Learning Technology: Photography for Elearning Developers

Photography for Elearning Developers - Working with a Histogram:

If you've owned a prosumer camera or a DSLR/ SLT, you may have seen the histogram display on your camera. It may have even left you confused. One of the more ignored tools in your arsenal, the histogram is a great diagnostic for your image. Taken step further, it's also a pretty awesome guide to post process your image.

In today's post I'll explain this really useful graph to you. Don't worry - you don't need to be a scientist to understand this. It's quite simple.

So what's a histogram really?

In simple terms the histogram displays the distribution of blacks, whites and middle greys in your picture. The key mnemonic to read a histogram is this 'dark to light, from left to right'. The left half of the histogram shows the distribution of shadows and the right half displays the distribution of highlights. The x axis of this graph starts from a pure black and goes on until a pure white. Everything in between is a shade of grey.

Not all histograms look like a bell curve as you see in the above picture, but what you should try and ensure is that you don't have too much of pure whites or pure blacks in your image. Why is that? That's because the textures and play of light in real life ensures that situations in which you see a pure black or pure white are unusual. The situation when you have a lot of whites (also called 'highlights clipping') indicates that you may have over exposed your image. As a corollary, if you have too many blacks (shadow clipping) that may mean you've underexposed your image. Makes sense?

There are situations when you'll have both shadow and highlight clipping. These are very tricky. Usually this happens in awful lighting situations where you perhaps need to underexpose to overcome the highlight clipping and use artificial lighting to bring out the detail in shadows. Unfortunately these situations are difficult to post process as well. This is one of the reasons it is a good idea to get the right exposure out of camera. Here's a video explaining the concept visually.

Post processing - Creating a high key or low key photo

One of the great things about a histogram is that it tells you exactly what you need to do to give your image a professional pop. The easiest thing you can do is move the middle grey slide in Photoshop (any other tool will give you a similar interface) to either darken the shadows or lighten the highlights further. If you move your slider too far to the right, you'll get a low key image (eg: here) and of you move it far left, you get a high key image (eg: here).

Post processing - Improving tonal range using Levels

One of the most useful images you'll see on Photoshop is the Levels tool. Before you understand how to use it you need to understand histograms - which you already do to a great extent. The key to a good image is that it should ideally have a range of greys in the shadows and highlights with no pure whites or blacks but almost every other shade. So, the wider your histogram, the more contrast in your picture. Now you will also have a lot of contrast if you had a lot of highlights and shadow clipping, but this will mean that you'll get a very black and white image! So you need to avoid that one.

In a lot of photographs you may be able to go with some amount of shadow clipping because extremely dark places usually will show up as pure blacks. In rare circumstances - and remember they are rare - you might be able to live with some highlights clipping too. But for the most part, the levels tool should be able to help you modify your histogram and shift the white point and black point inwards. By doing this, you're effectively spreading your original histogram over the entire tonal range from white to black, thereby increasing the contrast. Take a look at this video to see how you can create a nice, pleasing, contrasty image with the levels tool. It really helps add a professional pop to your image. And by the way, you should be able to use similar tools on any other post processing package.

So, try this tool as the basic post processing on your images and also as an in camera diagnostic for your exposure. You'll notice that being able to read the histogram is a really useful skill. Hope you enjoyed today's blogpost. More to come in the next one.