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09-03-2014, 06:01 AM   #16
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QuoteOriginally posted by southlander Quote
we can discount face detect as having any influence
Note the presence of working face detection in the K-3 EXIF for image 2 WITHOUT LIVE VIEW BEING ACTIVE:
QuoteQuote:
Face Detect : On (5 faces max); 1 faces detected
Face Detect Frame Size : 0 0
Also note that the Nikon D800, with it's 91k metering sensor (only slightly more detailed than the K-3's 86k unit), also does stuff like:

"exposure control considering face brightness is achieved by the enhanced face detection performance of Advanced Scene Recognition System", "Auto-area AF detects human faces and prioritizes their sharpness" and here "The RGB sensor with approximately 91K (91,000) pixels built into the D800/D800E offers more accurate face detection. When used with viewfinder framing in exposure modes other than M, the camera balances exposure between a portrait subject and the background, even when the subject is backlit.."

So it seems not impossible for the K-3 to do a similar sort of job as the D800, given the similarity of the metering hardware. Pentax (perhaps) just hasn't disclosed this capability yet for K-3 PDAF. Maybe it's still v0.5 beta code, or something they are reserving as a listed feature for a future camera.

---------- Post added 2014-09-03 at 11:03 PM ----------

QuoteOriginally posted by savoche Quote
Yes, I was wondering, too, if there could be a metering face detection algorithm - not at all related to the live view focus face detection.
That's what I've been saying.

Something along the lines of this:



Last edited by rawr; 09-03-2014 at 06:10 AM.
09-03-2014, 01:59 PM   #17
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QuoteOriginally posted by southlander Quote
Reading the K-3 manual, it looks as though Face Detect autofocus is only available in Live View (as Adam indicated in his response). Thus it would seem we can discount face detect as having any influence on the OP's experience with the two posted images. I'm back to pondering the AE-L or Link AE with AF Point settings on Custom settings area of the camera's menu. Or whether the differences in lighting between shot 1 and 2 was simply enough to trigger the camera to go down a different logic path (eg in shot 2 the proportion of very dark to very light was enough for the camera to assume a backlit scene where as in shot 2, it didn't see enough of this to trigger the back lighting logic. Overall, I'd say the lighting found in the OP's situation was not easy for a camera to determine what was required and would be the sort of scene where exposure bracketing could be helpful..
Is face detect AF in anyway related to face detect exposure ?
I would think there two seperate systems and not related.
09-03-2014, 02:08 PM   #18
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QuoteOriginally posted by southlander Quote
Reading the K-3 manual, it looks as though Face Detect autofocus is only available in Live View (as Adam indicated in his response). Thus it would seem we can discount face detect as having any influence on the OP's experience with the two posted images.
Agreed. I did a fair amount of testing since yesterday and while there may be entries at the addresses associated with face recognition within the exif when the camera is not in live view, those entries do not conform to the format used for the feature. It appears the addresses may document other features when not in live view and the authors of ExifTool has not yet deciphered what that purpose might be.*


Steve

* ExifTool uses friendly labels (tags) for the the maker-specific exif entries. Those labels don't exist in the raw files, just in the ExifTool output. The FaceDetect, FaceDetectFrameSize, FacesDetected, and FacePosition tags fall into that category. Sometimes the ExifTools authors' analysis is good and sometimes it is less than good.

---------- Post added 09-03-14 at 02:21 PM ----------

QuoteOriginally posted by rawr Quote
Note the presence of working face detection in the K-3 EXIF for image 2 WITHOUT LIVE VIEW BEING ACTIVE:
QuoteQuote:
Face Detect : On (5 faces max); 1 faces detected
Face Detect Frame Size : 0 0
I know that it looks like compelling evidence of an undocumented feature and it may well be, but I did extensive testing yesterday and was unable to get automatic exposure compensation when the value for FaceDetect was 5 1 (interpreted by ExifTool as "On (5 faces max); 1 faces detected"). I also did an audit of my K-3 photos and found that the camera did indeed see faces a good bit of the time where faces were present (<20%) and did not see faces where they were not. Something may be going on, but probably not anything that would explain the OPs experience.

