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Forum: Photographic Technique
05-22-2019, 04:17 AM
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Image 1890 - 2 stops over what I consider ideal exposure and one stop clipped as far as I am concerned. Highlight reconstruction applied in Darktable.
I feel Highlight reconstruction has done a great job considering it is guessing the tonal ranges it applies to the clipped areas (which the literature freely acknowledges).
First time I have used it - may use it more in the future when I find I have stuffed up the exposures.
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Forum: Photographic Technique
05-22-2019, 03:47 AM
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GUB's red undies -- taken from image 1884 - the image I consider correctly exposed. Plus a 100% crop.
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Forum: Photographic Technique
05-22-2019, 03:35 AM
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I am a little bit confused - is one of those images in your gif supposed to be corrected?
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Forum: Photographic Technique
05-21-2019, 07:20 PM
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In this example he may actually do a fair job of it Steve. With the weave of the cloth presenting lots of samples of unclipped tonal range beside the clipped areas the computer can probably do quite a good job of guessing the values in the clipped areas. Because a guess job it is.
colour / highlight reconstruction in Darktable;
Color Reconstruction | darktable |
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Forum: Photographic Technique
05-21-2019, 06:43 PM
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So I checked the result using Pentaxs own camera utility 5. Chose the 2 stop overexposed image (1890) and set it at -2 EV to bring the histo out. Result is showing massive clipping similar to Darktable.
So once more I reiterate - would Pentax really have a couple of stops of dynamic range spare without utilising it in its own software?
I suggest that the highlight reconstruction being claimed is merely extrapolation of the existing tonal range (of lower valued pixels) utilizing the fully saturated pixels .
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Forum: Photographic Technique
05-21-2019, 03:08 PM
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Isn't the hue shift a bit of a giveaway that the greens and blues have continued amplification while the red is stuck at full saturation.?
Yes I can reshape the end of the histo with the Highlight reconstruction function but I suspect it is a random rearrangement of the full value red pixels.
Do you really think Pentax has kept a couple of extra stops of dynamic range up its sleeve in the image output without telling anyone?
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Forum: Photographic Technique
05-21-2019, 01:59 PM
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Darktable. Base curve and Highlight reconstruction and White Balance were left enabled. Disabling Base Curve did not make much difference to the point at which the histo clipped but rather just shifted the histo around. Disabling highlight reconstruction just made everything clip - I suspect it required input from the Dynamic Range - highlight correction from the camera to set its values but I had that switched off.
No JPG editing here - all screenshots of raw editing laid out in a jpg image courtesy of Gimp.
I am in no way suggesting that my meter is "hot"
What I have presented is evidence that in these conditions the meter can present 6 stops worth of different values for the same exposure. I expected it to be 2 to 3 stops as in film days but 6 stops !! -- I can guess the incidence exposure better than 6 stops.
I presume modern matrix metering can sense the tonal range in a mormal image and lay out the exposure more accurately. But in these black/white/red images there is no tonal range for the meter to work on. Using the spot meter will increase the likely hood of there being no tonal range.
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Forum: Photographic Technique
05-21-2019, 01:39 PM
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Tony W -- Here is the 7 test images for the test to establish clipping point. The 7th image was so clipped I didn't bother including it on the post. If you can't find a clipped red here then we are on different planets!
Have fun with Rawdigger.
Dropbox - reds - Simplify your life |
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Forum: Photographic Technique
05-21-2019, 03:12 AM
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The next test was to check out something I had suspected and it has proved to be a biggie for those trusting their camera meter especially those in “spot”mode.
Now we all know that the meters are tricked by black cats and snow. It has been that way since in-camera metering started.
So lets have a look at a colour wheel of fully saturated primary and secondary colours.These colours have to be treated like they are pure white – the slightest increase in exposure will clip them.
But the camera meter doesn’t give a hoot what colour they are but just cares about how much light is falling on the sensor.
So I was suspecting the meter was essentially seeing a greyscale of the colours.
Now have a look at the colour wheel once it is greyscaled – the reds and blues have ended up with a tone that is darker than the 18% grey that meters tend to calibrate to.
Could it be that the meter is metering red (and blue) this way and so giving a totally different exposure to them compared to how it would meter white.
So in this test I have set the camera to AV mode and let it choose the shutter speed.To state the obvious the incident light falling on these subjects remained constant so the correct exposure for one should be the same for all. But we also already know the meter will tend to over expose the black and unde rexpose the white.
Just to clarify, these are clothes on the clothesline plus a sheet of photocopy paper for white. The black woollen shirt would be a very effective black with no reflection.
I am pretty sure my very rough estimate of 18% grey has proven fairly accurate in the towel and so anyone understanding incidence metering would recognise that its exposure (1/50 sec) would then be correct for all subjects.
In conclusion, if I have got this right then it is fair to say that the meter will attempt to overexpose fully saturated red by about half a stop.
That is just about a guarantee of a clipped red.
Please note that the screenshot of the red appears to be not full saturation but the developed raw to jpg shows clear clipping.
This experiment is fully repeatable.
If you wish to dispute the results then repeat the test and show that I am wrong.
I have to say I was surprised how clear the result was.
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Forum: Photographic Technique
05-21-2019, 03:05 AM
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The next test is to try and see if varying the jpg settings change the displayed histogram.
I chose the three settings that I suspect may change things – Dynamic Range highlight correction, Custom Image, and White Balance.
I did not change the exposure settings of the camera.
I only had “auto”as a choice for highlight correction and it may be the exposure didn’t kick the correction in.
No visible change from changing Custom Image from Natural to bright.
But changing WB from daylight to cloudy shifted the histogram about 1/4 of a stop. But this is probably because the image was red dominant so warming it would have a big effect.
My conclusion is the settings do not create a significant change in the margin of error as tested in the first post above.
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Forum: Photographic Technique
05-21-2019, 03:02 AM
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It is late Autumn here – too late for any roses so I had had to resort to using a particularly bright red set of undies freshly bought to run a few experiments to find out the best way to present red tones in all their glory.
The first experiment is to try and see how to identify the clipping point of colours in the histogram and to get an idea of how much margin of error is in the on camera histogram.
Camera Pentax K-1
So the day is very cloudy with a very consistent light.
The camera is in manual mode.
WB Daylight
CI Natural
Hi Dynamic Range =off
I set the first exposure for the red Histogram to be just clear of the right handside.(Which is where I would normally place it.) First image
Then with each shot I increase the exposure by 1/3 of a stop.
After downloading into darktable I bring the exposure back accordingly so the Histograms can be compared.
So note the EV settings in each screenshot.
I can identify clipping in the 4th image (1\30 sec) and the spiking in the 5th shot is an absolute giveaway that clipping is well under way.
The clue in the 4this the front of the histogram is slightly more sawn off and the histo has moved slightly left.
So on that basis if I set exposure so there is a visible gap between the histogram and the Right side then I have a maximum of one stop of margin of error.
But that is on this individual example and it may vary with say a more contrasty or less contrasty image.
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