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histograms and DPP


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I felt like sharing something, iso asking. I hope it helps someone understand it just that small bit better. And if I got it wrong, I failed my exams :D Big deal, I can only learn.

 

Sometimes you read articles, books and all and it just doesn't click. Overload of information, too detailed or too technical. It happens to me all the time.

 

So here's a topic about exposure: should one digitally expose fo a histogram slap in the middle, to the left (under exposed) or to the right (over exposed) and can you correct things in DPP?

 

I read about the way the chip accumulates pixels and starts with the high lights. So if the highlights "start" halfway, you end up with less information than when it starts to the utmost right without clipping.

 

In PS or LR or whatever I can change, manipulate and correct within almost 2 stops, right? Almost. The end result is different. I tried, just because I was curious, because I am rather "fresh" on DPP skills and because I felt like doing it :).

 

I took one shot with the histogram to the left (under exposed) and one with the histogram to the right (over exposed). Both just so it clipped. Then Ioaded the pictures into LR2 and only:

- corrected so the clipping was just within bounds

- brought the either the low side up or the high side down so the maximum pixels where within high and low (full covering histogram from left to right)

- converted cold turkey to grey scale

- cropped a specific spot in the water io to show detailed DPP in both pictures

 

In short: I tried to do the simplest DPP to get a match.

 

Ahhhhh ... I'm going to make sure I shoot so the histogram is slightly right sided.

 

Now hit me with your comments. Wait, I'll hide behind my screen. OK, go!

 

Marco

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Histograms just represent in a fast way what the sensor has recorded(tonal range from black to white vs quantity (area) shown in the photo). You should try to avoid clipping at first. Next you should try to record data in the whole spectrum from pitch black to pure white, if that is possible... it's not possible all the times. In the pictures you show, you might want to underexpose a bit so that you can invest more in the shadowed areas where you get more data, rather than the bright sky. You got a lot of options...

If you get a pic with a histogram shifted to the blacks you might want to counter this using fast lenses and/or slower speeds... and vice versa

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There are some other considerations as well: the eye is logarithmic, seeing more detail in darker areas. The M8 mimics that with its compression. So it s vital, if you want to conserve the full tonal range, to conserve the highlights. In other words, for a full range the histogram should just touch the right. The shadows must look after themselves. This contradicts the requirement at higher ISO to generate enough signal in the lower range to prevent noise. So then you must blow the highlights and expose the darks correctly.

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There are some other considerations as well: the eye is logarithmic, seeing more detail in darker areas. The M8 mimics that with its compression. So it s vital, if you want to conserve the full tonal range, to conserve the highlights. In other words, for a full range the histogram should just touch the right. The shadows must look after themselves. This contradicts the requirement at higher ISO to generate enough signal in the lower range to prevent noise. So then you must blow the highlights and expose the darks correctly.

 

Jaap, this is exactly as I understand it. I just wanted to SEE the effect, as sometimes you get that feeling that perhaps you can "save" things in DPP ... not so.

 

My post was just a "yessss, I understand how it works" as my wife wasn't going to pat me on the shoulder about this insight :)

 

Marco

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There are some other considerations as well: the eye is logarithmic, seeing more detail in darker areas. The M8 mimics that with its compression. So it s vital, if you want to conserve the full tonal range, to conserve the highlights. In other words, for a full range the histogram should just touch the right. The shadows must look after themselves. This contradicts the requirement at higher ISO to generate enough signal in the lower range to prevent noise. So then you must blow the highlights and expose the darks correctly.

 

If he has a M8, he should avoid all that DPP. Thats why we pay the premium for its lenses.

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If he has a M8, he should avoid all that DPP. Thats why we pay the premium for its lenses.

 

With all due respect, but as I'm shooting in RAW (DNG) I'll always have to DPP. No use having an M8 and expensive lenses to let the camera software do that job internally without regard of what I want to achieve.

 

But as in life, it's all a question of less is more.

 

Marco

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The trick is to use it less and less. I am certain that once you learn how the photocells in your M8 work and compose, or what to do for those high contrast frames, I am sure you will be able to forget lightroom at least 80-90% of the cases. I agree though sometimes its impossible to get rid of pp

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All these rules you follow looking your histogrames, talking always about the M8, must we apply when we use ISO 1250 and 2500? Which shape must present the histograme?

 

Thanks,

 

Francisco

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Forget about shapes. Shapes are formed because they show how much area a specific tonal point (say, light light gray of some %) occupies in your picture. So you don't care about shapes. ISO also follows very simple rules: you need to have it in the lowest possible setting, providing that you can cope with the speed chosen for a particular aperture you chose. If you feel fine with iso @ 2500, then use the auto ISO, set the upper limit, and how stable your hand is (speed) and off you go. If you want to test compensation, you can also use manual settings, and given the ISO and aperture you have chosen, play with the exposure meter, for left on spot and right led arrows(take 3 shots) or even play more.