It occurred to me as well, that the exif entries may be intended as instructions for post-processing by a Pentax-smart RAW converter.


Steve

Last edited by stevebrot; 09-03-2014 at 02:47 PM.
09-04-2014, 01:16 AM   #19
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QuoteOriginally posted by stevebrot Quote
I know that it looks like compelling evidence of an undocumented feature and it may well be, but I did extensive testing yesterday and was unable to get automatic exposure compensation when the value for FaceDetect was 5 1 (interpreted by ExifTool as "On (5 faces max); 1 faces detected"). I also did an audit of my K-3 photos and found that the camera did indeed see faces a good bit of the time where faces were present (<20%) and did not see faces where they were not. Something may be going on, but probably not anything that would explain the OPs experience.
Thanks for spending time diving into this. You also helped me out a lot with my "early shutter penalty" question. Much obliged.


Did you try specifically with backlit faces? I'd suppose the multisegment metering with face detection (if that's what is going on at all) would only be noticeable when the face was too dark?


I really ought to experiment myself. It should be an easy test: Set someone up in a backlit situation, snap when they cover their face with their hands and when they don't. Compare the two.


Regards,
--Anders.

09-04-2014, 06:05 AM   #20
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As I understand it this was an in camera jpeg, so isn't it possible that the camera detected the face after the shoot was made and then pushed the exposure when converting to jpeg?
09-04-2014, 06:47 AM   #21
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QuoteOriginally posted by Gimbal Quote
As I understand it this was an in camera jpeg, so isn't it possible that the camera detected the face after the shoot was made and then pushed the exposure when converting to jpeg?
That's quite possible and, in fact, isn't that how Green mode works? My impression (and I may be wrong) is Green mode is simply a JPEG scene selection algorithm for in-camera processing.
09-04-2014, 07:06 AM   #22
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QuoteOriginally posted by Gimbal Quote
As I understand it this was an in camera jpeg, so isn't it possible that the camera detected the face after the shoot was made and then pushed the exposure when converting to jpeg?
I don't think so because the ISO changed from ISO 160 (no face) to 640 (with face).


It is of course possible that the ISO reported in the EXIF reflects some kind of JPEG shadow lift. I just believe it's unlikely.


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09-04-2014, 07:32 AM   #23
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QuoteOriginally posted by asp1880 Quote
Did you try specifically with backlit faces?
Yes, I did.

QuoteOriginally posted by Gimbal Quote
As I understand it this was an in camera jpeg, so isn't it possible that the camera detected the face after the shoot was made and then pushed the exposure when converting to jpeg?
Anything is possible, though I am not aware of such a trick and was unable to reproduce.

QuoteOriginally posted by IchabodCrane Quote
That's quite possible and, in fact, isn't that how Green mode works? My impression (and I may be wrong) is Green mode is simply a JPEG scene selection algorithm for in-camera processing.
Now that is something I had never heard before. I knew that Green mode was basically auto-everything, but was not aware that the K-3 supported auto scene selection. How would that work with RAW output?

As for the OP's photos, they were shot in Tv mode and the exif indicates scene as "normal" with "normal" processing. If something sneaky was happening, it is not reflected there.


Steve

09-13-2014, 11:42 AM   #24
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This just looks like the Pentax "Real-Time Scene Analysis System" at work here.

From what I can tell, the camera seems to be using a modified version of the Live View metering algorithms when shooting through the viewfinder, enabled by the 86k pixel RGB metering sensor and PRIME III processor. It really seems the K-3 is a lot smarter than previous Pentax cameras...

--DragonLord
09-13-2014, 11:59 AM   #25
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QuoteOriginally posted by DragonLord Quote
This just looks like the Pentax "Real-Time Scene Analysis System" at work here.
Were you able to reproduce it? I was not without having the exposure follow the focus point.


