If you ever attended mathematics or geometry lessons during your school days you’ll have covered line graphs and bar charts to help display how many red cars drove past together with the amount of blue and yellow cars etc., in other words the aim was to present the information clearly using a chart. Well, now that we record digital information when pressing the camera’s shutter button we need to present the data in a way that shows the various amounts of light levels; only this time it’s the amount of light, medium and dark. But why? you may ask, welcome to one of the major tools we now have in our cameras that we didn’t have when using film, the histogram.
Previously, the exposure of a photograph was shown by a needle on a light metre which moved up or down when it was pointed at the various light levels in a scene. Now, thanks to clever ‘wizardry’ in your camera, the various light levels are collected together and shown as a kind of bar chart both before and after taking a shot.....the chart is your histogram. So if there’s no needle how are the various levels of light seen? If by now you have been able to grasp the notion that your images are made up of pixels and that each pixel records an amount of light then you will be on track for recognising that it’s similar to recording the number of ‘cars’. The histogram can be accessed via your camera’s menu and it can be shown (or not shown),on the LED screen. Some cameras let you view the histogram in the electronic viewfinder.
All histograms display the various levels of light and all work on the basic of showing the amount of pixels that are dark on the left-hand side and all the pixels that are bright on the right. The mid-range levels of light or ‘tones’ as they are called, are shown in the middle; so what’s the point of all this? In a ‘nut shell’ it helps you to see if your image will be (or is) under or over exposed. If the majority of ‘peaks’ in the graph are shown on the right it tells you that your photo will be (or is) overexposed i.e. it’s going to look to bright. You are being told the reverse if the ‘peaks’ are on the left and you can expect an image to be underexposed, i.e. too dark.
You should remember however, that the histogram is a guide and that you are in charge. By changing any one of the 3 members of the ‘exposure triangle’ you will see the pixels peaks change in height and distribution along the scale. It will slow your picture taking down a little but it’s worth giving time to make adjustments. You can however, make similar changes to the histogram if your editing software shows the same details but as always, its best to try and get it right in the camera first.
Some histograms will show the images in black & white while others will include a red line, a blue line and a green line this is because all digital photos are made up of a mixture of these three colours. A more in-depth explanation will come into play when your involvement in post processing increases suffice to say you are able to dig deeper into adjusting an image by looking individually at each colour or channel as it’s called.
If at any time you see the peaks falling off the scale on the right-hand side it means you will be losing valuable data in the highlights of your photo; this is referred to as ‘clipping’ and its always best to try and avoid it as much as possible. Again the reverse applies on the left-hand side only this time you will be losing valuable data in the shadows. This subject can become more complicated but suffice to say, knowing the basics will help no end.
So where are we?
* The left-hand side of the histogram shows how much digital information has been recorded in the
shadows. The right-hand side shows how much digital information has been recorded in the
highlights; between the two ends are the mid-range tones.
* The graph / histogram shows you what your current camera settings are going to give you in your
* The more ‘peaks’ (i.e. amount of pixels) on the right of your histogram, the brighter (that’s overexposed)
the photo will look.
* The more ‘peaks’ on the left of your histogram, the darker (that’s underexposed) the photo will look.
* Many cameras give you the choice to turn the histogram on or off which is good if your screen is
smaller than you would like; check out your camera manual to see the choices available.
* Don’t get ‘hooked up’ on this, the histogram is a guide but I would advise you to slowly use it more as
time goes on.
* It’s a tool and as with all tools they work for you and they should not stop you from being creative.
* To bring the ‘peaks’ more towards the middle, you need to decide if you should alter the shutter speed
or the aperture or the ISO...here in lies your creative freedom.
Thanks for reading, I hope you found this useful.
Terence Jones ARPS
A photography enthusiast with a long and varied interest in taking pictures.
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