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what is "auto lighting optimizer and highlight tone priority"?

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Thread started 16 May 2008 (Friday) 01:12   
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10-Dee-Q
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Okay so i have my 450D for about a month for now, and i took a lot of photos and has been very very satisfied with it .
but i do have some question cause i feel the supplied manual didn't explain this to well for newbie like me.

#1> What is "Auto Lightig Optimizer" ?

#2> What is "highlight Tone Priority" ?

and can you please tell me when i should turn them on or off ?

And one more , i knew that we used to cover the vf when taking picture in bulb mode so thus the metering will be more accurate, but how about when taking pics with the liveview ?
do we still need to cover the vf ?
cause from what i see the vf is not available when shooting in live view mode .

thx

Post #1, May 16, 2008 01:12:34


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basroil
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1) i will guess it's just a special code that normalizes light levels after exposure, only useful in JPG.
2) a fake iso setting that underexposes an image then uses software to bring the highlights down and shadows the same.

both will kill your already pathetic buffer. if you shoot raw, no need for either.

for last question, no, since exposure during live view is handled by "the sensor" itself rather than the exposure metering sensor.

Post #2, May 16, 2008 01:18:08


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10-Dee-Q
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basroil wrote in post #5534444external link
1) i will guess it's just a special code that normalizes light levels after exposure, only useful in JPG.
2) a fake iso setting that underexposes an image then uses software to bring the highlights down and shadows the same.

both will kill your already pathetic buffer. if you shoot raw, no need for either.

for last question, no, since exposure during live view is handled by "the sensor" itself rather than the exposure metering sensor.


okay so maojrity of people here turn it off ?

Post #3, May 16, 2008 01:49:26


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tzalman
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basroil wrote in post #5534444external link
2) a fake iso setting that underexposes an image then uses software to bring the highlights down and shadows the same.

both will kill your already pathetic buffer. if you shoot raw, no need for either.

Just for the sake of accuracy, it actually works the opposite: the highlights remain the same (with less exposure) and the shadows are boosted.

Since I shoot only RAW, I never use HTP, but for jpg shooters I think it might be quite useful if you are willing to except the reduction in continuous shot capacity (not everyone uses the camera like a machine gun) and are aware to the possibility of noise in the shadows if you are using a high ISO. Of course you can reduce exposure to prevent blowing out highlights and then adjust the shadows later in post-proccessing, but you risk posterization in the shadows (because jpgs are 8 bit) while HTP has the advantage of being done in 14 bit.

I am not familiar with "Auto Lighting Optimizer" (new with the 450D) but I suspect it might have the same 14 bit vs. 8 bit advantage.

Post #4, May 16, 2008 04:21:15


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apersson850
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First, highlight tone priority does not reduce the capacity for continuous shooting. You are mixing it up with the noise reduction for high ISO setting.

Then, wheteher you like to say that it reduces exposure of highlights and keeps the shadows the same, or the other way around, is mainly a semantic thing. The effect is at least that the dynamic range in the recorded image is reduced, compared to the subject you are shooting, which means it's possible to have the shadows and highlights at the same time, without blowing the highlights. As nothing is for free, the penalty is that the shadows have to be closer to the highlight, so you'll get slightly more noise in the shadows, due to the amplification.

The auto lighting optimizer was first introduced in the 40D. But there you can't turn it on or off. Instead, it works in the pre-programmed modes only, but there always. It's supposed to help you getting details everywhere in the image, by compressing the dynamic range in the subject. Boost shadows and reduce highlights.

I haven't seen the technical details explained, but as far as I've understood, highlight priority reduces exposure of highlights, but lighting optimizer attacks both the highlights and deep shadows.
It seems reasonable to expect a better result when doing this whilst working with 14 bits, not 8.

Post #5, May 16, 2008 05:22:08 as a reply to tzalman's post 1 hour earlier.


Anders

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Doug ­ Pardee
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10-Dee-Q wrote in post #5534430external link
What is "Auto Lightig Optimizer" ?

It's similar to having the camera do an "auto levels" adjustment on the image. This helps give the "ready to print" results that people have come to expect from digicams.

What is "highlight Tone Priority" ?

HTP exposes the image at one ISO level below the indicated ISO level, thus increasing the amount of highlight headroom in Raw by one stop. The in-camera JPEG conversion then corrects for this, using a curve that gently compresses the extra highlights. Canon Raw converters presumably can do the same kind of correction—most third-party Raw converters don't and merely show the Raw file as being one stop underexposed.

can you please tell me when i should turn them on or off ?

They're options because some people like them one way and some like them another. If you're shooting Raw, you probably will want to leave them both off. If you're shooting JPEG, then it depends on what settings give you the results that you like.

i knew that we used to cover the vf when taking picture in bulb mode so thus the metering will be more accurate, but how about when taking pics with the liveview ?
do we still need to cover the vf ?

