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05-10-2015, 08:55 AM   #1
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Blinkies - just misleading (on K-3 using RAW)

I finally got round to testing something I'd long suspected ... the histogram and blinkies (on K-3) are very misleading/conservative. I knew they were and found I was instinctively adding extra positive exposure compensation to many shots. However, I wanted to properly quantify my suspicions.

Shooting in RAW (this post is not relevant if shooting in JPEG), I took a series of shots at various lighting conditions, from dull, to high contrast and with various exposure compensations and different ISO settings. I then processed them in ACR (latest process model - this is key, as it works better than 2010 version) so they were all exposed to the same extent (setting the images to taste). I then pulled back the highlights till the ALT/slider showed no clipping. I used exposure compensations from 0 to +1.7 initially, before settling on testing 0 and +1.0 in subsequent tests. In ALL cases I could control the highlight clipping at +1.0.

It was evident from the beginning that +1.0 was entirely safe to over expose in all the tests I ran. At higher ISO is was even more reliable, than at ISO 100.

Then the interesting part... by exposing "to the right" and comparing noise levels of images that were exposed at 0 compared to 1.0, it became apparent that images that were viewed at effectively the same exposure on screen (ie the 0 shots with +1 exposure added in ACR), then the noise was better in the shots taken at +1.0. This is explained by more data being captured at the brighter levels by the sensor. With increasing ISO, "over exposed" images showed a markedly better noise result when processed.

Finally, putting the SD card back into the camera and making comparisons between the JPEG histogram on the camera and the before/after histograms in ACR, revealed how different the results were and how misleading the blinkies are too.

So I have set all my user settings on +1.0 for now.

(I ran the same on my Ricoh GR, and got similar results, and so have my user settings set there to +1.0 as well. Though as the dynamic range of this sensor is less than the K-3, I am not so convinced this will work as well in extended usage)

I guess there may be more processing involved, and perhaps some risk of the occasional highlights being permanently clipped (could always just bracket), but the IQ does seem to be consistently better using this technique. One extra exposure stop makes slow shutter speeds a little more risky, of course. As mentioned the latest version of ACR uses a better process model than earlier versions. I compared with 2010 process model, and did not see anything like the highlight control available from the older version.

Anyone else defaulting to something like +1.0 ?

05-10-2015, 09:07 AM   #2
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My experience would agree with this. I generally adjust compensation so that the brightest area of the image, white cloud for example, has some blinkies in it. There is no problem pulling back +1 stop in Lightroom. Your observations on noise are also spot on. Much better to pull back the highlights a bit than to pull up the shadows because even though you can pull them up those areas will have more noise. I don't use +1 but I do usually use +2/3 stop.
05-10-2015, 02:21 PM   #3
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1. Usually you can expose about 2/3 to 1 e.v. greater w/ raw than w/ jpg--because two channels of data not overexposed allow the third channel to be estimated (anyway that is what photoshop does).
2. And there is a second effect--the jpeg will be somewhat overexposed as compared to all three channels OK in raw--likely on the order of a few tenths of an e.v..

Of these the item 1 will not often be very accurate--so the colors may be off. So this is something you should not do automatically.
The second one is likely limited by the computer resources in the camera, and because many shooters use jpj--and thus a jpg and not raw data is used.

BTW I use PS CS2 and find the available headroom to be about 2/3 stop typically--so it is not just latest ACR
05-10-2015, 05:36 PM   #4
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What scene mode do you have the JPEGs on your camera set to? I believe the histogram (and blinkies) follows the selected JPEG Scene type in determining the brightness values to graph. So if you have a JPEG scene set to Bright for example, the histogram shows the effects of the boosted JPEG contrast and saturation. As I shoot RAW always, I set the JPEG mode to Natural which doesn't give much boost to either contrast or saturation. The histogram is then a much more accurate indication of what is going on at the point of image capture and in respect of the resultant RAW file contents.

Even shooting RAW, the JPEG processing is active. Each RAW file has an embedded JPEG within it, this JPEG is processed to the scene mode active at the time the image is captured.


Last edited by southlander; 05-10-2015 at 05:42 PM.
05-11-2015, 12:57 AM   #5
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Ref the Scene setting... I tried various. The histogram does change with the Scene as expected, however the blinkie/highlight clipping remains much the same. So it doesn't give the high end info I am seeking. Defaulting to Natural is probably better to reflect the image data more appropriately. Thanks Southlander.

Ref the PS processing of the 3 channels when one or more is clipped (thanks DMS), I was aware of this but in all honestly the software does such a great job that I could not spot any artifacts or colour shifts that might be a problem. As noise is improved, in many cases, I guess this is a balance.

I'll probably bracket at first, though I wish I could bracket with MUP, and see what happens. Maybe +2/3 is wiser ...
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