Steve
09-13-2014, 12:05 PM   #26
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QuoteOriginally posted by stevebrot Quote
Were you able to reproduce it? I was not without having the exposure follow the focus point.


Steve
I don't own a K-3, but I think the camera is simply operating as advertised here.

--DragonLord
09-13-2014, 06:55 PM   #27
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QuoteOriginally posted by DragonLord Quote
I don't own a K-3, but I think the camera is simply operating as advertised here.

--DragonLord
Hmmmm...I too believe the camera did what it was supposed to, but I don't believe it is a magical undocumented feature. At least the camera on the table behind me has not revealed these qualities. If it does support some sort of advanced scene-specific evaluative metering, it must be VERY poorly implemented. My understanding of the "Real Time Scene Analysis" system is that its strong point is to differentiate color, intensity, and pattern from the viewfinder image. According to Ricoh, this allows:
  • Enhanced white balance analysis
  • More accurate subject tracking for AF purposes
  • More reliable and precise AE function
The way I read the text and diagrams*, it uses scene detection in the rough sense of the term. That being said, it has the potential to do great things, though I don't believe any of them are implemented in the current model K-3.


Steve

* Feature 1?K-3 | RICOH IMAGING (bottom of page)
09-19-2014, 07:32 AM   #28
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QuoteOriginally posted by aleonx3 Quote
If you have this setting "Link AE to AF point" set to ON for multi-segment metering, then the exposure may change due to the focus point changed (in this case, perhaps, the face).


Hit the nail on the head right there.


Even when using multi af points, the camera still chooses only one to use, and I am not completely sure what makes it choose. I've put my camera on a tripod and hit the AF button and watched the red box appear in a different location every time I pushed that button - even when nothing in the scene has changed.


If you were using a single AF point, I think you would have gotten more consistent results.

---------- Post added 09-19-14 at 07:40 AM ----------

QuoteOriginally posted by awaldram Quote
Is face detect AF in anyway related to face detect exposure ?
I would think there two seperate systems and not related.


Face detect AF is indirectly connected to exposure. If the camera is set to lock AE point to AF point, then the metering will prioritize based on the AF point, which is linked to face detect if that feature is turned on.


Whether face detect is off or on seems to have no effect on center focus point or selective focus point, but only on auto focus point modes.
09-19-2014, 07:57 AM   #29
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QuoteOriginally posted by chimpwithagun Quote
Hit the nail on the head right there.


Even when using multi af points, the camera still chooses only one to use, and I am not completely sure what makes it choose. I've put my camera on a tripod and hit the AF button and watched the red box appear in a different location every time I pushed that button - even when nothing in the scene has changed.


If you were using a single AF point, I think you would have gotten more consistent results.[COLOR="Silver"]
It is true... the camera cycles through the "possible focus-area", so it may not land on the same spot when you hit AF (or half-press) every time. That's why it is better to select your focus point instead of letting the camera to choose.

Last edited by aleonx3; 09-19-2014 at 08:06 AM.
09-19-2014, 09:23 AM   #30
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QuoteOriginally posted by chimpwithagun Quote
Hit the nail on the head right there.


Even when using multi af points, the camera still chooses only one to use, and I am not completely sure what makes it choose. I've put my camera on a tripod and hit the AF button and watched the red box appear in a different location every time I pushed that button - even when nothing in the scene has changed.


If you were using a single AF point, I think you would have gotten more consistent results.

---------- Post added 09-19-14 at 07:40 AM ----------





Face detect AF is indirectly connected to exposure. If the camera is set to lock AE point to AF point, then the metering will prioritize based on the AF point, which is linked to face detect if that feature is turned on.


Whether face detect is off or on seems to have no effect on center focus point or selective focus point, but only on auto focus point modes.
Face detect AF is only available in LV mode.
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