Exposure and White balance – why they are not the same thing

Meet Brian Child

Image of Brian Child relaxed at work

Brian Child relaxed at work

We work together. Most of the time this is how Brian looks….

Brian Child on the phone

Before 9:30am and pre black eye

But by 9:30am he usually looks like this….

Image Brian Child dealing with it

Business as usual

One day he bought his Nikon Camera into work. In discussing the camera he said what he wanted to know was how to take a picture of someone against a bright background without loosing them as a silhouette.

We soon got discussing about Center weighted average meeting which got confused into White Balance.

At the time I could not adequately explain that ‘exposure’ and ‘white balance’ were completely separate things until of course arriving home. As I looked at these pictures I realised these showed exactly what I had tried to say but had not got across. So without further ado lets meet Brian Child again.

Image Highlighting the important parts of picture of Brian Child

Points within the picture that tell a story

Was it too obvious?

This is a picture of Brian Child sat in front of a window. And he’s not in silhouette.

The photo has been modified in the followings ways only:

  • A 10% sharpening using The Gimp
  • Resizing the picture for illustration here

There is no ‘catch light’ in Brian’s glass’s, so this photo was not taken using flash. It also explains why it is a little ‘soft’ as there is an element of camera shake. The digital image information shows the shutter speed was 1/25th of a second at F2.5 or an EV [Exposure Value of 2.66] I’ll probably return to Exposure Values in another article.

Further illustration is worthy on the following points:

Point A, B and C

We are sat within an office. The walls are finished in white paint. Why does point A show up as a light green colour? The answer is to do with White Balance. We can see that we have achieved white balance at point C, an open book of white pages and point B that is white painted wooden window frames. Therefore the white balance is correct.

Point A is green because it is picking up the green cast from the overhead fluorescent lighting used within the office. It is in shadow from the light streaming through the window but is picking up the reflected lights from the overhead lighting. This shows that White Balance is a function of the lighting being used to illuminate the scene.

Therefore you need a different white balance setting for daylight from Fluorescent lighting to tungsten lighting. Your exposure is your exposure and is nothing to do with White Balance.

Point C, the book, is reflecting the light streaming in through the window.

Point D

This area is in complete shadow and has lost all detail. Its a compromise of not having used a flash. Had I used a flash this area would have had some light pumped into it revealing its detail.

General discussion

The contrast range of this picture has exceeded the ability of our digital camera to resolve. In other words the highlights are washed out showing little detail while the shadows, point D, are devoid of detail too. However this does not distract from the fact that this is a candid picture of Brian at work, Brian had only just noticed I was taking pictures of him. What gave this away was the beeping from the Digital Camera as Digital Camera’s have a habit of doing unless you turn it all off. Noise and intrusive nature are at odds with candid photography.

How was the exposure determined?

Centered Weighted Average Exposure?

This term is from the days of film camera’s, but I suspect its still similar in today’s Digital Cameras. The manufacturer has assumed that most of the time you will position what is most important to you in the middle of the frame. If you compose your pictures before taking them as likely what most interests you won’t be in the middle of the picture. In other words this feature is to help the masses achieve a reasonable exposure.

Brian is not in the middle of the picture is he. Besides even if he was there is so much light coming through the window that this is likely to upset the camera’s metering and get the wrong result – Brian in silhouette.

What I do is to point the camera down towards the floor – this does not mean at the floor. It means to point it towards an area in the scene that is more representative of the overall lighting in the room or space where I am taking the picture.

But be aware!

Because I was using an Auto Focus digital camera without through the lens viewing.  In other words a pocket digital camera and on the whole I don’t like to look through the view finder anyhow! This means you must choose a part of the scene that is the same distance from you as the part that you want to shoot. Otherwise your exposure will now be almost correct but your focus will be out!

You are blessed

With a digital camera and the ability to take many pictures and change out a memory card when you need, not to mention you can get a good idea of what you’ve just taken on the Lcd screen, there is no excuse for not taking many more pictures and experimenting.

So try it different ways and try using your camera without looking through the view finder – but with intelligence and you’ll be surprised.

Advanced stuff

I mentioned that the scene exceeded the camera’s contrast range. To compress the range, or in other words to reduce the difference between how bright the day light is and how dark the shadow is we can reduce this by using a Flash. This puts light into the shadows and therefore brings up their exposure closer to that of the daylight. Thus the difference between the highlights and shadows are reduced.

In using a flash, light would have been pumped in to area D lightening this area up, reducing the scenes contrast ratio [amount of light in the highlights and depths of the shadows] it would have also ‘frozen’ Brian too by making the exposure much shorter and therefore sharper.

So why don’t you?

The essence is my style of picture taking.  I like ‘candid’ photography which is as unobtrusive as possible and that means no flashes going off. I hail from the days of black and white photography with hand held light meters, developing prints and films in a darkroom.


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