Highlight Tone Priority and potential latitude improvement

[Scott Brickert]

According to the manual (p153) the Highlight Tone Priority function is available in Movie mode.

I wonder if it will act as more of a protection against blowing out highlights, i.e. sets the exposure based on the brightest part of the frame, thereby likely crushing the shadows, or functions as a sort of regional gain control, retaining shadow detail while retarding or applying 'negative gain' in the highlights to prevent them from clipping....

[Evan Donn]

assuming it's the same as the 5D it basically underexposes by one ISO step then raises the shadows electronically, so it does protect your highlights but also brings up the visible noise in the shadows. I'm not really sure there's much benefit vs. just exposing for your highlights and lifting the blacks in post other than the fact that it happens prior to compression in camera. Might be an interesting experiment to compare the two methods.

[Glen Elliott]

I did some tests of my own with it on and off. The dynamic range is greatly improved with it on so I ALWAYS shoot with it on now.

PS Evan, where did you read that's how it works (ie electronically lifting blacks). I don't see any difference in my blacks, only the knee, or point which the highlights are blown.

[Don Miller]

Originally Posted by Glen Elliott

I did some tests of my own with it on and off. The dynamic range is greatly improved with it on so I ALWAYS shoot with it on now.

PS Evan, where did you read that's how it works (ie electronically lifting blacks). I don't see any difference in my blacks, only the knee, or point which the highlights are blown.

I think you will want to be cautious as ISO approaches 800. But it does seem to provide good protection on a camera that's doesn't give much help as far as proper exposure.

Most people with 5DII lower the default contrast too.

As far as crushed blacks, I feel this can be overrated in importance. The eye is drawn to bright, and black blacks adds punch to the bright. Not that the dark should be carelessly crushed, just that viewers are not normally searching for detail in the bottom third of the exposure. But blown highlights always tend to suck unless it's a high key kind of look.

[Don Miller]

Originally Posted by Evan Donn

assuming it's the same as the 5D it basically underexposes by one ISO step then raises the shadows electronically, so it does protect your highlights but also brings up the visible noise in the shadows. I'm not really sure there's much benefit vs. just exposing for your highlights and lifting the blacks in post other than the fact that it happens prior to compression in camera. Might be an interesting experiment to compare the two methods.

I think it's a question of if one CAN confidently expose for the highlights. In a less controlled environment it can be more of 'hoping' to expose for the highlights.

I'm curious on the 7D how auto ISO works in manual mode. It would be nice in some situations to use auto exposure with variable ISO.

[Daniel Browning]

Originally Posted by Evan Donn

I'm not really sure there's much benefit vs. just exposing for your highlights and lifting the blacks in post other than the fact that it happens prior to compression in camera.

It is far better than doing it in post.

Originally Posted by Glen Elliott

I ALWAYS shoot with it on now.

Me too. Most of the time I wish there was a two-stop HTP, because one stop of extra highlights is often not nearly enough.

Originally Posted by Glen Elliott

I don't see any difference in my blacks, only the knee, or point which the highlights are blown.

If you try reducing your contrast, then you'll see down into the shadows far enough to see the increase in noise from HTP.

Originally Posted by Don Miller

I think you will want to be cautious as ISO approaches 800.

Just the opposite! HTP is even more useful at high ISO, since the benefit from higher ISO decreases as ISO is increased. That is, going from ISO 100 -> 200 reduces read noise almost a full stop. And 200 -> 400, likewise, is a very large improvement. But above 400 the improvements get smaller and smaller, so there is less benefit to to increasing ISO

That is, of course, assuming the 7D performance is the same as all the Canons that came before. Here is a chart of how the dynamic range is affected by various ISO settings of 5D2 raw files:

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