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12-01-2009, 04:40 PM   #1
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Kx (jpg) ISO Performance

I wanted to see how the Kx IQ varied with different ISO settings -
I realize it's only JPG - but that is what I shoot with mainly.

Scene -

the two areas shown are the 100% crops compared below -
I was trying to look at "shadow" and transition to highlight noise -
(basically I tried to pick the "shadow" area where I could see the most noise)










It appears that the Kx produces more than acceptable images at ISO3200 at least in terms of noise.

I thought the ISO6400 got somewhat ugly relatively speaking - so that's why I included a shot at ISO5000 - just to see if there any noticeable improvement. I think there just is.

But how has noise and noise reduction reduced definition?

Target at center of frame:


Took 100% crops from the top left corners of each panel -






ISO12800 looks pretty bad - but don't forget this at literally the pixel level and I've used a very demanding target.

ISO6400 is better - but I consider it still pretty ugly at 100% -
That's why I have a shot at ISO5000 (1/3 step down) and there is a just perceptible improvement.

I have wondered about shoot at 10Mp - if that would reduce the noise -
here are 10Mp shots at ISO5000 -




I think there is just a perceptible improvement -
but is there some loss in detail?


Last edited by UnknownVT; 12-01-2009 at 05:03 PM. Reason: pressed Post too early - added rest of crops
12-01-2009, 04:52 PM   #2
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Quite acceptable at least until ISO 3200.
Were these all shot to obtain the same exposures in camera? ie. in M mode with proportional changes in shutter speed to maintain the same exposure between shot with different sensitivities?
12-01-2009, 04:58 PM   #3
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QuoteOriginally posted by Ash Quote
Quite acceptable at least until ISO 3200.
Were these all shot to obtain the same exposures in camera? ie. in M mode with proportional changes in shutter speed to maintain the same exposure between shot with different sensitivities?
Yes, the EXIF information is still attached
although I used "P" mode to compensate the exposure for the change in sensitivity.

I pressed the Post button "prematurely" -
there are a lot more crops to show the loss in definition.
12-01-2009, 06:13 PM   #4
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Useful test. From where I'm sitting, there seems only a modest drop-off in definition up to 6400, especially considering these are JPG's. Depending on your print sizes it could be very usable even at 6400 pretty much straight out of camera. Do some careful de-noising of the JPG's and maybe a bit of USM etc and it will get even better.

I think we are getting spoilt by the K-x. We are now talking about usable resolution JPG output at 6400 ISO, and acceptable small print size/web use JPG's (like the first image) coming out of camera at 12800.

Who woulda thought...

12-01-2009, 06:25 PM   #5
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Just as an addendum to my previous post, your results correspond to the photoreview chart below that shows K-x lph resolution vs ISO only slowly degrading as ISO increases:



from
Pentax K-x, digital cameras, digital photography, photography, digital slr, camera recommendation, price comparison, photographic companies, camera companies, digital camera best prices,

where they say:
QuoteQuote:
Resolution remained relatively high throughout the test camera's sensitivity range with a surprisingly small difference revealed between the ISO 200 and ISO 12800 settings.
The chart also usefully shows the extra resolution advantage of working with RAW.
12-01-2009, 06:54 PM   #6
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QuoteOriginally posted by rawr Quote
The chart also usefully shows the extra resolution advantage of working with RAW.
Many thanks for your posts and comments.

Yes, indeed I realize that RAW would give better resolution results -
but I shoot a lot and have to process a lot - RAW would require an extra step and I really need to be able to do it as a batch - which in a way defeats the purpose of RAW if I can't give each shot individual development.

What I do find gratifying is how good those JPGs are -
shows that Pentax have really done well in extracting good IQ from that sensor.

A lot of my work is destined for the web which really means the results are about 600x400 pixels (cough-cough)
I hardly even need 3Mp much less 12Mp of the Kx -
and I probably can get away with ISO12800 for that size -
for example that first full-frame shot showing the positions of the crops is actually from the ISO12800 shot - at that size it looks pretty good to me.
12-01-2009, 07:18 PM   #7
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You are right - for day to day use and for simplified workflows, I agree that JPG sure does the job.

I usually save RAW+(DNG) so I have both formats at hand, just in case I need to squeeze an extra 10-20% extra resolution out of an image, or play with it in other serious ways. But most times I just use the out of camera K-x JPG's, and maybe just resize etc, and they are plenty fine.

PS: your example images may have been picking up a bit of extra noise due to the +2 Sharpness and +2 Contrast happening in your JPG's. Sometimes that accentuates visible noise. That's another parameter that may be tweaked for perhaps even cleaner JPG output.
12-01-2009, 07:33 PM   #8
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QuoteOriginally posted by rawr Quote
PS: your example images may have been picking up a bit of extra noise due to the +2 Sharpness and +2 Contrast happening in your JPG's. Sometimes that accentuates visible noise. That's another parameter that may be tweaked for perhaps even cleaner JPG output.
Actually I deliberately set the Kx up to the default "Bright" setting - which has those sharpness and contrast setting.

I started with "Natural" setting - because I have a K100D and that was much better than its default "Bright" setting which I felt was over-done.

However I felt the Kx "Natural" shots seemed somehow to lack punch - and went and set the sharpening up a notch (to zero) - but even then the results were still somewhat bland. So I tried "bright" and it was much better to my eyes - the Kx "Bright" is not as over blown as on the K100D and without the overtly yellow/warm cast - I actually like the Kx "Bright" setting over the "Natural".

The "Bright" setting has Sharpening at only one click above level or zero -
it's the same for Contrast

12-02-2009, 12:29 AM   #9
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Just thought I'd point out some of the improvements in the Kx over almost any other dSLRs.

The test shots were all shot with AWB (Auto White Balance) - while the lighting was a single CFL (Compact Fluorescent Light) of 2,700K - 10w (40 watt equivalent)

Up to now most AWB on dSLRs seem to be pretty poor when balancing tungsten lighting (about 2,700K) - the manufacturers say that they balance so that artificial tungsten lighting will look like artificial lighting - but most reviews criticize this approach. Most compact digitals seem to do a better job than any dSLR.

However as one can see this Pentax Kx did a really good job on AWB to get the color balance right - look at the whites on the central test chart.

Of course I have the custom setting of Strong correction for Tungsten lighting under AWB set - and I am very impressed with the results.

Pentax have very wisely still allowed for the weaker correction like most other dSLRs with the option of "subtle" correction for Tungsten lighting under AWB - and despite most reviews' negativity - I can see sometimes that kind of weaker/subtle correction may be better.

I also like the Control Panel and the ability to use the e-dial to switch the selected mode right there - so much so that I do not miss the top LCD.
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