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Monday, 14 June 2010

Control the strength of a colour

This excise is about exploring the relationship with exposure and how this can affect colour. The idea being to find the average exposure of a strong definite colour then varying by half stops either side of this average, take a sequence of images then compare the differences in terms of colour.


I used natural light through patio doors for this exercise and had set the camera up on a tripod so that each exposure was of the same viewpoint and frame plus I used a manual white balance setting to further ensure the consistency. The subject is the back of my wife’s wedding dress (yes she got married in red!). I used an automatic mode on the camera to identify an average exposure this was f/5.6 at 1/15 sec (I had set the ISO at 200 and have used a fixed 50mm lens).

I Then set the camera to manual mode and started the sequence by 2 half stops of the average exposure  then took an image at each half stop decrease in the aperture size.


50mm f/4 1/15 sec ISO 200


50mm f/4.5 1/15 sec ISO 200


50mm f/5.6 1/15 sec ISO 200


50mm f/6.7 1/15 sec ISO 200


50mm f/4 1/15 sec ISO 200 

To make it easier for comparison I created a version with each individual shot beside each other in order of exposure.

The exercise showed that as the exposure changed so did the colour; but when I say colour, I actually mean the Saturation and the Brightness of the colour and not the Hue (the photographs are predominately red which doesn’t change). With the overexposed  images being more bright with a weaker saturation and the underexposed images being darker with more intense saturation.

To strengthen the point I loaded the files  into Photoshop where I changed the preferences to display colour information in the HSB(Hue Saturation Brightness) mode and then selecting the same area in each of the frames, I ran the pointer over the most overexposed image (image1) and compared the results with the most underexposed image (image5).

In the overexposed image (image1) as I ran the pointer over a small area, the Hue varied around 0-10 Degrees, the Saturation varied between 30-80% and the brightness was consistently around the 90-100%

In the underexposed image (image5) as I ran the pointer over the same small area, the hue again remained about the same displaying figures around 0-10 degrees, however the saturation was more consistently displaying much higher figures of 80-90% and the brightness was consistently a lower percentage of around 60-90%

Although I can’t exactly quantify the figures, it certainly backs up the theory and the findings from my visual assessment in that the underexposure produced the greater depth and darkness to the colour, whilst the Hue remained unchanged. 

Despite my reservations with the colour section I really enjoyed this investigation.

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