Production K-7 Dynamic Range vs. K20D...

Started Jul 10, 2009 | Discussions
GordonBGood Veteran Member • Posts: 6,311
Production K-7 Dynamic Range vs. K20D...

Yesterday I went to TheCameraStore in Calgary where I am vacationing and got to handle a production version K-7 as well as take away some test shots on my SD card. As far as handling and feature set compared to my K200D - WOW - everything one could possibly look at is times two, except for the price which is times three ;- . There is only one item that is not times two, and in fact is pretty much the same as my K200D or the K20D and that is Dynamic Range (DR), and this may have even gotten a little worse. My approach in determining this was as follows:

1) Although I shot two images each of 7 stop underexposed and normal exposures of a gray card (supplied by the store) at all ISO's from 100 to 6400 in DNG raw mode, I ended up basing my conclusions on mostly just the black areas of the sensor that are masked to light that the processing uses to determine the black level compensation. These images were shot with all High ISO Noise Reduction turned off in the Custom Menu and Extended Dynamic Range was not used.

2) I used my conversion software to output a Colour Filter Array (CFA) map and looked at the standard deviation of the green photosites in this black unexposed area. The standard "bell curve" has of course been clipped to zero at about the median, but I determined the standard deviation by using the fact that about 84& of the readings will be below the higher inflection point.

3) These standard deviations were compared to those found by the same method for similar K20D images.

Given that DR is limited by the noise "floor" at the black end of the response (as per the DxOMark definition), the low ISO DR for the production K-7 is about the same as that of the K20D, and the same as that of the beta K-7 images I analysed a month or two ago. The higher ISO DR for the K-7 is in fact worse than that of the K20D but that may be due to a different start point for the Noise Reduction (NR) that is applied. I think that any perceived improvement in high ISO image quality will be only due to possibly improve NR techniques, but these will likely also tend to smear details, reduce resolution, and make the noise "grain" to be coarser.

So I am somewhat disappointed that the K-7's image quality in this one respect is not up to the standards of the rest of the camera and that I will have to wait at least another camera generation in order to see Pentax work on competitive image quality as to DR.

Now I will qualify this that those who were happy with the K20D as to image quality will likely also be happy with the image quality from the K-7, and those who are willing to use NR on their images in order to obtain reasonable results at higher ISO's such as ISO 1600 (or even ISO 800) and up may be reasonably satisfied although definitely not ecstatic.

A high DR specification is of use to people who want a wide exposure latitude or the ability to underexpose their images and recover them by EV boosting in post processing to a good image quality standard without NR, and also the ability to compress the DR by boosting the brightness of the deep shadows to reveal shadow detail without noticeable noise artifacts. Those who only make use of the top 7 or 8 stops of DR with well exposure bright images will never notice its lack. However, there have been many who have found even the lower ISO's of the K20D to be somewhat noisier than the competitition and therefore somewhat limiting. In this respect, the K-7 is no better, and may even be somewhat worse at the higher ISO's.

I did not want to believe these results and checked them using the raw DNG K-7 files from a production camera posted on Imaging Resource. The results were essentially the same. So unless you want to believe that two random samples in Calgary, Canada and another in Atlanta GA both have the same characteristics that are contrary to the norm, it looks like this is real.

To those that pooh-pooh technical results without images, I assure you that you will see more noise in push processed deep shadows for the K-7 samples than in equivalent push processed other cameras with a wide DR such as the newer Nikon CMOS sensors at say ISO 200 (since Nikon doesn't have a true ISO 100). For now I'll leave that exercise for the student. Note that you will have to look into the very darkest part of the images for this test with about a +4 EV exposure boost such that the dark part of the images are less then about 64/255 JPEG levels and preferably about 32/255 JPEG levels even after the 4 EV boost in the raw conversion.

It is much more difficult to compare high ISO images due to the variances in Bayer processing and Noise Reduction techniques.

Regards, GordonBGood

Bart Hickman Veteran Member • Posts: 7,256
Re: Production K-7 Dynamic Range vs. K20D...

