# Photographic histograms



## spitfire (Feb 10, 2007)

I'd like to understand them and learn how to use them. Anyone know of any good tutorials?


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## Mini 360 (Jul 17, 2009)

Dont know of any but usually a good histogram is one that spikes in the middle and runs off equally on both sides to the very edge smoothly. If its biased to the left its underexposed, to the right overexposed. Hope that helps a bit. :thumb:


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## smalltrees (May 7, 2009)

*Histograms...*

the most confusing, and by far the most "eye catching" feature... to sell cameras... it is only added to sub-pro cameras to sell more...

first, there is "NO" correct histogram, that can be applied from one image to another, unless all the tones and lighting is exactly the same... even in a studio situation, each image can be very different...

Every perfectly exposed image, will have it's own unique histogram, and they will rarely every come close to matching...

an image of a black car, with black leather seats, will have a completely opposite looking histogram, as a white car shot in snow... all the data will be at opposite ends... and both histograms will look completely wrong, to "almost" all photographers, who think they understand histograms...

you can use them, to be sure, little if any data touches the top, or it will be overexposed... but, in almost any shooting situation, there "will" be something overexposed... called a specular highlights... they are good... the histogram calls them bad...

learn to use, trust your meter... far more accurate, than the displayed histogram, in the corner, on a 3" LCD...

judge composition with the LCD... do not use it as an exposure gauge... learn how to use the meter, and how it reads the scene... learn to read your scene, and how your camera's meter will see it...

bells and whistles and shiny flashing things sell cameras... while the lens and meters do all the work...

trust the lights, bars, arrows of your meter, learn how your meter works, to get the correct exposures... then, and only then, "after" you know the exposure "was" correct... should you look to admire the histogram...

9 out of 10 camera salesman, cannot "truthfully" explain a histogram... calling it a way to "accurately" judge exposure... is a pile of steaming BS...

histograms and curves are used in programs like Photoshop, to map the file's exposure, but, they will appear/act differently as to the histogram on your camera... and be far more accurate...


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## bretti_kivi (Apr 22, 2008)

I won't quote it. WHS.

However..... one thing I have found them halfway towards usable for is the setting of exposure when using high ISOs. I went out yesterday deliberately with ISO 500 - 800 set on the cam and the results are virtually indistinguishable from the ISO 100 shots I normally take. Why? because there's no struggle for light - a deliberate decision to expose towards the right-hand side of the histogram. Taking down without noise is easier than pushing it again. 

OTOH, what the histogram was telling me... errr, no. I got really annoyed with P again so shot what seemed to be right and I was within 2EV with 1 exception. RAW FTW 

Bret


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## spitfire (Feb 10, 2007)

smalltrees said:


> the most confusing, and by far the most "eye catching" feature... to sell cameras... it is only added to sub-pro cameras to sell more...
> 
> first, there is "NO" correct histogram, that can be applied from one image to another, unless all the tones and lighting is exactly the same... even in a studio situation, each image can be very different...
> 
> ...





bretti_kivi said:


> I won't quote it. WHS.
> 
> However..... one thing I have found them halfway towards usable for is the setting of exposure when using high ISOs. I went out yesterday deliberately with ISO 500 - 800 set on the cam and the results are virtually indistinguishable from the ISO 100 shots I normally take. Why? because there's no struggle for light - a deliberate decision to expose towards the right-hand side of the histogram. Taking down without noise is easier than pushing it again.
> 
> ...


My bad I should have mentioned that I'm looking to use them in post processing. I never had the thought of using them in-camera


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## bretti_kivi (Apr 22, 2008)

in PP.... why?

Moving curves for a more "equal" histogram won't necessarily help.










Download that, open it up. Look at the histogram. Is it really "spot on"? According to the printers, it is...

Seriously consider using the Histogram as a guide to adjusting curves and therefore levels, but it's a guide.

Bret


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## spitfire (Feb 10, 2007)

bretti_kivi said:


> in PP.... why?
> 
> Moving curves for a more "equal" histogram won't necessarily help.
> 
> ...


Ok, I'm starting to get the point. None of you seem to think Histograms are worth bothering with, but the thing is, I know nothing about them to say otherwise. I just wish to undersand them as with all other aspects of photography. It won't hurt to understand them and see if they are worth including in my work flow. Levels and curves really mean nothing to me when I look at them


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## bretti_kivi (Apr 22, 2008)

Now, *they* should mean something to you 

This lot was taken as screenshots (I thought I'd posted this already here?).... and ought to help with at least the beginning. These are using UFRaw (as it's free and works very nicely, thanks):










this is "auto" corrected and with the curve returned to standard.










So, if I start from there... well, it's too pale, and I'm not convinced on the Whitebalance (easy way to check - people's skin or sky.. it should look "normal"). 
So, WB set to "camera WB", then curve applied... 









