Highlight Tone Priority?

Discussion in 'Beyond the Basics' started by Hardrock, Sep 2, 2010.

  1. Hardrock

    Hardrock TPF Noob!

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    Does anyone use it? I have not used it but have read a little about it. to my understanding it increases the dynamic range of the sensor but adds noise to dark areas? Whats your thoughts and opinions?
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    I don't have a camera with that mode, but to my understanding, it's similar to auto mode, except that instead of setting the exposure to ---0--- on the meter, it increases the exposure to just before it would be blown out.

    This fits in nicely with the technique....Expose Right

    That sounds more like Nikon's D-Lighting...but I could be wrong.
     
  3. clanthar

    clanthar TPF Noob!

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    Hi,

    It does not increase the dynamic range of the sensor. It's a set of algorithms in the image processor that prioritizes the reduction to 8 bit JPEG for highlight detail. It does not effect RAW files.

    In high contrast lighting conditions it is very possible to have more tonal information than the sensor is capable or recording. The sensor is capable of recording more tonal information than can be retained in an 8 bit per channel RGB image. Tonal information then must be compressed and discarded to move from the original scene to the sensor capture to the final RGB photo. Too much tonal compression makes an image look flat and or creates noise. Discarded tonal information leaves areas without detail.

    What highlight tone priority can't do is increase the total tonal capacity of an 8 bit RGB photo. That's a fixed target. That makes this a zero sum game. If the camera's image processor is expanding the space allotted to highlight tonality and insuring that the highlights are held at the top end of the histogram then this must be done at the expense of the rest of the photo's tonal data.

    This nonetheless can be a useful feature. Wedding photographers are repeatedly forced to photograph women in bright white gowns under uncontrolled lighting conditions. The bride doesn't want to hear some "photo-jargon" excuse about lighting and why her dress didn't come out in the photo. This is action photography during which little time is available to set up fill lights etc. etc. I'd use a camera feature like this under that circumstance -- pragmatism pay bills, but understand what you're doing.

    If I have the time to make a photo and think about it and control the conditions, then I will always out-perform the algorithms in the camera's processor. The best place to start is by controlling the lighting.

    Take Care,
    Joe
     
  4. Hardrock

    Hardrock TPF Noob!

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    Thanks guys! So basically it does what Big Mike stated (expose to the right). I probally need to go home and play with that feature but just wanted to hear from others and what they thought.
     
  5. clanthar

    clanthar TPF Noob!

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    Not exactly -- exposing to the right will give you a different result. The idea in both cases is to make sure and not blow the highlights as this is the worst exposure mistake you can make. Highlight Tone Priority goes a step further and processes the image with a set of software algorithms that bias the result toward preserving highlight detail. These algorithms also process the rest of the recorded exposure. Exposing to the right doesn't apply special processing.

    Take Care,
    Joe
     
  6. Inst

    Inst TPF Noob!

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    You're thinking of auto-lighting optimizer; Highlight Tone Priority is a feature which causes the camera to expose at 1-stop ISO below the nominal ISO, then use hardware to boost signal up to be equivalent to the nominal ISO. This is why you can't access ISO 100 or 50.

    The net effect is expanded dynamic range in the highlights at the cost of increased noise in the shadows. I'm personally wondering about whether you get increased highlight tone quality, however.
     
  7. clanthar

    clanthar TPF Noob!

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    Nope -- highlight tone priority (HTP) is what we're talking about. I've seen that comment on the internet; that HTP causes the camera to expose 1 stop below the ISO set. It most certainly does not do that. In order to do that the camera would have to alter the exposure to the sensor and it does not.

    I just ran a test to verify. I set the camera to Tv and locked in a 1/400 sec. shutter speed. With HTP off the camera meter selected f/7.1 for the exposure. With HTP on the camera meter selected f/7.1 for the exposure. So HTP does not cause the camera to deliberately underexpose. What the camera is doing it's achieving via software in the Digic processor. This makes sense -- with a 14 bit capture depth the camera's software can process the data using different tone response targets, and this is what Canon says their doing.

    Take Care,
    Joe
     
  8. Hardrock

    Hardrock TPF Noob!

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    Thanks for the info I will give it a try tonight and see what I think.:thumbup:
     
  9. snappy7

    snappy7 TPF Noob!

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    Hi. I've played with this on my 550d and I can't say I've noticed any real diff. I do have it switched on tho and and it will lock in the ISO to max 6400. Without HTP it will allow the ISO will go all the way up to 12800
     
    Last edited: Sep 5, 2010

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