 

Edit:

Im trying to find some good source for explaining histograms and I can't. Almost all present you with a greatly balanced photo/histogram, but you wont always be able to find that in your photos. For instance photos from a member (Etrusko) which are pitch black and very nice, will be regarded as mistakes if we follow what these sites suggest lol :p

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The trick is to use it less and less. I am certain that once you learn how the photocells in your M8 work and compose, or what to do for those high contrast frames, I am sure you will be able to forget lightroom at least 80-90% of the cases. I agree though sometimes its impossible to get rid of pp

 

It took some time to get to understand each other, but now we are exactly on par :D . That was my point in the first place: get your histogram right (understand how the sensor works et al)! No DPP can compensate for that, as can be seen in the example pictures.

 

In other words: as a student photographer I wanted to see for my self in practice how it worked.

 

By the way: I really love the way some of us work with DPP to get more out of a DNG. It all adds to the fun of being "around photography". Some will work towards 100% perfection straight out of camera, others will want to work in the post process. I learn from both and see the value of both.

 

Marco

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All these rules you follow looking your histogrames, talking always about the M8, must we apply when we use ISO 1250 and 2500? Which shape must present the histograme? Thanks, Francisco

 

Francisco,

 

Diogenes is right, as regular "bell shapes" don't come often in real life. This post is not about the shape, but basically about how to expose in order to get the most information on your sensor.You cannot compensate 100% by post processing. In other words: although programs like Lightroom let you shift exposure up and down 2 stops, the end result is not half as good as starting with the right exposure in the first place. And the way a sensor picks up light, it's (mostly) better to expose so the high lights just stay out of clipping.

 

There are lots of articles about histograms, but Understanding Digital Camera Histograms: Tones and Contrast is rather readable, I think.

 

Marco

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While I'm still looking for some decent explanation of histograms, let me add a couple more thoughts:

 

First of all you must understand what exactly they represent:

Understanding Histograms

This is what I liked the most from their definition:<<As mentioned earlier, with the exception of a histogram that is very heavily bunched up to the right (overexposed) there really isn’t such a thing as a “bad” histogram, or for that matter a “good” one. The histogram simply shows you the way things are, and its then up to you to decide if what it is telling you needs to be acted upon. Here are some examples.>>

 

In fact they showcase some nice examples which I also like, rather than the usual sterilized center weighted graphs which you will hardly ever find in normal shooting :p

Especially with the M8 and it's ability to shoot with no flash, histograms represent simply what things are. All that you really need to watch out is (as much as this is possible) not to record pitch blacks or blown whites.

Once you have accomplished this, then dpp should be kept at a minimum (at my opinion) simply because this is what the original scene is. So, unless you want to turn might into day in that moon photo, you don't need too much dpp work.

On the other hand, here is a photo with heavy dpp and more http://www.l-camera-forum.com/leica-forum/leica-m8-forum/68056-grand-prize-me-my-m8.html which deserved the prize it got...

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Marco and Diogenis,

 

Thank you for your comments. I've always the same problem when I try to participate in this Forum: unfortunately my English is very poor and many times I don't succeed in telling what I want to tell.

 

I've said "shape" and what I wanted to ask was: to have the minimum noise when I use 1250 and 2500 Iso must I go to the whites or better to the blacks? I've read some comments in the Forum and the opinions are not too much conclusive.

 

I beg you pardon for my delay :( and thank you again.

 

Francisco

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I am no expert on this subject, but one aspect seems to have been overlooked. The histogram on the camera display is surely a representation of that data which refers to a jpeg conversion, not the full information stored in a raw file. (Your later raw conversion should contain even more information.) I have been advised to regard the camera histogram merely as a guide to correct exposure and in that restricted sense, it is very useful.

 

I agree with the advice to avoid clipping the highlights in normal lighting conditions.

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to have the minimum noise when I use 1250 and 2500 Iso must I go to the whites or better to the blacks?

 

For a "theoretical", perfect camera, it wouldn't make any difference. For a real M8, which level compresses very heavily in the blacks, you'd be better off going to the right, into the whites, where more level resolution is available. However, I would not bias the mid tones off by more than 1-2 stops, depending on which raw converter you use; reason being that most raw converters apply a default tone curve that can make it very difficult to recover mid tones that are significantly off.

 

Sandy

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I am no expert on this subject, but one aspect seems to have been overlooked. The histogram on the camera display is surely a representation of that data which refers to a jpeg conversion, not the full information stored in a raw file. (Your later raw conversion should contain even more information.) I have been advised to regard the camera histogram merely as a guide to correct exposure and in that restricted sense, it is very useful.

 

I agree with the advice to avoid clipping the highlights in normal lighting conditions.

 

Where does the jpeg conversion routines enters the histograms?

I thought histograms are direct representations after reading sensor signals.

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For a "theoretical", perfect camera, it wouldn't make any difference. For a real M8, which level compresses very heavily in the blacks, you'd be better off going to the right, into the whites, where more level resolution is available. However, I would not bias the mid tones off by more than 1-2 stops, depending on which raw converter you use; reason being that most raw converters apply a default tone curve that can make it very difficult to recover mid tones that are significantly off.

 

Sandy

 

Sandy, when you say curves, you refer to the LUT?

I would say that using 1250 or 2500 ISO means more gain, and that introduces noise no matter what. What Sandy says applies to the whole range of ISO.

Personally I follow a different approach: according to where I want to invest: blacks or whites I shift my exposure right or left, assuming the frame is "difficult" or very contrasty or very dark or very bright. I correct for less than 1 -1.5 stops. But I am still a newbie with M8.

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