# ISO D+ function



## aleshaloginov (Jun 29, 2014)

The question is whether it's profitable to use the D+ function. Recently have found it in my 6D and they say that with this thing the dynamic range of lights is much better, though there can be some extra noise in shadows.

It's called highlight tone priority.

What do you think about it, how do you use it? Any idea.


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## wickidwombat (Jun 29, 2014)

I dont bother 
it effects jpg files only
generally it will under expose the shot


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## steliosk (Jun 29, 2014)

Highlight Tone Priority (HTP) increases a bit the dynamic range.
in a few words: it helps the overexposed areas in recovery also in RAW

The other one named "Auto lighting optimizer" actually increases the midtone curve in jpeg (useless in raw)

In order to check it out take a shot of a lamp or a candle, with HTP on and off and try to recover the highlights in RAW (i use adobe camera raw)
You'll find out that the color and the depth of information is richer with the one that HTP is on.

Now the bad news:
Although canon has reached high ISOs where you can shoot in low light it hasn't been able for ages to fix the noise in low ISOs. (wondering why nobody is screaming about it, except me)

When you enable the HTP the minimum ISO you get is 200
and yes its NOISY as hell in the shadows. it sure ain't as clean as 100.

So i don't recommend HTP when shooting landscape. Get a tripod and use bracketing and merge them somehow after in post process or do HDR.

But if you are a handheld shooter and you need your camera to suck all the dynamic range there is, i suggest you turn HTP on and kill the noise with some noise reduction.


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## wickidwombat (Jun 29, 2014)

im pretty sure it does sweet FA in raw but i might be wrong.
It just applies a different process to the raw file than it normally would
check the manual


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## steliosk (Jun 29, 2014)

Hi wickidwombat

I made the test
2 shots using same ISO (200), speed and f stop
one shot with D+ and another one without
the one with D+ gave me better color results in the overexposed areas when lowering the highlights in ACR


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## wickidwombat (Jun 29, 2014)

steliosk said:


> Hi wickidwombat
> 
> I made the test
> 2 shots using same ISO (200), speed and f stop
> ...



like i said i might be wrong  

but part of the reason it only does iso 200 is the raw file manipulation
I think neuro will clear it up eventually, in any case i agree bracketing and using enfuse is a much much better solution


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## neuroanatomist (Jun 29, 2014)

steliosk said:


> I made the test
> 2 shots using same ISO (200), speed and f stop



Except they weren't the same ISO, because your camera lied. 




wickidwombat said:


> im pretty sure it does sweet FA in raw but i might be wrong.
> It just applies a different process to the raw file than it normally would
> check the manual



It's not so much that HTP affects the RAW data per se, but it does affect the RAW metadata in a way that's not handled properly by anything but DPP. 

What HTP does is deliberately underexpose by one stop, and 'misrecord' the ISO in the metadata - that's why ISO 100 isn't available when you turn on HTP, i.e. you set ISO 200, it shoots at ISO 100 but records 200, or you set ISO 800, it shoots at 400 and records 800. If shooting JPG, it processes the underexposed image to brighten everything except the highlights (meaning it applies a tone curve). If shooting RAW, it sets a metadata flag so DPP can apply that tone curve. 

If you open that RAW file in a 3rd party converter, results vary. Some ignore the flag and you just get an underexposed image. Others compensate by just boosting the total exposure by one stop - I think ACR (LR/CS) does that. Of course, that just re-blows your highlights and adds shadow noise. AFAIK, no 3rd party converter tries to replicate the tone curve to preserve highlights. 

So, if you shoot RAW and use a converter other than DPP, I'd leave HTP off so your reported ISO reflects the actual ISO used to take the shot, and just expose properly to preserve highlights. You can apply your own tone curve, not limited to the one full stop forced by HTP.


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## PhotographerJim (Jun 30, 2014)

neuroanatomist said:


> steliosk said:
> 
> 
> > I made the test
> ...



Thanks for the info Neuro, you always amaze me... 8)


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