Beginner Histogram importance?

Thatchapthere

Thatchapthere

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Hey guys,

Have found the plethora of info on here valuable, which I've been applying/experimenting/failing/passing etc....Ta!

Though, with all the different variations of application, histogram has now entered into the conundrum!

Is this an important aspect, on top of everything else?
 
For a beginner it might not be worth delving too deep into the science of the histogram!

However, as a VERY brief introduction - it runs from left (shadows) to right (highlights) with mid-tones in the middle. An AVERAGE well-exposed shot will have a kind of 'mountain range' extending the whole width of the histogram.
A 'flat' shot will have a lot of empty space to the left and right (lack of depth in shadows and lack of brightness in highlights).
A dark shot will be bunched to the left.
A bright, high-key shot will be bunched to the right.
And that's the point really - histograms are only of use if you understand them properly; because only AVERAGE exposures will show the "ideal" spread. Shots that are deliberately high- or low-key will show a different pattern : one that's not necessarily "right" or "wrong" but wholly dependent on what you want to achieve.
 
It depends on your preferred type of photography, but it's especially important in the great outdoors on a sunny day. Pointing the camera around the scene will yield different light readings between sky and the ground/foreground, so you'd be looking to have readings at top and bottom within the histogram scale for a balanced exposure. If that isn't available, you can use a tripod to take photos exposed for foregound interest and background/sky interest, and then combine these in Lightrooom or whatever.
 
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The histogram can be very useful for sure, but in everyday shooting the most useful exposure aid is known as 'blinkies' that are linked to the histogram - the highlights over-exposure warning that flashes black/white over bright areas of the image on the LCD. Canon calls it Highlight Alert in the menus, Nikon just Highlights I think. Everyone calls them blinkies.

Blinkies flash over areas that are definitely over-exposed, beyond the dynamic range of the sensor, and also on areas that are on the brink of over-exposure. The problem is that when a subject is over-exposed, it will appear pure white and there's nothing you can do in post processing to pull it back - it's blown, gone for good. If you want to retain detail in those areas, then you have some options:
- reduce overall exposure, but run the risk of losing detail in shadow areas and/or increased noise
- darken the bright zone, such as an over-exposed sky, with a graduated filter
- shoot brackets, ie several frames at different exposure settings and combine them in post-processing
- brighten darker areas of the image to bring the range of tones closer together (within the dynamic range of the sensor) with fill-in flash for example
- or just let them blow, because they're not important.
 
The top and bottom ends of the histogram have a clear use in showing potential over or under exposure.

However I can't see "any practical use for the data in the middle of the histogram! " Does anybody 'use' it?
 
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Provided you use the histogram while considering the view in front of you, and what you want to achieve, then a histogram is very useful indeed.
However it is produced from the equivalent of the jpeg not the raw data. So it tends to understate the amount of headroom available to a raw shooter, who will always be abe to recover more highligt detail in processing.

Some cameras like csc's and those using live view show real time histograms before you shoot . This is perhaps more useful than on many Dslr's which only show a histogram of captured images.

Most cameras only show the luminance graph, which can give misleading results in strongly coloured scenes. Photoshop and other processing packages give the RGB graphs as well, which can be more useful by indicating over saturated colours that are clipped.

Histograms are very useful indeed if properly understood.
 
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HoppyUK said:
The histogram can be very useful for sure, but in everyday shooting the most useful exposure aid is known as 'blinkies' that are linked to the histogram - the highlights over-exposure warning that flashes black/white over bright areas of the image on the LCD. Canon calls it Highlight Alert in the menus, Nikon just Highlights I think. Everyone calls them blinkies.

Blinkies flash over areas that are definitely over-exposed, beyond the dynamic range of the sensor, and also on areas that are on the brink of over-exposure. The problem is that when a subject is over-exposed, it will appear pure white and there's nothing you can do in post processing to pull it back - it's blown, gone for good. If you want to retain detail in those areas, then you have some options:
- reduce overall exposure, but run the risk of losing detail in shadow areas and/or increased noise
- darken the bright zone, such as an over-exposed sky, with a graduated filter
- shoot brackets, ie several frames at different exposure settings and combine them in post-processing
- brighten darker areas of the image to bring the range of tones closer together (within the dynamic range of the sensor) with fill-in flash for example
- or just let them blow, because they're not important.
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Exactly this :agree: :)

That saved me some typing lol

The Histogram may tell you something is blown but not where or how much, where & how much is what matters - gotta love Blinkies for this :)

The Histogram is like asking a man with no fingers for directions... pointless :D

Dave
 
ianp5a said:
The top and bottom ends of the histogram have a clear use in showing potential over or under exposure.

