Exercise: Control the Strength of a Colour

The introduction to Part Three talks about Hue, Saturation & Brightness. Hue is commonly referred to as a colour - we name a colour (i.e. red, green etc) because of its hue. Saturation is the intensity of the colour and brightness is, well, it's brightness (bright, dark etc).

The text suggests that the theory of the alteration of colours is more important to understand for the painter, as they create their colours, whereas photographers record what is already there. Although, with some photographic knowledge, and an understanding of how a camera works, manipulation of the colours presented in a scene can be achieved at the point of capture.

The use of 'traditional' photographic filters, such as polarising filters and coloured filters (both on the lens and flashgun), as well as white balance, can also alter the colour characteristics of the image recorded. Post-capture the process of altering the colours is also now available to anyone who uses digital imagery and basic photo imaging software.

The Nikon DSLR cameras I use have 'Optimize Image' (D200) and 'Picture Control' (D300s) settings that allow the captured image to be manipulated in-camera; both cameras have 'normal' or 'standard' settings, the D300s has 'Neutral' and both have 'Vivid' - all of which alter the processing of jpeg images to suite the scene, or artistic intent. 

The first exercise is one in controlling the strength of a colour, using the controls of the camera. The aim of the exercise is to photograph a strong, definite colour, using a viewpoint that fills the frame.

The average camera reading is to be established, before a series of images are taken - one at the 'correct' exposure, then two overexposed at a 1/2 and 1 stop, followed by two more underexposed, again by 1/2 and 1 stop. The images are then to be compared and a conclusion arrived at as to the strength of the colour achieved across the group of images.

For the exercise I immediately thought of red as the colour I would use - it is a strong definite colour, and one that I thought would be easy to find at the roughly the correct hue. I then went hunting for post boxes - most of the ones I found were faded, and not sufficiently strong in colour, or in shaded / cluttered areas. So I decided to arrange a still life shot of some flowers, these were easier to arrange and I could spend as long as needed to ensure the lighting was constant before taking the shots. 

My wife was quick to point out that the only time I buy flowers is to photograph them. She may have a point...

I used a Nikon D300s mounted on a tripod, with a 105mm Macro lens to allow the petals to fill the
frame. The camera was operated by a remote shutter release. The whole set-up was arranged indoors, to prevent the flowers being moved by wind, and in front of a large window to provide even lighting.

I set the camera to ISO 200 and automatic White Balance, Standard Picture Control (Image Optimization) and Spot Metering. 

I first set the camera to Aperture Priority and selected an aperture of f11, the camera metered and set the corresponding shutter speed to 1/250th. I then switched to Manual Exposure mode, keeping the same settings and took the first image.

My camera is set to record in 1/3rd stop intervals, so I actually took 3 images either side of the 'correct' exposure to achieve the intermediate and full stop differences by altering just the aperture, the shutter speed remained the same. The resulting images are to the right.

Ok, so from the results it's easy to see the range of exposure changes, as would be expected. Depth of field will also be effected: as the aperture increases, so the depth of field will become narrower. These are by-products of the settings, but not relevant to this exercise.

Of more importance is the fact that the overexposed images look less vibrant, and the underexposed much deeper and richer in tone.

Red is a particularly rich colour, this is more evident in the underexposed images, where its 'denseness' makes for a more powerful image. Freeman (p115) talks of reds 'advancing' and 'enhancing the sense of depth' of an image - this is most evident in the -1 stop image.

My conclusion for this exercise is that slight under exposure, which is altering the brightness of the colour photographed, has the effect of creating deeper, richer colours.

Although this example deals with a single colour filling the frame - a more complex image of different colours, tones and areas of light and shade may not be able to be enhanced quite so easily.

Underexposed by 1 stop, but most vibrant