widths per Picture Height) by the method of calculating the highest spatial frequency by plotting the Spatial Frequency Response (SPR) curve via some mathematical methods and algorithms (simple Fourier transform?), which is also very susceptible to image noise and other artifacts, say, colour moires. So, sometimes a higher Imatest LW/PH figure does *not* really mean a higher resolution nor a better image (with good quality) afterall.

Read also:- The Secrets of the K10D (Part 1 of 3): The Heart - The CCD Imager

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