Hi Gordon,

Oh well. I guess if I had to pick something for them to improve between AF or sensor noise, I'd pick AF just because I lose more shots to that than I do to noise--even in low light situations requiring F/2.8 and ISO3200. So from that perspective, I suppose they did the right thing on the K7. Still, it'd be nice to get the extra DR. Sensor revisions must cost a fortune--I'd figure at least a $1 million.

I'm curious--do you think the limitation is still due to a preamplifier in front of the ADC?

Bart
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ManuH
ManuH Veteran Member • Posts: 3,898
Re: Production K-7 Dynamic Range vs. K20D...

Thanks Gordon for this information. I'm not surprised after looking at the first pictures I took with my K-7. It's not any better than the K20D, actually I even have the impression it's slightly noisier although I'll to do direct comparisons to make my mind about this. Fortunately almost everything else on the camera is great. But for IQ it is slightly disapointing given the known weaknesses of the K20D sensor and the time they had to improve on it.

solarider Veteran Member • Posts: 4,847
Re: Production K-7 Dynamic Range vs. K20D...

Gordon,

In your estimation, is this problem due to hardware or firmware or a combination... does a firware fix have any chance of improving the picture? pun not necessarily need to be intended ];-)

Thanks for this info. Glad to see it doesn't affect shooting in general.

Nic

jamesm007 Veteran Member • Posts: 5,663
Re: Production K-7 Dynamic Range vs. K20D...

Thanks again for the testing and writing your results. Well to be honest the only word I can think of that comes to mind in how I feel about the results is disappointed. Samsung/Pentax/Hoya claimed improved noise and that the shadow noise would be improved (PopularPhoto K-7 preview, July 2009).

Samsung rebuilt the sensor from the ground up and the engineers could not find even a 5% improvement in dark read noise.

Well in one repect the K20D is a fantastic sensor, and I can and do get although with some PP NR work - very nice ISO3200 pics no problem.

Be interesting what the pro-reviews say.

I do realize high ISO noise is not the most important thing in the world; that the the K-7 is still great through out its ISO range, and a fantastic Pentax dSLR offering the body/package and more of a top of the line FF from C/N in a smaller APS size.
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MightyMike Forum Pro • Posts: 40,646
Re: Production K-7 Dynamic Range vs. K20D...

Thanks Gordon, i liked my K20D and even though i haven't pixel peeped my K-7 yet i will like them too... there are those times where i need to push process, did it a lot more in the P&S days, not as necessary on the DSLRs i've owned however like i said there are those times... and yes i've noticed more noise but in most cases its not too much and it can be removed with a quick neat image without losing significant detail... however with the K20D i exposed to the right almost exclusively with EDR on which likely negated the need to push the shadows much at all, the highlights rarely clipped and the shadows got a longer shutter speed then lest say a regular exposure... it caused me to have longer shutter speeds but it was a compromise i was willing to make... chances are i won't have to expose as brightly on the K-7 dues to improved metering. i like your analysis but in the real world it doesn't make a lot of difference unless you regularly shoot critical scenes with high DR requirements
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viking79
viking79 Forum Pro • Posts: 14,156
Re: Production K-7 Dynamic Range vs. K20D...

Thanks for the analysis GordonBGood, I was looking forward to what you had to say, even if it wasn't what I wanted to hear. At the same time this is by far my favorite Pentax camera. It is worth every penny due to the other improvements. I think I prefer the high ISO noise of this camera to the K20d even if there is more noise. I am curious to what DxOMark finds with it too. So, does it bother me it isn't better? Not really, but I was hoping for 1/3rd stop improvement. Oh well.

Eric

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moving_comfort
moving_comfort Veteran Member • Posts: 8,242
Re: Production K-7 Dynamic Range vs. K20D...

jamesm007 wrote:

Samsung rebuilt the sensor from the ground up and the engineers could not find even a 5% improvement in dark read noise.

I keep seeing this repeated in various ways, and it's not really true - it's basically the same sensor core with reworked sensor peripherals (to vastly simplify it.)

Not "rebuilt from the ground up," although that would have been nice... You can only do so much about noise working with basically the same sensor.

.

