Reading The Histogram

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1 Reading The Histogram Here we explain the use of the Histogram, helping you to spot whether your photographs are under or over exposed. Task Take 3 photographs of the same thing, one at an EV of -2, one at 0 and the last at +2. See how different the histograms look on the preview in your camera. Nick Kind course@nickkind.com

2 Introduction Now we understand a bit more about Exposure Compensation and know how we can get the balance of light in a photograph better, we can begin to understand the Histogram Graph. This is a graphical representation of the light values of the image and can be one of the most useful features of a digital camera. The idea is by looking at this graph you can see whether your image is over or underexposed. This feature is usually available in the preview mode of your camera. Some cameras can see the graph in real time. Obviously all digital cameras have a preview screen which shows you your photographs and you can see if they are ok. However this can sometimes be wrong. The screen could be set brighter or the angle you are looking at the screen could be making a difference. But the most important thing, is the screen is showing you a large picture on a very small screen and when images are displayed smaller they can look a lot better / different than what they actually are. The Histogram does not lie!

3 The Histogram A typical Histogram is shown below. This is exactly the same graph we see when we look at Levels in Adobe Photoshop. The Histogram displays where all of the brightness levels in the photograph are found, from the darkest to the lightest. These are displayed along the bottom axis from 0 which is pure black to 255 which is pure white. The vertical axis shows the amount of brightness they have. For example, the image relating to this graph has no black and no white in it because there is no amount of brightness displayed at the very dark and very light areas. From this graph we could deduce that the photograph has a good range of mid tones and looks about right. Here is the graph you would see in Adobe Photoshop after selecting the Levels Tool. As you can see it is identical.

The Histogram Things now are starting to become clearer. The Histogram shows us a lot, and just at a glance you ll be able to tell the quality of the exposure that the camera is making.

4 The Histogram Things now are starting to become clearer. The Histogram shows us a lot, and just at a glance you ll be able to tell the quality of the exposure that the camera is making. Lets look at the photograph that the previous graphs were taken from. A cloudy day with no brilliant whites and no dark areas. This photo is about right for the conditions and from reading the graph a good exposure was achieved.

5 Testing The Histogram Now let s look at the same photo, but it s been over exposed. We should see more values of very light being recorded in the Histogram. As you can see the values recorded are towards the very light end of the scale and are very high. This shows the image is overexposed.

Testing The Histogram Let s look at the same photo, but this time it s been under exposed. We should see more values of very dark being recorded in the Histogram. The results here are interesting.

6 Testing The Histogram Let s look at the same photo, but this time it s been under exposed. We should see more values of very dark being recorded in the Histogram. The results here are interesting. We do have more values of very dark and less very light areas recorded as expected. But there is no black here at all. This is because the sky had a lot of light in it so even an underexposed photograph will not record black.

Testing The Histogram Here s another underexposed photograph. This is a better example. These results demonstrate the underexposure a lot better.

7 Testing The Histogram Here s another underexposed photograph. This is a better example. These results demonstrate the underexposure a lot better. Here we have a lot of black recorded and the levels are quite high in this area on the left of the graph. There are no whites recorded. Note the high levels of black on the left of the graph.

8 Testing The Histogram Here s another over exposed photograph. These results clearly demonstrate the overexposure. Here we have a lot of very light recorded and there are no blacks recorded. Note the high areas of white to the right of the graph.

Here is a nicely exposed photograph. From the Histogram we see that the higher values of brightness are in the middle. This shows that there is no over or under exposure.

9 Here is a nicely exposed photograph. From the Histogram we see that the higher values of brightness are in the middle. This shows that there is no over or under exposure. Testing The Histogram Note that both the very dark and very light areas of the graph are low. This is what we are aiming for. The basic idea is to keep the graph from Falling off of either edge, especially if it s a large Hump of pixels. They can be near an edge, just not dangling around the outside of it.

10 Conclusion Let s put this to a basic rule. From the photographs we ve looked at we can tell what was over exposed, what was under exposed and what was about right. Under Exposure High values of black are clearly going over the scale to the left and no white values recorded. Over Exposure High values of white are clearly going over the scale to the right and no black values recorded. Good Exposure High values are recorded in the mid area and nothing is falling off the graph scale to the right or left. 10

Advanced Reading As you practise reading Histograms you ll understand a whole lot more about how the values of black and white appear in your photographs.

Firstly, the values in the very dark and very light areas are not massively high and there is still a good range of brightness in the middle. They do fall over the graph though.

11 Advanced Reading As you practise reading Histograms you ll understand a whole lot more about how the values of black and white appear in your photographs. This picture was taken with a good exposure, but the graph still shows recorded values in the black and white area. Firstly, the values in the very dark and very light areas are not massively high and there is still a good range of brightness in the middle. They do fall over the graph though. This is because there is brilliant white in some parts of the water and brilliant black in some parts of the girls hair. But there is not much of this, so the image is fine. Note, the parts in this image where there is black and white are totally washed out pixels and cannot be changed by Post Production. 11

How to correct a contrast rejection. how to understand a histogram. Ver. 1.0 jetphoto.net

How to correct a contrast rejection or how to understand a histogram Ver. 1.0 jetphoto.net Contrast Rejection or how to understand the histogram 1. What is a histogram? A histogram is a graphical representation