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deliberate1

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Histogram question
« on: June 13, 2018, 01:53:58 PM »

I use the histogram to determine if all the available data that I want in an image has been captured. And I know that in an image containing highlights and shadows, the "goal" is a representation of tonality that spans no lower than 0 and no higher than 255, subject to aesthetics.
My question has to do with images that have very little, if any, contrast; where the histogram "curve" is very condensed and narrow on the horizontal axis. In such a situation, should I add exposure to move the entire "curve" to the right, and as close to 255 as possible, or just the opposite, and to the left. I guess what I am asking is whether images with very little tonal range should be exposed to the left right or center for the purpose of post processing. Or, as may be the case, it matters not at all.
Thanks.
David
« Last Edit: June 13, 2018, 02:00:39 PM by deliberate1 »
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digitaldog

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Re: Histogram question
« Reply #1 on: June 13, 2018, 02:33:29 PM »

First, I don't know what you mean by "Histogram Curve", can you explain.
Next, exposure only takes place at capture, an attribute of shutter and F-stop; the amount of light striking a sponsor (or film). You want to alter brightness I suspect.
Maybe this will help?



Everything you thought you wanted to know about Histograms

Another exhaustive 40 minute video examining:

What are histograms. In Photoshop, ACR, Lightroom.
Histograms: clipping color and tones, color spaces and color gamut.
Histogram and Photoshop’s Level’s command.
Histograms don’t tell us our images are good (examples).
Misconceptions about histograms. How they lie.
Histograms and Expose To The Right (ETTR).
Are histograms useful and if so, how?

Low rez (YouTube): http://www.youtube.com/watch?v=EjPsP4HhHhE
High rez: http://digitaldog.net/files/Histogram_Video.mov
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Andrew Rodney
Author “Color Management for Photographers"

deliberate1

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Re: Histogram question
« Reply #2 on: June 13, 2018, 03:01:39 PM »

Andy, forgive my terminology for its inaccuracy. The "curve" I am referring to is the vertical bars representing the tonality of an image, as if capped by a line. In the scenario I am describing, the bars are condensed and fall in a narrow range  - say between 0 and 50, or 50 and 100, or 100 and 150, etc. My question has to do with the best distribution along the horizontal axis for the purpose of post processing - ETTR or ETTL or whatever.
Thanks.
David
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nirpat89

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Re: Histogram question
« Reply #3 on: June 13, 2018, 03:31:11 PM »

I use the histogram to determine if all the available data that I want in an image has been captured. And I know that in an image containing highlights and shadows, the "goal" is a representation of tonality that spans no lower than 0 and no higher than 255, subject to aesthetics.
My question has to do with images that have very little, if any, contrast; where the histogram "curve" is very condensed and narrow on the horizontal axis. In such a situation, should I add exposure to move the entire "curve" to the right, and as close to 255 as possible, or just the opposite, and to the left. I guess what I am asking is whether images with very little tonal range should be exposed to the left right or center for the purpose of post processing. Or, as may be the case, it matters not at all.
Thanks.
David

There was a great long discussion on ETTR here not too long ago.  You might want to start there (check just a few threads down.)  Personally I do over-expose to move the right-most pixels to towards the 255 limit, but safely within (making sure I look at all three R, G, and B channels.)  The histogram is based on JPEG and not RAW so there is more lee-way than what you see on the back of the camera.  The shadows will be in essence exposed at much lower ISO which would reduce the noise, increasing the S/N ratio.  That is the main benefit.  Of course, the histogram has to be moved back in post to compensate. 

:Niranjan.
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digitaldog

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Re: Histogram question
« Reply #4 on: June 13, 2018, 03:33:59 PM »

Important: ETTR isn't over exposure! Over exposure is over exposure. ETTR (bad name) is ideal exposure for raw data. For that data.


https://luminous-landscape.com/the-optimum-digital-exposure/
http://digitaldog.net/files/ExposeForRaw.pdf
https://photographylife.com/how-to-use-the-full-dynamic-range-of-your-camera
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Andrew Rodney
Author “Color Management for Photographers"

Telecaster

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Re: Histogram question
« Reply #5 on: June 13, 2018, 03:38:06 PM »

With proper linear capture you'll want to push the histogram as far to the right as possible without clipping desirable highlight data. This assumes finest possible tonal gradation is what you're going for…and that the camera is actually writing linear data to storage (rather than, say, introducing a film-ish compression curve to individual photosite values above a certain threshold).