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dotnik Veteran Member • Posts: 5,565
Re: Production K-7 Dynamic Range vs. K20D...

Thank you, Gordon.

Comparing high ISO images between the K20D and the K-7 I have noticed that the noise in the K-7 images tend to appear more dense in way and so I am not surprised that your calculations show more noise by numbers.

To me it looks like Pentax decided to control chroma noise as much as possible even at the cost of more luminous noise but I like the end effect it has on the K-7 images as colors tend to be deeper and slightly more consistant between low ISO and high ISO.

As a side effect my own conversions have shown that this approach have made it easier for the NR software to handle the noise and then I end up with a more appealing result but most importantly a more consistent result. That means apart from NR the same post processing can be applied to images regardless of being low ISO or high ISO making that part of process easier to deal with.

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Gary Martin
Gary Martin Veteran Member • Posts: 4,746
Thanks Gordon!

Based on your track record I would believe your conclusions. The K-7 essentially addresses the shortcomings of the K20D: Faster, quieter, better built, better design, better live-view, better LCD display, better viewfinder, HD movies, etc. Although it might not be quite as good as the state-of-the-art for APS-C in regards to noise (noticeable only at pixel-peeping levels, of course), it will produce nice, big, sharp files that when printed will look as good as anything else on the market.

But those hoping for a big jump in image quality over the K20D are going to be disappointed. I suspect that most of these are users who have been tempted by full-frame, and were hoping that the K-7 would perform some sort of miracle for APS-C. Not going to happen anytime soon!

Still, the K-7 continues to be a camera I lust after, and hope to purchase at some point when I'm done with my own LBA.

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exdeejjjaaaa
exdeejjjaaaa Veteran Member • Posts: 8,263
Re: Thanks Gordon!

Gary Martin wrote:

were hoping that the K-7 would perform some sort of miracle for APS-C.

just getting even w/ competition in the sensor department, nothing more was expected...

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exdeejjjaaaa
exdeejjjaaaa Veteran Member • Posts: 8,263
Re: Production K-7 Dynamic Range vs. K20D...

moving_comfort wrote:

jamesm007 wrote:

Samsung rebuilt the sensor from the ground up and the engineers could not find even a 5% improvement in dark read noise.

I keep seeing this repeated in various ways, and it's not really true - it's basically the same sensor core with reworked sensor peripherals (to vastly simplify it.)

Not "rebuilt from the ground up," although that would have been nice... You can only do so much about noise working with basically the same sensor.

you still have 5 FPS w/ a focus on a static subject and video...

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OP GordonBGood Veteran Member • Posts: 6,311
Re: Production K-7 Dynamic Range vs. K20D...

Bart Hickman wrote:

Sensor revisions must cost a fortune--I'd figure at least a $1 million.

On the other hand, if image quality were up there with the biggies, there might be 100's of millions of dollars gained in market share.

I'm curious--do you think the limitation is still due to a preamplifier in front of the ADC?

Yes, I think it is still primarily the variable gain amplifier in front of the ADC that is implemented on the sensor, although it appears with the 4 channel K-7 sensor that there is also quite a lot of black read sensor noise as well.

Regards, GordonBGood

BravoBrown Senior Member • Posts: 1,046
Re: Production K-7 Dynamic Range vs. K20D...

Hi Gordon,

Lots of people have been looking forward to your thoughts about the production K7. Glad to hear you liked nearly all of the improvements on the new cam. Too bad the noise/DR point you're interested in hasn't improved. Of course, not everyone is after the same thing. If we all bought cameras only for one certain aspect, we'd all be buying the exact same thing, right?

I'm curious about the reports I've been reading as to the K7 being cleaner in dark shadows, as that sounds like the opposite of what you're saying. Are they talking about something different? Maybe that's just about NR or banding. I suppose if that's really the most important thing to someone there are other cameras better suited to their purposes. Evidently the reworking of the sensor was just for live view/movie capabilities without major detriment to photo IQ. I guess that's still a step up, just not in the area you hoped for. Hopefully, in future iterations Pentax/Samsung will be able to close the gap with Nikon type noise control at the source.

