Gear Talk > EOS Bodies - For Stills
What is "highlight tone priority" good for anyway?
markIVantony:
Bosman might have been replying to your title, which is a bit different than the ISO question you ask.
Regarding ISO, raising the minimum ISO might be to provide a buffer range for the firmware to allow -up to- a 150 ISO reduction in the entire image, and then to have room to shift the non-highlights back up to the original values before writing the image values. Else, you could lose the black values (they would become less than zero). However, I can only imagine there are several other equally effective algorithms to give highlight tones priority.
Jake Townsen:
HTP used with raw obviously helps retain a lot more detail in the highlights. I could complelty blow out a shot where a wedding dress has no information and recover 90% of the detail in post. Without HTP a lot of that detail is lost. From what I understand the reason iso 200 is used is because iso 100 is a computerized iso, kind of like iso 50. Whereas iso 200 is more native and able to record more information layers. Thus allowing more leeway when recovering highlights. Actually when I've used iso 50 I've noticed how much less information is recorded in the raw. Check the camera manual as i recall there is something written about this, probably explains it better than I can.
keithfullermusic:
Maybe I'm totally wrong, but I thought it exposes for the highlights at ISO 100 and exposes everything else at 200.
Everything I've heard about it is that you really shouldn't use it unless you're shooting jpeg because you can do it in post, and probably a better job, but you have to make sure to expose for the highlights.
Marsu42:
--- Quote from: keithfullermusic on April 15, 2012, 01:01:33 PM ---Maybe I'm totally wrong, but I thought it exposes for the highlights at ISO 100 and exposes everything else at 200.
--- End quote ---
First time I've read that, but it would explain the iso increase... sources?
--- Quote from: Jake Townsen on April 15, 2012, 12:57:32 PM ---HTP used with raw obviously helps retain a lot more detail in the highlights. I could complelty blow out a shot where a wedding dress has no information and recover 90% of the detail in post. Without HTP a lot of that detail is lost.
--- End quote ---
The 60d manual? Explaining about inner iso workings? Not really :-) ... I'll get this information from magic lantern, in the latest builds you can separately tune the analog iso and digic digital gain (only full ev steps are native, the other ones are a hack I'm only using when shooting m with auto iso). But you're basically saying that there is a "real" data difference between htp and vanilla shots, and not just a reversible tone curve?
Mt Spokane Photography:
--- Quote from: Marsu42 on April 15, 2012, 12:33:24 PM ---
--- Quote from: Mt Spokane Photography on April 15, 2012, 12:30:02 PM ---The setting is usually not used by raw processors except for DPP, so it has no effect on raw images for most photographers. Its just a trigger telling DPP to apply a exposure curve to the raw image as it processes it, no harm done, you can change the curve any way you like.
--- End quote ---
This is interesting and unexpected (and still doesn't explain the raised iso) because Adobe raw in Lightroom does the same thing. I really expected that htp alters the actual raw data, too. It might be futile to ask but are you 100% sure about this? Any sources?
--- End quote ---
I turn it off for Raw, and forgot about the ISO change. There seems to be a lot of opinion as to what curves image editors apply or don't apply, and no authoritative agreement. We know what happens in jpeg.
In raw, unless you use DPP, I'd turn it off, and even if you use DPP, its a matter of personal opinion as to its benig better or not.
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I think you have brought up a good point, and its likely that each raw processor handles the situation differently as far as if or how they apply the tone curves.
I might try it with lightroom 4 RC1 and see what differences it makes, but I do not know if i'd be able to see any tone curves applied.
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