In practice when I see a histogram with blank space at both ends I'll kick up the exposure by 2/3-to-1 stop and call it done.

-Dave-
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nirpat89

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Re: Histogram question
« Reply #6 on: June 13, 2018, 03:45:50 PM »

Important: ETTR isn't over exposure! Over exposure is over exposure. ETTR (bad name) is ideal exposure for raw data. For that data.


https://luminous-landscape.com/the-optimum-digital-exposure/
http://digitaldog.net/files/ExposeForRaw.pdf
https://photographylife.com/how-to-use-the-full-dynamic-range-of-your-camera

What I meant by "over-exposure" is that I have to add +1 or +2 etc worth of exposure compensation over what is recommended by camera's auto-exposure mode.  As long as the highlights are not clipped, I guess, technically it is not "over-exposed."

:Niranjan.
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digitaldog

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Re: Histogram question
« Reply #7 on: June 13, 2018, 03:51:47 PM »

What I meant by "over-exposure" is that I have to add +1 or +2 etc worth of exposure compensation over what is recommended by camera's auto-exposure mode.  As long as the highlights are not clipped, I guess, technically it is not "over-exposed."

:Niranjan.
Exactly. It's more exposure and again, when conducted only with the camera. IOW, more exposure isn't necessarily over exposure, exposure cannot occur after capture. The camera Histogram is a lie and can be fooled to provide what appears as clipping which could (could) be not due to exposure but due to the color space used for representation of this Histogram. It's why we really need a raw Histogram on the camera. Short of that, there's RawDigger!
Another reason why raw+JPEG shooters are targeting optimal exposure for one kind of data, while not for the other.
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Andrew Rodney
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Guillermo Luijk

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Re: Histogram question
« Reply #8 on: June 13, 2018, 04:03:28 PM »

Hi David, visibe noise gets reduced the closer your RAW data gets to saturation, so yes, if you want to maximize your capture quality expose as much as you can before starting to clip your RAW file. Moreover a low contrast scene like the ones you are referring to can be a two edged sword: it's easy to capture, but they can be demanding in processing as well. If you are a 0..255 histogram lover (like Ansel Adams was), you'll insist in spreading the final image histogram by applying a strong contrast curve. This curve means your SNR will reduce dramatically, so the higher SNR you begin with, the better.

Regards

PS: Andrew, since when you switched your nickname from digitaldog? I loved that one :)

nirpat89

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Re: Histogram question
« Reply #9 on: June 13, 2018, 04:50:02 PM »

Exactly. It's more exposure and again, when conducted only with the camera. IOW, more exposure isn't necessarily over exposure, exposure cannot occur after capture. The camera Histogram is a lie and can be fooled to provide what appears as clipping which could (could) be not due to exposure but due to the color space used for representation of this Histogram. It's why we really need a raw Histogram on the camera. Short of that, there's RawDigger!
Another reason why raw+JPEG shooters are targeting optimal exposure for one kind of data, while not for the other.

Someone should come out with a camera OS which people can then use to do all kinds of apps like raw histogram.   Of course, the camera companies have to buy in which in their shortsightedness won't.
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deliberate1

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Re: Histogram question
« Reply #10 on: June 13, 2018, 09:38:19 PM »

Gentlemen, I thank you all for your very helpful insights and advice.
I learned something to day.
David
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digitaldog

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Re: Histogram question
« Reply #11 on: June 13, 2018, 10:23:35 PM »

PS: Andrew, since when you switched your nickname from digitaldog? I loved that one :)
Fixed!  ;)
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Andrew Rodney
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