Being able to pull up shadows without introducing objectionable noise would definitely be nice. Maybe with these new Samsung CMOS sensors folks will have to get used to exposing to the right more like the Canon folks do. Of course no one in normal use will be pulling shadows up 7 stops, but I personally would like to know HOW much you can pull up the shadows without detrimental noise. In extreme DR situations, there are always the HDR type techniques, but if proper metering/exposure will still allow some push processing without a mess of things, I'll be happy. No matter what camera, you learn to live with its limitations. Despite your assurance, samples of how much push processing the files can stand would still be nice to further back up your findings so folks can decide whether or not the difference will be practical to their needs.
Thanks for the tests and info.
Best regards,
Mark

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viking79
viking79 Forum Pro • Posts: 14,156
Re: Thanks Gordon!

exdeejjjaaaa wrote:

Gary Martin wrote:

were hoping that the K-7 would perform some sort of miracle for APS-C.

just getting even w/ competition in the sensor department, nothing more was expected...

But was the other sensor worse? DxOMark rates the K20d better than the 50d sensor, all things considered.

Eric

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OP GordonBGood Veteran Member • Posts: 6,311
Re: Production K-7 Dynamic Range vs. K20D...

solarider wrote:

In your estimation, is this problem due to hardware or firmware or a combination... does a firware fix have any chance of improving the picture? pun not necessarily need to be intended ];-)

I believe that the problem is due to the hardware on the sensor itself and thus can't be fixed by firmware other than to mask it with Noise Reduction (NR), which the in-camera JPEG development no doubt does (Standard NR by default).

Regards, GordonBGood

exdeejjjaaaa
exdeejjjaaaa Veteran Member • Posts: 8,263
Re: Production K-7 Dynamic Range vs. K20D...

GordonBGood wrote:

Bart Hickman wrote:

Sensor revisions must cost a fortune--I'd figure at least a $1 million.

On the other hand, if image quality were up there with the biggies, there might be 100's of millions of dollars gained in market share.

not gonna happen - as we mostly will like sheeps buy K-7 (few sooner, more later) so are others not going to join us en masse even if you will have what some people were hoping for... people who are buying or not buying K-7 from other camps, are certainly not buying or not buying it for sensor, for as long as it is not as lags behind each and every sensor on the market and it definetely not and for as long as it not FF, which again it is not - so it is not what they pay serious attention to...

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OP GordonBGood Veteran Member • Posts: 6,311
Re: Production K-7 Dynamic Range vs. K20D...

BravoBrown wrote:

I'm curious about the reports I've been reading as to the K7 being cleaner in dark shadows, as that sounds like the opposite of what you're saying. Are they talking about something different? Maybe that's just about NR or banding.

Perhaps the in-camera development has steeper Tone Response Curves (TRC's), which would mask the problem or more noise reduction is being applied by default

Being able to pull up shadows without introducing objectionable noise would definitely be nice. ...Of course no one in normal use will be pulling shadows up 7 stops, but I personally would like to know HOW much you can pull up the shadows without detrimental noise

Mark, it is likely reasonable to boost the shadows about 2.5 stops for ISO 100 and perhaps about 1.5 stops for ISO 200 for very good to excellent image quality. The new Nikon CMOS APS-C cameras can likely be boosted about a stop more for the same quality.

I wasn't saying that I recommend boosting shadows by 7 stops, just the 7 stops below bright level was the level that I did my dark shadow noise measurements.

Regards, GordonBGood

exdeejjjaaaa
exdeejjjaaaa Veteran Member • Posts: 8,263
Re: Production K-7 Dynamic Range vs. K20D...

GordonBGood wrote:

Mark, it is likely reasonable to boost the shadows about 2.5 stops for ISO 100 and perhaps about 1.5 stops for ISO 200 for very good to excellent image quality.

off topic :: curiously CaptureOne designed to have exposure slider in its user interface to allow + - 2.5 EV

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Gary Martin
Gary Martin Veteran Member • Posts: 4,746
Re: Thanks Gordon!

were hoping that the K-7 would perform some sort of miracle for APS-C.

just getting even w/ competition in the sensor department, nothing more was expected...

It's close enough, IMO.

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