I have a couple of other curves, too, you can see what they do:










and










Note that moving the bottom and top of the curve will also have an effect...


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## Mini 360 (Jul 17, 2009)

^^Thats helped me^^

Thought I knew a bit about Histograms but obviously not haha!


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## smalltrees (May 7, 2009)

*Histograms in Post-Processing...*

a Histogram is a "visual" representation of the tonal distribution of an image...

in the old days of film, you could expose a 21 step wedge onto film, develop then measure the densities, using a densitometer, and accurately produce a film curve... you could accurately measure one stop of exposure versus your development, to judge/correct/adjust contrast, or tone placement... 
ie The Zone System...

In the digital world, sensors cannot be measured in the same way, and each company's "secretive" algorithms, will produce the same scene with different sets of numbers... basically using software, instead of a densitometer, but, the software is all different, so there is no common ground...

film curves were difficult enough, to understand... for the average photographer... I worked for 25 years in photo-processing... I lived by film curves, to ensure quality processing and happy photographers...

Photoshop takes the digital data, and converts it, to what appears to be a "normal" film curve, so it is easier to "visually" understand your images... Histograms are similar to film curves, as they also show tone placement, color tone placement of your images...

I know photographers that "correct by numbers" balancing colors exactly by using the number values... this may make the image correct, numerically, but, it may not be the best visually... The color of sunlight changes during the day... correcting by the numbers, wants to make everything neutral...
neutral is good, but, may not be visually the best or accurate to your scene...

using histograms, can be helpful if you look at all three channels RGB, so you see the tone distribution of each color... it will help you learn and understand color better, or they more often confuse you even more... wink/smile...

you can quickly help an image using levels, going through each color, and moving the sliders to the ends of the detail, of each color... this may seem easy, but, depending on your image, where detail starts and stops can be difficult to see, unless you make your histogram full screen in size... think of a white bridal dress, or a white car... very difficult to see via a graph where that detail is...

It is always better to use your trained eye, to make corrections... and not rely on numbers... Photography is a visual medium, use your vision... you can learn to correct color using numbers, but, too many people stop there, assuming it is correct, and neglect to add their personal impression of the scene they saw when taking the photo... those people take snapshots, and do not create images... and there is nothing wrong with this... just missing the creative power...

Judge your image, by using, watching the image, not by using a graph or numbers...

Being from the printing world, I also know you can print, reproduce colors by simply mixing color, by using numbers, and know the end result will be correct... using the same set of numbers what I see in Seattle, will be the same as you see, your printer sees in your part of the world...

If... you are serious, you will know your environment is correct, your monitor is a quality monitor that is calibrated on a regular basis, so what you see, is correct, and what your printer sees, is also correct...

histograms, curves, are "only" visual aids to help you correct/adjust/improve/destroy your images...

CS4 has made it much easier to adjust any tone, by using the adjustments from a chosen point, using the little pointing finger button... Photoshop, in it's "own" way, having you visually correct, instead of relying on numbers/graphs...

I hope this helps...


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## bretti_kivi (Apr 22, 2008)

It's another tool in your armoury to make sure overexposure is not happening.

Good example of something I should have seen and dealt with while I was taking the shot:










Top left - it's washed out. You can see the edges... urgh. I should have either used a reflector, flash or something else to move the light around OR used 2-3 different exposures.

I'll try and find the original to show the histograms.

Bret


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## bretti_kivi (Apr 22, 2008)

found something else which is better for showing histograms....

let's start here:









You see the histogram is heavily pushed towards the right? That's because of all the pale snow.

Pushing the curve towards an S gives me a lot of contrast back and seems to level out the histogram.










Pushing the curve upwards is in this case very silly. Moving the bottom of the curve to the left will lighten dark sections, moving the top section down will reduce the maximum light used.










The final version below shows the effect of increasing the blackpoint, (i.e dark stuff goes black). It increases contrast, but you must use with caution.










This is what UFRaw thinks is the "optimal" histogram:










Curves can really help if you've not got enough light in the right place or screw up with a-bit-too-dark shadows.

HtH

Bret


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## spitfire (Feb 10, 2007)

Bret, Smalltrees, thanks for taking the time to try and explain this to me. I'm actually wondering now if it's worth the effort to try and learn all this curves and numbers game. Using NX2 Capture I create my images by simple moving sliders to acheive a result I'm happy with. Probably nowhere near perfect by numbers, but by using RAW and saving the result by JPEG I can end up with more than one final result.

For instance, the picture below was taken today as RAW. Ive resized it and converted to JPEG to post on here but no other processing has taken place.








