“Take three or four exposures of the same scene. Don’t change anything on the camera and keep the framing the same. Preview the shots on the LCD screen. At first glance they look the same, but are they? Perhaps a leaf moved with the wind, the light changed subtly, or the framing changed almost imperceptibly to include one seemingly insignificant object and exclude another. Time flow, the moment of each frame is different, and, as the saying has it, ‘you can’t step into the same river twice’.
Now bring up the histogram on the preview screen. The histogram is a graphical representation of exposure – the camera’s sensitivity to light. As you page through the images you can see small variations in the histograms. Even though the pictures look the same, the histogram data shows that in a matter of seconds the world changes, and these subtle differences are recorded by the camera. If yourefine the test conditions – shooting on a tripod to fix the framing, moving indoors and closing the curtains to exclude daylight – still the histogram changes. Probably some of the changes are withinthe camera mechanism itself; still, the camera is a sensitive enough instrument to record them.
Add the sequence to your learning log with the time info from your camera’s shooting data as your first images for Part 1”
My Learning Log for this exercise
These four photos were taken with my Canon 6D, Lens 24-105, mounted on a tripod. As instructed the camera was set to auto. They are of the Swing Bridge in Ramsey.
IMG 0783 29/09/2016 15:45
IMG 0784 29/09/2016 15:45
IMG 785 29/09/2016 15:45
IMG 786 29/09/2016 15:46
In looking at the histogram it is very difficult to see any changes initially between the first and last photos. I looked at the article online by Steve Patterson, How to Read and Understand Image Histograms in Photoshop (accessed on 3/10/2016). He describes a histogram as showing the ‘current tonal range of an image so we can evaluate it and, if necessary, correct it.’ He goes on to describe tonal range as being the brightness of the image and that it shows the amount of pure black, pure white and the range in between. Colour also can have a huge impact on the image. So relooking at these photos I can instantly see that they have been clipped at the white end of the histogram which means there is likely to be blown out highlights which have lost the detail. I can also see at the peak of the small bump in the histogram subtle changes in the yellow and red channels.
The height of the bumps in the histogram show the level of brightness in comparison to other levels of brightness. So the taller the ‘mountain’ the more pixels there are at that brightness level or where there are none there are no pixels at that brightness levels as at the very left on my photos. A ‘good’ histogram would have an even spread across the range of the histogram – thus my camera set on auto has not taken a good tonal range as it is clipped at the right end of the histogram and has an empty space at the left. This means the auto setting has over exposed the picture. This can be seen in looking at the photo – there are burnt out areas both in the water and the sky and both lack detail.
Patterson, S. (date unknown) How to Read and Understand Image Histograms in Photoshop. Accessed on 3/10/2016.