Monday, 19 September 2011

Exercise: Highlight Clipping

In this exercise we are to explore the digital artefact of Highlight Clipping. This is where the brightest parts of the image exceed the cameras ability to record values (>255 where 255 is pure white or RGB 255,255,255). This causes a non graduated block of pure white which will look unattractive to the human eye.

For this exercise we are to use the highlight clipping warning on the camera and take an image where the clipping just starts. Then take another image at +1 f-stop and then another 3 degreasing by 1 stop each time. We are to note the effects of highlight clipping in the image and any effects on colour casts or saturation. Finally if taking images in RAW we are to experiment with the 'Recovery' slider in the RAW conversion process to see its effects.

The first image below was taken where the clipping was just starting in the sky and the red flowers.

The following two images are taken +1 stop at f4, the second is a screen shot of the RAW conversion showing the extensive clipping in red.

The flowers look redder but this is where clipping has occurred. It can been seen clearly that the images are washed out or faded and that the sky is completely burnt out leaving a border-less wash of white. Experimenting with the recovering slide even at 100% did not recover the sky. Whereas using this tool for the standard and -1 stop image showed great results.

The following images were taken at higher f-stops (less light through the aperture) and have not shown any significant clipping at all. It can also been seen that the skies blue saturation is visible and the red flowers more intense due to higher saturation.

Zooming into the red flowers on the left it can be seen that the red flowers are washed out and the pink flowers clipped with no distinction or border within the petals or background. The image at -1 stop has this area of the image perfectly exposed with ideal saturation and distinction.

This part of the course is leading us into the area of dynamic range and the capability for a camera to accurately record images with high contrast such as the one in this example. On many occasions it may not be possible to do this but with the use of the RAW conversion process, checking the highlight warning at the time of the exposure and perhaps using graduated filters this can be overcome to some extent.

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