Hi all. I'm just starting to try and get to grips with using the histogram and have been trying to find out as much as possible on the web. I understand the idea of avoiding clipping highlights / shadows and how the histogram can show this, and I realise there is no one shape a histogram should look like. I haven't yet picked up how to use the histogram to judge exposure. Histogram to the left means darker and vice versa. Bright scenes like snow should have a histogram to the right (so I should use exposure compensation to over expose as camera metering will try to expose it like it is grey) and vice versa again. That sums up what I know so far. Firstly, am I on the right lines so far? Secondly, when you take a photo and look at the histogram, other than checking for clipping, what do you look for? I can never decide what I think it should show. Thanks everyone for your time
Histogram help
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tdodd
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You certainly are on the right lines. Really the shape of the histogram is quite unimportant. It is what it is and you can't change it except by recomposing your scene. What is important is where it is positioned between the left and right hand edges.
If it touches the right hand edge that is OK. If it climbs up the right hand edge then that indicates clipped highlights. Some clipped highlights might actually be perfectly OK, if they're not important. e.g. they might be small areas of brightness like reflections of the sun, street lamp bulbs at night or a backlit sky which you plan to crop out later. What the histogram won't show you is which parts of the photo are clipped. If you enable highlight alerts (Canon speak) then the blown areas will blink black/white when you review the image on the back of the camera.
As for the left hand edge, again, touching the edge is OK, but if the histogram is climbing up the edge it means you are losing details in the shadows, where the image appears as featureless black.
Sometimes the dynamic range of the scene is so great that you will get peaks climbing at both edges. Maybe there are steps you can take to reduce contrast, such as adding flash to brighten the shadows, or change your shooting location, direction, time of day or weather. If you can't change the dynamic range then consider which areas are of more interest - highlights or shadows - and tweak your exposure to save the important bits. e.g. you might be shooting a bride and groom in the sunshine. Her dress will be dazzling and his suit will be pretty dark in the shadow areas. The bride's dress is all important. The groom's suit..... not so much. Expose for the highlights. Develop (edit) for the shadows.
If the dynamic range of the scene is small and the histogram fits comfortably within the boundaries with space to spare then you might consider brightening the exposure in order to shift the histogram towards the right. This is a technique known as "Expose To The Right" and it serves to reduce noise and increase tonal detail captured. It's a technique I use quite often. There is no need to go mad and get it way over to the right. Just try to make your exposure a little brighter rather than a little dimmer, or simply shoot them to be spot on from the outset. If you shoot dark and then brighten in post you will see more noise and potentially posterisation as the tonal range gets stretched.
Shooting raw and using ETTR is a great way to squeeze the maximum performance from your camera.
By the way, I wouldn't describe adding +ve EC for a snow scene as "overexposing". I'd call it setting the exposure correctly in order to avoid what would otherwise by an underexposed image. A centred meter needle, or EC at 0 does not automatically mean a correct exposure. It just means that whatever you are metering is about equal to middle grey. If the thing you are metering is brighter than middle grey you need to add some EC. That, in my book, is not overexposing. It's exposing correctly.
If it touches the right hand edge that is OK. If it climbs up the right hand edge then that indicates clipped highlights. Some clipped highlights might actually be perfectly OK, if they're not important. e.g. they might be small areas of brightness like reflections of the sun, street lamp bulbs at night or a backlit sky which you plan to crop out later. What the histogram won't show you is which parts of the photo are clipped. If you enable highlight alerts (Canon speak) then the blown areas will blink black/white when you review the image on the back of the camera.
As for the left hand edge, again, touching the edge is OK, but if the histogram is climbing up the edge it means you are losing details in the shadows, where the image appears as featureless black.
Sometimes the dynamic range of the scene is so great that you will get peaks climbing at both edges. Maybe there are steps you can take to reduce contrast, such as adding flash to brighten the shadows, or change your shooting location, direction, time of day or weather. If you can't change the dynamic range then consider which areas are of more interest - highlights or shadows - and tweak your exposure to save the important bits. e.g. you might be shooting a bride and groom in the sunshine. Her dress will be dazzling and his suit will be pretty dark in the shadow areas. The bride's dress is all important. The groom's suit..... not so much. Expose for the highlights. Develop (edit) for the shadows.
