Highlight Tone priority of 40D with LR 1.3

[ranjans]

Does LR honor the HTP tag in the 40D raw file & make use of it in producing smoother detailed highlights?
Or is it only DPP which makes use of this feature.

[madmanchan]

Yes, LR interprets it fine. See post here by Thomas Knoll:

http://adobeforums.com/webx?128@@.3c0330d0

(That discussion is about ACR, which LR uses.)

[chickenhawk212]

Yes, LR interprets it fine. See post here by Thomas Knoll:

http://adobeforums.com/webx?128@@.3c0330d0

(That discussion is about ACR, which LR uses.)
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Thanks for providing the link madmanchan, I was sort of hoping that HTP did something a little more useful than just exposing one stop to the left...im also a bit confused how exposing one shot to the left would make "the gradations between the grays and highlights smoother" as quoted from my 40d manual.  As i understand it (and maybe i dont) as long as you dont blow out any of the channels, exposing to the right would make tonal gradations smoother, not exposing to the left.  And why is iso 100 not available if all that is happening is simply 1 stop underexposure?  Am i confused about exposure or is canon trying to trick me into thinking they provided a useful tool with HTP?  

[Slobodan Blagojevic]

...I was sort of hoping that HTP did something a little more useful than just exposing one stop to the left...

It does, if you are shooting JPEG: it adds a different tone curve to open up the mid-tones and shadows. Not that you could not come up with the same (or better) curve yourself though. In RAW it does nothing, except underexposing one stop.

... as long as you dont blow out any of the channels, exposing to the right would make tonal gradations smoother, not exposing to the left...

Correct, except for the "as long as you don't blow out any of the channels..." part. Well, how do you make sure you are not blowing out any of the channels? Only by underexposing, and that is exactly what HTP does.

... And why is iso 100 not available if all that is happening is simply 1 stop underexposure?...

Well, because you are already at iso 100, i.e., that is how the underexposure is achieved. In other words, HTP does not change shutter speed/f-stop combination, it simply uses one step lower iso, so if your starting point was iso 200 (the minimum for HTP), it actually shoots using iso 100.

[chickenhawk212]

Thanks Slobodan, thats really helpful.  I only shoot raw and usualy bracket my exposures so i guess i wont be needing HTP.  Any insight you might have about high iso speed noise reduction with RAW shooting would be appreciated.  Thanks!

Chris

[drgreenberg]

Well, because you are already at iso 100, i.e., that is how the underexposure is achieved. In other words, HTP does not change shutter speed/f-stop combination, it simply uses one step lower iso, so if your starting point was iso 200 (the minimum for HTP), it actually shoots using iso 100.
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When you shoot ISO 200 in HTP mode, you're still exposing using ISO 200. That is, the shutter speed/aperture combo is that which is correct for ISO 200. However, the analog gain applied to the sensor signal is that of ISO 100. That's why you are limited to ISO 200. To shoot ISO 100/HTP would require an ISO 50 analog amp, which the camera doesn't contain.

Equivalently, ISO 200/HTP is exactly the same as ISO 100/no HTP/EC = -1, as far as the raw is concerned (except for the minor matter of how the mode is logged in the metadata, to inform DPP what the camera did).

David