Author Topic: Dual iso like canon highlight tone priority  (Read 2822 times)

netocg

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Dual iso like canon highlight tone priority
« on: January 30, 2018, 09:27:43 PM »
Hi all,

I don't know if everyone is familiar with the canon feature highlight tone priority, but basically the camera shoot a lower iso for u and blend with your picture so you have more details in the highlights instead of such a clamped or burned ones.

Would be nice if dual iso feature could avoid the post-process step and get the shadow details back blended to your picture.

josepvm

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Re: Dual iso like canon highlight tone priority
« Reply #1 on: January 31, 2018, 08:42:51 AM »
That's not the way it works. Canon"s HTP does not blend exposures, it makes a single shot, but lowers the exposure value to preserve highligths, at the expense of having more noise in the shadows.

And it has been explained many times in this forum that the postprocessing of DualISO images cannot be done in camera, because it requires intense computation, and that's too much work for the tiny embedded ARM processors our cameras have.

kyrobb

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Re: Dual iso like canon highlight tone priority
« Reply #2 on: January 31, 2018, 09:25:20 PM »
If you like HTP, just use it. The way I understand it, HTP just pushes the shadows. So when your camera reads 200D+ iso, it's actually 100 iso with the shadows pushed 1 stop. You could do this yourself with raw video. Just underexpose your image by one stop, then lift the shadows in post.

josepvm

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Re: Dual iso like canon highlight tone priority
« Reply #3 on: January 31, 2018, 09:58:16 PM »
HTP reduces exposure (by lowering ISO) in one stop to preserve highlights.  I you shoot raw, this is the only effect you see, a reduced exposure. If you shoot jpg the camera also pushes the shadows (using a modified tone curve to develop the jpg in camera), but, as a side effect, the shadow noise gets pushed, too. There is no improvement in dynamic range.

So yes,  If you shoot raw you can do the same reducing the exposure to avoid clipping highlights (Magic Lantern's AutoETTR module is a highly accurate tool to do this) and pushing the shadows in post.

kyrobb

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Re: Dual iso like canon highlight tone priority
« Reply #4 on: January 31, 2018, 10:08:06 PM »
Yes exactly. I was speaking more in reference to h.264 video, which would be the same as jpeg. But yeah HTP will have no effect on raw.

My point is that HTP lies to you. It tells you you're shooting in a higher iso than you really are. It drops one stop for the highlights, and then pushes the shadows one stop to keep them the same. Increased noise is one result. You get a perceived increased dynamic range, but it's not real. Just shoot raw if you can.

netocg

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Re: Dual iso like canon highlight tone priority
« Reply #5 on: January 31, 2018, 10:38:00 PM »
I didn't know that htp was fakeing the feeling of have my highlights shoot at a lower iso. Interesting to know that is actually doing the reverse, shooting at the lower and then just rising luminance perception of the shadow areas.
That's what I understand from your explanation.
It make sense why when I look to the raw the image contracts doesn't look as it was in the "same lighting conditions" of the JPG shooting.