Arnoud Quanjer Wildlife Photography

Please only read this article if you use RAW mode on your camera. If you shoot in JPEG mode then exposing to the right doesn't make any sense at all so reading this article would be a waste of your time. If you shoot in JPEG mode then please consider changing that habit. I'll write an article about the advantages of shooting in RAW mode in the near future.

A digital SLR has a dynamic range of around 5 stops. When working in RAW mode most cameras record a 12 bit image. A 12 bit image can record 4,096 (2^12) tonal values. One would assume that the recording of tonal values would be evenly distributed between the 5 available stops. If this was the case then each stops range would be able to record 820 (4096 / 5) of tonal values. Unfortunately this is not the case. The recording of tonal values is not evenly distributed among the stops. Most of the tonal values are recorded in the first (and thus brightest) stop. This stop can record 2048 and thus half of the available tonal values. The reason for this behaviour is caused by the design of the CCD and CMOS sensors. These sensors are linear devices and as each stop records half of the light of the previous one it follows that about half the tonal values will be recorded in the first stop. 

If you look at this table then you'll realise that if you don't use the 1st stop that you'll lose the recording capability for half of the tonal range. Most of the books and websites will tell you that if the colour histogram of a picture is centred in the middle that the exposure will be correct then. Although that might be true in most cases it also means that you lose a significant portion of the available tonal range which your sensor is able to record. To make sure that you record the maximum number of tonal values you should make sure that you 'expose to the right'. This means that the brightest part of the colour histogram (the right) should be aligned to the right of the tonal range. The risk in exposing to the right is blowing the highlights by overexposing too much. Overexposure will be shown on most camera's by white blinking alerts on your LCD.

If you look at the pictures that you've 'exposed to the right' in your RAW conversion software then you'll notice that the image is too light. Just adjust the exposure by using the brightness and contrast sliders so that the tonal range will be spread out evenly. What this accomplishes is that it will minimise signal to noise ratio and it will posterization and noise that potentially occurs in the darker regions of the image. The shadow regions of your images will now consist of more tonal values than when you would have centred the colour histogram when you took the picture.

Make sure that you're working in 16 bit (12 bit) mode while making the image corrections in a RAW converter. In RAW mode your camera is not doing any non-linear processing, all of the non-linear processing will be performed by your RAW converter. This is why you have to shoot in RAW mode if you're going to use the 'expose to the right' method. Be aware though that if you're going to 'expose to the right' you're overexposing your shots and thus you're lowering the shutter speeds. If you're not using a tripod for your shots then this might lead to camera shake at low shutter speeds. The first priority should always be a sharp picture so if 'exposing to the right' means you can't get a sharp handheld picture then use the conventional exposure method and expose for the middle.