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Old January 2nd, 2009, 11:39 PM   #1
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Highlight Tone Priority

I was testing some of the image settings today and found that when enabled, Highlight Tone Priority increases the dynamic range into the highlights by about one stop in video mode.

It brings out details in highlights (skies, whites, lights, etc) without adding any noise. I'm not sure what its doing, I don't think its just underexposing by one stop. I tried to lower the exposure but it was not the same result. I'm guessing its some operation on the raw data or some sensor feature. Please correct me if I'm wrong.

The other benefit discussed a while back is that it allows you to adjust your shutter speed at ISO 200 instead of 100.
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Old January 3rd, 2009, 12:00 AM   #2
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It brings out details in highlights (skies, whites, lights, etc) without adding any noise.
HTP drops the ISO by one stop and use +1 compressed exposure compensation to get back the brightness while preserving highlights.

Read noise in the 5d2 is highest at ISO 100, then decreases until 1600, with no change after that. The reason you don't see any additional noise is threefold:
  • 5d2 video has a lot of heavy noise reduction, even with NR: "off" in the camera.
  • 5d2 video has a very high black point and the default picture styles crush blacks further
  • HTP fixes the broken ISO 3200 mode (by not deleting the highlights)
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Old January 3rd, 2009, 12:18 AM   #3
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[*]5d2 video has a very high black point and the default picture styles crush blacks further
The default picture style is indeed by far to contrasty.
Even contrast at lowest setting -4 is not too dull, and you have to reduce the colors too (-2 might be a good starting point).

BUT: The default picture style doesn´t really crush blacks, it just compresses them too strong into an area of the RGB 0-255 colorspace that most applications do not import properly!
With MOV, the majority of programs recognise only the RGB 16-235 values and everything below 16 is lost.
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[*]HTP fixes the broken ISO 3200 mode (by not deleting the highlights)[/list]
What is the broken ISO 3200 mode? Did I miss something?
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Old January 3rd, 2009, 12:35 AM   #4
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The default picture style is indeed by far to contrasty.
Even contrast at lowest setting -4 is not too dull, and you have to reduce the colors too (-2 might be a good starting point).
Yes, I'm still trying to find a picture style that has the right contrast and colors for my purposes. Been shooting Canon for years, but I have to learn their picture style system from scratch since I shoot raw. I'm not doing very well so far, as I get really funky skin tones when I try to build a low contrast curve or use negative contrast settings.

Quote:
BUT: The default picture style doesn´t really crush blacks, it just compresses them too strong into an area of the RGB 0-255 colorspace that most applications do not import properly!
I'm using the CoreAVC workaround for now and the amount of detail in those last 0-16 is pretty tremendous, but there is still a lot more underneath that which is crushed by the black point and curve. Hopefully I will get it all back with the right picture style.

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What is the broken ISO 3200 mode? Did I miss something?
It's a little known problem with many digital cameras. ISO 3200 has the same read noise as ISO 1600, so the only difference between ISO 1600 and ISO 3200 is that the latter has one stop less highlights. ISO 6400 is even worse: its highlights are literally deleted from the file, digitally, for no reason (for a 2-stop loss in highlights). 25600, similarly, loses 4 stops of highlights for no reason. Highlight tone priority is the correct solution to this problem since it performs applies a curve to the highlights so that they are preserved instead of deleted. Unfortunately, Canon disabled HTP for ISO 6400+, and they only made it effective for 1 stop (an optional 4 stops would have been correct, so it could be used for all ISO settings). At least it works for 3200, so that we can at least use it to fix that one.
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Old January 3rd, 2009, 10:23 AM   #5
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It was not obvious in the scene I tried last night but this morning I found that it does in fact increase visible noise. It still may be useful but you would have to make a compromise.
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Old January 3rd, 2009, 02:01 PM   #6
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It was not obvious in the scene I tried last night but this morning I found that it does in fact increase visible noise. It still may be useful but you would have to make a compromise.
I was test shooting a concert situation, and the bad thing is:
HTP does increase the vertical banding issue!
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Old January 3rd, 2009, 02:11 PM   #7
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Yes, I'm still trying to find a picture style that has the right contrast and colors for my purposes. Been shooting Canon for years, but I have to learn their picture style system from scratch since I shoot raw. I'm not doing very well so far, as I get really funky skin tones when I try to build a low contrast curve or use negative contrast settings.
Does the picture style editor allow more settings than in camera (e.g. negative contrast values)?
I think the "Standard" and "Neutral"-Picture style are the best, since Portrait and Landscape have weird colors. I prefer the standard-style since neutral has purplish blues.
With both the lowest in cam setting of -4 seems best and you have to recuce saturation as well to at least -2. Sharpness of course at lowest possible setting.
But I have so far just tested in camera parameters when connected to the monitor.
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