In this exercise we are asked to take a control picture using an average exposure and the take a series of photos starting with 1 stop over-exposed down to 1 stop under-exposed in 1/2 stop steps. To increase the arneg I chose to start at 2 stops under-exposed through to 2 stops over-exposed.
Fig 1. is a control shot at the settings calculated by the camera. Most of the time I use aperture priority and left it on that setting for this exercise. I chose f/13 to ensure that everything was in focus and the answer would not be confused by any blur.
I took a screen shot of the histogram in Photoshop for each image to allow me to see how that changes. In the control shot the histogram is weighted towards the left which is not surprise as the picture is mostly fairly dark tones.
Fig. 3 shows the series of over-exposed shots ranging from plus 1/2 a stop on the right to plus 2 stops on the left. It is very clear that the colour saturation decreases with each 1/2 stop of over-exposure. Somewhere between plus 1/2 and plus 1 stop would give the most balanced histogram.
Fig. 4 continues the sequence from less 1/2 stop on the left to less 2 stops on the right. The conclusion is clearly that colour becomes less saturated the more an image is exposed and visa versa.
It is important to be able to predict and, to some degree, control colour saturation for a number of reasons. It is part of the decision process when taking and often when post processing a picture. For landscapes I would generally lean towards under-exposure to ensure that I have captured all the detail in the highlights but also because I often want saturated colours. For example, in the bright conditions of Turks and Caicos I under-exposed by 1/3 of a stop during the brightest parts of the day. For food photography I am trying to present food in as natural a manner as possible so I will adjust my exposure and lighting to to give me a neutral result i.e. neither de-saturated or over-saturated. For portraits I am now often consciously over-exposing as I find many younger people like a slightly de-saturated look. I notice that many modern wedding photographers over-expose all their shots so I presume that this is what their clients require.