If the dynamic range of the scene is small and the histogram fits comfortably within the boundaries with space to spare then you might consider brightening the exposure in order to shift the histogram towards the right. This is a technique known as "Expose To The Right" and it serves to reduce noise and increase tonal detail captured. It's a technique I use quite often. There is no need to go mad and get it way over to the right. Just try to make your exposure a little brighter rather than a little dimmer, or simply shoot them to be spot on from the outset. If you shoot dark and then brighten in post you will see more noise and potentially posterisation as the tonal range gets stretched.
Shooting raw and using ETTR is a great way to squeeze the maximum performance from your camera.
By the way, I wouldn't describe adding +ve EC for a snow scene as "overexposing". I'd call it setting the exposure correctly in order to avoid what would otherwise by an underexposed image. A centred meter needle, or EC at 0 does not automatically mean a correct exposure. It just means that whatever you are metering is about equal to middle grey. If the thing you are metering is brighter than middle grey you need to add some EC. That, in my book, is not overexposing. It's exposing correctly.
HoppyUK
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Yes, good OP Julian, you're on the way. And great post from Tim as always.
Don't get too bogged down on the detail of the histogram. I just break it down into three zones - highlights, mid-tones and shadows - and always have blinkies enabled (highlight alert, fantastically useful).
The key to it is knowing what a mid-tone is, and making sure it's in the middle. Mid-grey is 18% grey, or thereabouts. Best way I can describe it is elephant grey, and you'll often find that green grass is about the same, some tarmac is, brick walls, that kind of thing - all good references and ones that often take up a decent area of the image resulting in a larger and therefore more easily identifiable bump in the histogram. If you can identify the mid-tones in the image and tie them up with a bump in the middle, you're sorted. That is the basis of technically 'correct' exposure and if you output as a JPEG straight from the camera, it will be exactly right.
However, once you've nailed those mid-tones (and providing you're post processing and preferably shooting Raw*) you can then start to juggle things about and use ETTR technique, or know how to handle situations that don't have nice big areas of mid-tone, or with extremes of dynamic range.
That's when you need to look at the ends of the histogram - maybe move them left/right with deliberate under/over-exposure, fit a graduated filter, add a dash of fill-in flash, consider HDR technique. But it all starts with knowing where the mid-tones in the subject are, pinning them to the middle of the histogram, and then making either technical or creative decisions to change things around and get the result you want.
*In exposure terms, the biggest difference with JPEG vs Raw is the in-camera JPEG will chop off about one stop of highlight detail right at the top. Learn your camera, do some tests and find out just how much Raw highlight room you've got at the top. Note that picture styles affect both the histogram and blinkies, particularly the contrast setting - turn contrast down to get closer to what's actually on the Raw.
Don't get too bogged down on the detail of the histogram. I just break it down into three zones - highlights, mid-tones and shadows - and always have blinkies enabled (highlight alert, fantastically useful).
The key to it is knowing what a mid-tone is, and making sure it's in the middle. Mid-grey is 18% grey, or thereabouts. Best way I can describe it is elephant grey, and you'll often find that green grass is about the same, some tarmac is, brick walls, that kind of thing - all good references and ones that often take up a decent area of the image resulting in a larger and therefore more easily identifiable bump in the histogram. If you can identify the mid-tones in the image and tie them up with a bump in the middle, you're sorted. That is the basis of technically 'correct' exposure and if you output as a JPEG straight from the camera, it will be exactly right.
However, once you've nailed those mid-tones (and providing you're post processing and preferably shooting Raw*) you can then start to juggle things about and use ETTR technique, or know how to handle situations that don't have nice big areas of mid-tone, or with extremes of dynamic range.