The picture below is my result after editing. It was acheived by moving various sliders such as sharpening, saturation and contrast ect ect. Now it seems to me like your saying that if I use the Histograms then maybe I'm going to end up with a sterile version of the first pic. If that's the case I don't think I'll bother.​






Bret, yes I did see that post of yours before but I still have trouble understanding the mechanics of it, like where do you decide to put the points on the diagonal line before changing the curve.
Your screen shots are a bit different from my NX2 layout too.​
Thanks again to both of you for your help.:thumb:​


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## Top_Gun (Dec 7, 2009)

smalltrees said:


> Every perfectly exposed image, will have it's own unique histogram, and they will rarely every come close to matching...
> 
> an image of a black car, with black leather seats, will have a completely opposite looking histogram, as a white car shot in snow... all the data will be at opposite ends... and both histograms will look completely wrong, to "almost" all photographers, who think they understand histograms...
> 
> ...


Sorry, but I dare to differ. I use my camera quite a lot to shoot theatre, and the histogram is very helpful for critical lighting light brightly-lit people in front of black walls.

Since there is no "correct" exposure, a histogram is not able to indicate a correct exposure. However, there are often technically bad pictures which have blown highlights or too much "blackness" in dark areas, and a histogram is able to show this quite well. Having a look at my specialty, theatre: On a scene with dark background, you will want to avoid full exposure to the right, as those "highlights" will turn out to be whitewash in the actor's faces. The review of the picture on the display is usually not accurate enough to show this - if it is, you will often have to zoom in to find the blown highlights.

So, a histogram will definitely help me to find an acceptable exposure, meaning that I create pictures which I can later optimize and which contain the most details possible. You can always create some high-key effects in a picture with acceptable exposure, but you can't recover an actor's face or shirt which has been technically overexposed.

I will even go one step further: In tungsten light or really artificial lighting, a photographer will even benefit from a three-stage RGB histogram which will show overexposures which will occur only in the red channel.

Best regards,

Detlev

http://www.rackow-fotodesign.de/


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## bretti_kivi (Apr 22, 2008)

sich für eine Meinung entschuldigen muss nicht sein, denke ich 

Nicely explained.

Bret


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## smalltrees (May 7, 2009)

*We Differ less than you think...*



Top_Gun said:


> Sorry, but I dare to differ. I use my camera quite a lot to shoot theatre, and the histogram is very helpful for critical lighting light brightly-lit people in front of black walls.
> 
> Since there is no "correct" exposure, a histogram is not able to indicate a correct exposure. However, there are often technically bad pictures which have blown highlights or too much "blackness" in dark areas, and a histogram is able to show this quite well. Having a look at my specialty, theatre: On a scene with dark background, you will want to avoid full exposure to the right, as those "highlights" will turn out to be whitewash in the actor's faces. The review of the picture on the display is usually not accurate enough to show this - if it is, you will often have to zoom in to find the blown highlights.
> 
> ...


Detlev...

I think we differ much less than you think... Shooting in a theatre is the most challenging, and from your website, you do it very well... and obviously understand metering very well... it is the "classic" scene for using a spot meter, where you measure just the actor's face, and not allow the background, to sway the meter readings... most modern cameras have this feature, to allow spot metering...

There is always a "Correct" exposure... and then the exposure you choose...
yes, of course, in the theatre, there is no one exposure that will capture what your eye sees, we are able to see the brightly lit face of the actor, and also see into the shadows... cameras, film or sensors simply cannot see this range, you can expose for the shadows, and lose the actor, or expose for the actor, and lose the shadows... there is no exposure for both...

here are a couple good links, that shows different histograms, and just how different the correct exposures can appear, yet be correct histograms...

http://www.cambridgeincolour.com/tutorials/histograms1.htm

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

Histograms can show you areas being clipped during exposure... this is a good warning, but, it does not tell you what those areas are... 
someone's forehead, yes, this is vital detail and would be, very bad... 
a specular highlight from a chrome bumper, if this is not clipped, the image will be dull and lifeless, from being underexposed...

Yes... I am an old fart, so I learned to expose film by using a meter, and understand how a meter works... and how knowing your scene can effect the way your meter reads... and understanding what it tells you...

I have just seen too many salesmen, glowingly telling the customer how the histogram will give you perfect photos... 
bells and whistles and shiny things...

I only propose learning the scene you are shooting, by watching the scene... and not the back of your camera... wink/smile...


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## Top_Gun (Dec 7, 2009)

Thanks for the compliments. Using a "1" makes it easier, as it's possible to use spot metering coupled with the autofocus. The spot will not measure the centre like in the semi-pros, but will use the metering field overlapping with the chosen focus field. You calibrate just once, then it's just a matter of putting the focus on the face which is generally a good idea 

This feature does indeed compensate for the mediocre display of the 1D Mk3 - the display is large and bright, but the visual will often indicate an overexposure although all the details are perfectly preserved. I really need the histogram to compensate this problem.

However, I disgress. There are usually no faces on a car 

Best regards,

Detlev


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