DPP: Part 2 ? Digital Image Qualities: Exercise 6 ? Highlight clipping
April 3, 2013
This image required a scen with a wide range of brightness. I chose a canal lock scene, set against the sky as there’s a reasonable range – from shadows in the lock, to the bright ends of the lock gates. Here’s the scene:
As the exercise instructs, I set up my camera so the highlight clipping warning just appears. The settings were ISO 100, 1/30s exposure and an aperture of f/16:
I then took four additional shots – increasing the exposure by one stop each time.
The next step was to review the images on my computer – comparing the various aspects of the highlight areas:
Completely lost areas of visual information
Between the first and second images there’s a clear loss of detail in the branches of the trees, with them seeming to “blur” into the sky:
By the final image even details in dark areas have more-or-less disappeared:
A visible break in the form of an edge between nearly-white and total white
Even in the first image, this is evident, where the white ladder is set against the light-grey sheds in the background – it merges with a solid block of white, with no clear form to it:
A colour cast along a fringe bordering the clipped white highlight
A “halo” of colour is actually already evident in the image above on the left-hand-side of the ladder – most obvious where it cosses the black lock gate. However, it’s even more evident in the second image – as shown below:
In later images it disappears, as details become blown-out:
The colour saturation
The blue sky is reasonable in the first image, but by the second image it’s los saturation and is hard to distinguish from the clouds scattered across it:
Overall, the image taken without any highlight clipping, at the top of this post, has a far more pleasing tone to the sky.
The final part of this exercise is to experiment with the “Recovery” tool in my software. This makes use of data from the different colour (RGB) channels to “rebuild” clipped channels – taking advantage of the fact that the different channels don’t always clip at the same time.
I noted with very high levels of recovery white areas seemed to become grey-ish and the whole image seemed duller in tone. On the images with a lot of clipping it would bring out edges, but detail was clearly not available.
I set the Recovery to 45 on the first image, which brought out some background detail without negatively affecting the overall image too much – this was the result: