Contrast Masking: english - deutsch
Contrast Blending: english
Color negative film is able to capture a far higher dynamic range as digital cameras or even slide film. I made a small test to determine how much and took some photos from one of our rooms.
In the darkest part of the image (the speaker cones) I measured an exposure of 30 seconds f/8. In the brightest parts (the white sunlit wall) 1/250 f/8. This is a dynamic range of more than 12 f-stops.
The images where taken on Fuji Reala and scanned with a Nikon Coolscan IV ED (LS-40) and vuescan with automatic exposure but without color balance and histogram clipping.
In photoshop the histogram was clipped to the very brightest and very darkest pixel. The corrected versions where treated with my contrast masking actions using not the curve adjusted mask but the saved original mask for the highlights channel. This mask was adjusted with levels control to reveal the outside scene and to hide everything inside.
The goal of the corrected versions was to show how much information is still in the scan, not to optimize for image quality.
(please click on the thumbs for a bigger version)
The dark corner needs 8 seconds exposure time for a good result. The black speaker cones are clearly visible. The outside scene looks pretty overexposed, but there are no regions clipped to bright white.
The contrast masked versions shows relatively saturated colors and good contrast for the outside scene, although there is a slight color shift. Only the highlights mask was used, no need for the shadows mask.
With 1 second exposure the speaker cones look almost entirely black whereas the outside scene is still overexposed.
This image was far easier to correct: The highlight mask gives reasonably good contrast and saturation. The shadows mask reveals some detail even in the black speaker cones.
1/8 second exposure is far too low for the inside scene whereas the sunlit walls look pretty good.
The shadows mask can help a bit here, but the result is very grainy. The darkest corners are beyond repair.
1/60 second would be the correct exposure for the sunlit part (at least if taking slides ;-). Inside there seems to be pure black.
Even here the shadows mask reveals some details but most of the area is grainy and without any structure.
© Erik Krause 2003