Note to Self: Use the histogram!

The S95 has made me really aware of the histogram. The live histogram shows only luminance but is very helpful in adjusting exposure compensation. This little camera’s sensor really needs careful thought for better images. As much light as is possible whenever possible is the mantra. Shifting the histogram to the right until just before clipping really helps. The exposure control is used in almost every picture I take.

But there is more: The histogram only shows the luminance not each red/green/blue-channel. On the average the individual channels match the luminance, and the luminance histogram is sufficient: No clipping in the luminance and the individual colours won’t clip either. Depending on the subject and lighting the threee colour channels may show a slightly different reality.

The picture below is underexposed according to the luminance histogram in the lower part of the screen shot below. But still the colour histograms to the right indicate clipping in the red channel. The result is that colours, specially red-ish ones of course, will be off and not true. In this shot I know the frisbee’s colour to be just about right, even though it probably isn’t – the histograms don’t lie!

The luminance histogram shows a sufficently large guard zone until clipping but still the red channel clips!

With no manual underexposure the red channel is severly overexposed and the pink frisbee turns out entirely different in colour, as below:

Here the luminance histogram is clipping and every colour channel also. The result is that every bright colour is completely destroyed and more or less white. 

Any channel that is clipping shows the same intensity for all clipped areas. Mixing Red, Green and Blue in equal proportions give us white areas.

Conclusion: Use the RGB-histogram! On the S95 it is only available after the picture is taken. Better late than sorry I imagine. The overexposed, clipped picture above was taken with +2/3 stop manual exposure compensation. The better, underexposed was taken with -1 stop manual exposure compensation. Both at f/2.

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