Big Ben's Panorama Tutorials

Dynamic Range

Contrast

Let's return for a moment to the graphs of the data I collected.

The first graph shows the typical "S-shaped" curve that photographers expect for the characteristic curve of film.  The bottom graph shows that the contrast for this film is at no time linear.

Contrast Adjustment

Many photographers will tell you that films like Kodak Techpan have a high contrast.  I prefer to think of them as having a high dynamic range film.  Printed on the appropriate contrast paper the contrast appears "normal" AND they display an incredibly wide subject luminance range. The trick is to recognise which of these two qualities is more prevalent in your image... contrast or dynamic range. 

Having demonstrated that the images I get with Fuji Reala have a high dynamic range, it is then a case of applying the appropriate adjustments using curves to expand compressed of tones in the highlights and shadows.  This also has the appearance of reducing the contrast AND expanding the apparent dynamic range of the image.

Not surprisingly, such an adjustment looks like a charactersitic curve mirrored along the line joining the maximum and minimum values. Here is a sample curve and the effect it has on an image.

	In	Out
	0 30 60 128 180 225 255	0 60 90 128 150 205 255

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The exact values given here are for demonstration only. The degree of adjustment required depends on the dynamic range of your image. Once you have the contrast under control you can work on the colour to finish up with something like this.