No, you don't need to. The reason that you cover the viewfinder in Bulb mode is to prevent stray light coming in the viewfinder opening from fooling the metering sensors in the viewfinder. Those metering sensors are not used in Live View mode, and the mirrors are up and blocking any light coming in the viewfinder from reaching the main sensor.

Post #6, May 16, 2008 11:14:58




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apersson850
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One thing to remember is that if you are using Auto Lighting Optimizer, it doesn't combine with exposure compensation.
The software will see the result of the picture, after exposure compensation, as too dark or too light, and fix accordingly after the exposure, but before you can look at the jpeg image. So it will counteract what you set the camera to do.

Highligh tone priority I typically use in high-contrast situations, which usually happen in strong sunlight or the opposite, in darkness in city environments, where lamps are very bright compared to the rest of the scene.

Post #7, Sep 15, 2009 07:51:26 as a reply to Doug Pardee's post over 1 year earlier.


Anders

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Joaaso
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HTP is useful for raw-shooters as well, for those here who believe it only applies to jpg.. did a test myself last night to confirm it.. and it really starts to get interesting if you combine it with the "expose to the right" technique -gives you alot more room to play with...

Post #8, Sep 30, 2009 02:18:28


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Daniel ­ Browning
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Joaaso wrote in post #8732558external link
HTP is useful for raw-shooters as well, for those here who believe it only applies to jpg.. did a test myself last night to confirm it.. and it really starts to get interesting if you combine it with the "expose to the right" technique -gives you alot more room to play with...

You are mistaken. When in manual mode, HTP produces the *exact* same raw file as if you reduce the ISO by one stop. In AE mode (Av, Tv, P, etc.) , HTP produces the exact same raw file as if you reduce the ISO by one stop and decrease EC by one stop.

Post #9, Sep 30, 2009 02:35:12


Daniel

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Daniel ­ Browning
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Joaaso wrote in post #8732742external link
and the raw files i got then were not the exact same as the non-htp at all..

Keep in mind that many raw converters do not show you what the raw file is really like. For example, Adobe (ACR and lightroom) applies a hidden exposure compensation to hide the effect of HTP. In other words, you have to set -1 EC in Adobe to see what the raw file would have been like before it applied the secret adjustment. If you want to see what the raw file is really like, try Rawnalyze.

Post #10, Sep 30, 2009 04:14:54


Daniel

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Joaaso
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Daniel Browning wrote in post #8732759external link
you have to set -1 EC in Adobe to see what the raw file would have been like before it applied the secret adjustment.

that I did do, and noise-levels became pretty much the same, but still there was alot less blown out highlights than the non-htp shot, so I can't see how they could be the exact same..

Post #11, Sep 30, 2009 04:39:26


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Daniel ­ Browning
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Joaaso wrote in post #8732818external link
that I did do, and noise-levels became pretty much the same, but still there was alot less blown out highlights than the non-htp shot, so I can't see how they could be the exact same..

That could also be caused by Adobe's hidden highlight guessing ("recovery") algorithm. Most people think that the highlight guesser only applies when you use the "highlight recovery" slider, but Adobe also enables it when the exposure slider is used. (The exact rules and behavior is unknown to me.)

Post #12, Sep 30, 2009 04:47:08


Daniel

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Joaaso
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well i'm talking about blown highlights that are unrecoverable -my non-htp shot had some of it, the htp-shot didnt, when all other settings were the same.. even with 2 stop higher ISO, htp left me with less blown highlights in this particular scene.. and when that overexposure was counteradjusted in PP, the end result was alot less noisy than the non-htp shot..

Post #13, Sep 30, 2009 04:55:03


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Daniel ­ Browning
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Joaaso wrote in post #8732851external link
well i'm talking about blown highlights that are unrecoverable -my non-htp shot had some of it, the htp-shot didnt,

OK, that rules out the highlight guessing software.

Joaaso wrote in post #8732851external link
...when all other settings were the same.. even with 2 stop higher ISO, htp left me with less blown highlights in this particular scene..

Are you certain that f-number, shutter speed, and scene luminance (i.e. brightness of the subject you are photographing) were exactly the same? If a cloud passed in front of the sun or something, it it could cause one to have less blown highlights than the other.

If you post the raw files (such as after you redo the test) I'd like to take a look at them.

Post #14, Sep 30, 2009 05:05:26


Daniel

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Joaaso
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Daniel Browning wrote in post #8732879external link
OK, that rules out the highlight guessing software. Are you certain that f-number, shutter speed, and scene luminance (i.e. brightness of the subject you are photographing) were exactly the same? If a cloud passed in front of the sun or something, it it could cause one to have less blown highlights than the other.

If you post the raw files (such as after you redo the test) I'd like to take a look at them.

yeah i was in manual, and this was inside my apartment at night, so no change in light... i'll test some more, look at it in rawnalyze and post it later today..

Post #15, Sep 30, 2009 05:55:09


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