However I can't see "any practical use for the data in the middle of the histogram! " Does anybody 'use' it?
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Ok, here is what I have read, and I'm well prepared to be corrected.

The Histogram is a measure of how the tones are spread out in an image, from black on the left to white on the right, so far so good. I read this a few years ago from Adobe about Linear Gamma, and it influences how I use the Histogram. It says roughly that half the tones in your Histogram are in the fifth section of the Histogram on the right, and each section has half the remaining number of tones. Now in that link he talks of a camera with six stops of dynamic range, and most DSLR/CSC cameras have more than that now. But for a Jpeg image this could be, from left to right, 4,8,16,32,64,128, and for a 12bit RAW file 64,128,256,512,1024,2048. If you have lot of the tones in your image clumped on the left, and you end up having to brighten the image when post processing, then you run the risk of introducing noise as you spread out the limited number of tones in the darker areas. I think this is where the practice of expose to the right (ETTR) came from. If you can increase the exposure to move the Histogram over to the right, without over exposing anything important, then you should have more data to work with, and if you have to darken an image in PP then you should be reducing any noise present.

Now that was a few years ago I read about Linear Gamma, and the article is from 2004, and the sensors now seem to have amazing possibilities of shadow recovery, so I don't now whether the above was/is right, and if it was, whether it is still relevant with modern sensors. Please put me straight. :)
 
I still don't see any practical use for the distribution in the middle of the histogram. Just the top and bottom ends.

If I have chosen to meter for a particular tone, what use is it to know how much of my frame is filled with any particular tone? I am already see what the image looks like.

It might be better to display the 2 ends of the histogram enlarged and cut out the middle bit.
 
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ST4 said:
Histograms are vital.
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In what way ???

Vital is quite a strong word for something I have but never use, so we obviously do things completely differently

Oh, and I don't think you always need to avoid blinkies at all, you just need to know where they are, how much they affect the image, and then decide if its an issue or not taking action appropriately

Dave
 
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redhed17 said:
It says roughly that half the tones in your Histogram are in the fifth section of the Histogram on the right, and each section has half the remaining number of tones.
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This is the basis of ETTR, and I think it is wrong.
While "exposure" and the histogram are logarithmic, "data" and "tones" are not. There is no more difference between 64 and 128 than there is between 1024 and 2048. They are both exactly one stop different, and they both have the same amount of "distance/tones" between them. As long as a pixel collects enough photons to differentiate it from the surrounding pixels it will have a different tonality.

What *does* matter is the sensor's color depth/tonality capabilities (rated in bits), and to a much lesser extent the file bit depth used.
 
I'm a fan of the histogram for landscape work. A quick question regards highlight clipping.....

Isn't the image on the back of the camera a JPG with reduced latitude for highlights and lowlights, when I am shooting in RAW.
A histogram may show that the bright areas are in check, but on the back of the camera, the 'blinkies' will show the area as blown.
When I get the image into lightroom, it shows that the highlights are not blown, and easily recoverable.
Its always confused me a bit.
 
ianp5a said:
The top and bottom ends of the histogram have a clear use in showing potential over or under exposure.

However I can't see "any practical use for the data in the middle of the histogram! " Does anybody 'use' it?
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I use the middle quite a lot for critical or difficult subjects. It's where mid-grey should be, and that's the standard reference tone for 'correct' exposure. With that in the middle, it sets a base line and I know where I am - and take it from there.
 
MattyW said:
Its always confused me a bit.
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You're not confused at all there bud, you're exactly right :)

Blinkies is a useful guide to what may be blown, a bit of blinkies and its pretty much certain to be recoverable, you just need to learn when blinkies means "Watch out, blown coming" as opposed you "You've fkd it mate" :D

But blinkines tells you where and over how large an area, I shoot a LOT of landscapes and find the Histogram of no use whatsoever

Dave
 
MattyW said:
I'm a fan of the histogram for landscape work. A quick question regards highlight clipping.....

Isn't the image on the back of the camera a JPG with reduced latitude for highlights and lowlights, when I am shooting in RAW.
A histogram may show that the bright areas are in check, but on the back of the camera, the 'blinkies' will show the area as blown.
When I get the image into lightroom, it shows that the highlights are not blown, and easily recoverable.
Its always confused me a bit.
Click to expand...

Both the histogram and blinkies are generated off a JPEG (with all in-camera settings applied). What you're seeing is the effect of JPEG compression that simply chops a stop or more off the highlights end - it's the biggest single reason for shooting Raw IMHO.