That's when you need to look at the ends of the histogram - maybe move them left/right with deliberate under/over-exposure, fit a graduated filter, add a dash of fill-in flash, consider HDR technique. But it all starts with knowing where the mid-tones in the subject are, pinning them to the middle of the histogram, and then making either technical or creative decisions to change things around and get the result you want.
*In exposure terms, the biggest difference with JPEG vs Raw is the in-camera JPEG will chop off about one stop of highlight detail right at the top. Learn your camera, do some tests and find out just how much Raw highlight room you've got at the top. Note that picture styles affect both the histogram and blinkies, particularly the contrast setting - turn contrast down to get closer to what's actually on the Raw.
ernesto
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Guessing everyone has seen this (3rd result on Google of 'Histogram') but bit more high level info on Histograms
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml
HoppyUK
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Cheers guys, you're welcome. While trying not to over-complicate things, here's a bit more.
I said above that the key to understanding the histogram is being able to tie the mid-tones in the scene with the mid-tones of the histogram. Which it is, and in an ideal world that's a great way of working.
But what if there are no mid-tones, or you need another reference? Well actually, while using mid-tones is a great reference and usually easiest, you can use any tone, so long as you know it's value and where it should sit on the histogram.
For example, another method is to use the palm of your hand. That is always a constant tone, usually about 1.3-1.5 stops brighter than mid-grey, so you can also use that. Take a spot meter reading off your palm (making sure it's in the same light as the subject) and then add 1.3 stops to the exposure reading. That will put it in the right place, and therefore all other tones will fall in line too.
Likewise, you can also meter off a white surface - t-shirt, paintwork, whitewashed wall, piece of white paper. That will typically be about three stops brighter than mid-grey, so add 3 stops and you're there - it will be reproduced close to the right-hand side of the histogram, where it should be.
tdodd
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Following on from Richard's last post, here is an example with no mid tones in the scene, but very obvious highlights which can be spot metered and an exposure set to keep the whites white by metering the brightest part(s) at +3 stops.
As you can see, the bird is also well lit by bright sunshine, which allows another option for setting exposure to be considered. This is the "Sunny 16 Rule". The rule states that for a brightly sunlit subject, with the aperture set to f/16, you set a shutter speed equal to 1/ISO. So, with ISO at 100 your shutter speed would be 1/100 and with ISO at 400 your shutter speed would be 1/400 and so on. You don't need to shoot at f/16, and in this example I opened up the aperture by 2 stops to f/8. While keeping ISO at 100 I increased the shutter speed by 2 stops to 1/400 to compensate, thus maintaining an exposure equal to a "Sunny 16" exposure.
Now in truth, as this photo is getting on a bit, I don't remember whether I set exposure by metering from the highlights or by manually setting a Sunny 16 exposure to begin with. It could have been either technique, as the end result is the same. What I am certain of is that I would have checked the histogram and looked for blinkies to make sure my exposure was good before moving off to shoot something else.
This photo does need a WB adjustment and a bit of a crop, but as far as the exposure goes I'm very happy with it.
As you can see, the bird is also well lit by bright sunshine, which allows another option for setting exposure to be considered. This is the "Sunny 16 Rule". The rule states that for a brightly sunlit subject, with the aperture set to f/16, you set a shutter speed equal to 1/ISO. So, with ISO at 100 your shutter speed would be 1/100 and with ISO at 400 your shutter speed would be 1/400 and so on. You don't need to shoot at f/16, and in this example I opened up the aperture by 2 stops to f/8. While keeping ISO at 100 I increased the shutter speed by 2 stops to 1/400 to compensate, thus maintaining an exposure equal to a "Sunny 16" exposure.
Now in truth, as this photo is getting on a bit, I don't remember whether I set exposure by metering from the highlights or by manually setting a Sunny 16 exposure to begin with. It could have been either technique, as the end result is the same. What I am certain of is that I would have checked the histogram and looked for blinkies to make sure my exposure was good before moving off to shoot something else.
This photo does need a WB adjustment and a bit of a crop, but as far as the exposure goes I'm very happy with it.