The thing to do is a few experiments (because all cameras and processing regimes are slightly different) and get to know exactly how much headroom you have on the Raw file, after the point at which blinkies just start to flash. The in-camera Contrast setting affects this slightly - turn it down. For critical stuff, check the blinkies and then take another shot with say 1/3rd stop less exposure - if they go away, you'll then know pretty accurately where things are.
 
HoppyUK said:
I use the middle quite a lot for critical or difficult subjects. It's where mid-grey should be, and that's the standard reference tone for 'correct' exposure. With that in the middle, it sets a base line and I know where I am - and take it from there.
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If I understand you, you put the halfway point of the pixel data, bang in the middle of the histogram scale?
 
ianp5a said:
If I understand you, you put the halfway point of the pixel data, bang in the middle of the histogram scale?
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The objective is to make sure that a known tone in the subject appears in its correct position on the histogram. It could be any tone you like, in theory, so long as it's in its correct place, but mid-grey is easy as that should be bang in the middle and you can use a grey test card, or substitute natural subjects such as green grass, some shades of concrete or tarmac or brickwork etc.

That will give you technically correct exposure and you can just leave it there, and that's probably best if you're shooting JPEGs, or if shooting Raw and post-processing, then use it as a baseline reference for whatever further adjustments you want to make.
 
So when you hold up the grey card you see which part of the histogram reacts. Then adjust your exposure to put that 'spike' in the middle.
 
ianp5a said:
So when you hold up the grey card you see which part of the histogram reacts. Then adjust your exposure to put that 'spike' in the middle.
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All TTL meters take 'reflected light' readings. If you fill the frame with a subject that is an even tone all over - any tone, black white or grey - in any auto mode the camera will always set exposure so that the spike (or steep hump) of the histogram sits in the middle, regardless of the actual tone. This is the problem with reflected light readings, and the camera is dumb.

So the trick is to use a reference tone, ie grey card that your know should be in the middle. Then you now where you are.

Note that not all grey cards are mid-grey. Some are sold purely for white balancing, and are neutral grey, but not necessarily the 18% or 12% mid-grey needed for this purpose.
 
DG Phototraining said:
In what way ???

Vital is quite a strong word for something I have but never use, so we obviously do things completely differently

Oh, and I don't think you always need to avoid blinkies at all, you just need to know where they are, how much they affect the image, and then decide if its an issue or not taking action appropriately

Dave
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So if the sun is in the frame I'm free to allow blinkies then?
 
You are allowed them (don't make a habit of it)
While histograms aren't vital I think its rather odd to say they are of no use at all. Increasing the exposure does lessen the signal to noise ratio and when you adjust in ps you will get much better shadow detail. Digital cameras can now take lots of highlight detail and recover them very well so while `blinkies` are useful you will be able to recover them. If you shoot one over then bring it back in cr you will get the same histogram but much `better` detail in the shadows.
 
ianp5a said:
The top and bottom ends of the histogram have a clear use in showing potential over or under exposure.

However I can't see "any practical use for the data in the middle of the histogram! " Does anybody 'use' it?
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I can't see that you can have the 'ends' without having the middle part! ERGO - it must be important :p
 
chuckles said:
I can't see that you can have the 'ends' without having the middle part! ERGO - it must be important :p
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Most suggestions here are about over and under exposure. Where the top and bottom of the histogram can be used. The middle doesn't help there. If the ends are the most useful, they could be magnified. Which is similar to using the blinkies. So having a histogram doesn't seem that useful if you have blinkies. Especially if you don't have a grey card. And even if you do have a grey card, your meter will put that in the middle.
 
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ianp5a said:
Ok. Highlight and shadow. Right and left is just one convention.
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It is a horizontal graph, of which you say the only importance is clipping of blacks and whites, and that is left and right. :thinking: I only point it out so that we all are talking about the same things, given that this is a thread about understanding the Histogram. ;)
 
redhed17 said:
It is a horizontal graph, of which you say the only importance is clipping of blacks and whites, and that is left and right. :thinking: I only point it out so that we all are talking about the same things, given that this is a thread about understanding the Histogram. ;)
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I used top and bottom to refer to the high and low values. Which is valid whichever way the histogram runs. Horizontal or otherwise.
 
DG Phototraining said:
If that's what you want then of course

Seeing as we're discussing histograms though I'm not sure what use this point is :D

Dave
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I think the point is that whilst the histogram and blinkies are useful, (not that the histogram is crucial), the grey matter behind the lens is the important ingredient.
 
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Phil V said:
I think the point is that whilst the histogram and blinkies are useful, (not that the histogram is crucial), the grey matter behind the lens is the important ingredient.
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Pink matey - its only grey once you're dead :D

But yes, knowing what you're doing is the most important bit

Dave
 
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