'Push-Processing' to Higher ISOs

Started Feb 11, 2004 | Discussions thread
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Gordon W
Gordon W Veteran Member • Posts: 4,037
'Push-Processing' to Higher ISOs

I don't see that this has been covered lately (forgive me if it has) but in the 'old' days of photography, you could increase the effective ASA of film by simply extending the time it stayed in the developer during processing. This was called Push-Processing and the price you paid to do this was increased film grain.

A similar thing can be done with digital imagery and with the same penalty except grain is called image noise.

On a recent photo outing with some fellow STFers, I took the opportunity to try an experiment in digital push-processing when I encountered dim lighting conditions inside the Canadian Parliament Building and didn't feel like setting up the tripod yet again to do a proper time exposure.

Here is a before & after example...

Pretty amazing difference, isn't it? The top image (nearly black) is the brightest shot from a bracket of 3 taken with a Sony F707 and VCL-MHG07 wide angle conversion lens at f2.0, 1/30s, ISO 100 and shooting waistlevel with camera stabilized by pulling against the neckstrap (the Andy Williams method?).

The bottom image is the final result after post-processing in Photoshop (but could be done in any of the better image editors). All it took was placing (stacking) the 3 images from the bracket into layers in one file and setting the top 2 layers to 'Screen' blending mode, followed by some very ordinary adjustments to Levels, Curves, Saturation, and then a final touch of Neat Image.

For anyone interested, 100% crops can be seen here...

http://www.pbase.com/image/25958700/original

I don't know what the effective ISO rating would be of this procedure, but I'd estimate in this case it has to be equivalent to 1600 or higher. Not bad for a camera with a max ISO of 400 and I could have made it even brighter if I had chosen to.

This could also have been done to a single image, as would be the case if the subject is moving, but a higher ISO would have had to be used and there would be more noise to deal with since stacking cancels out a lot of noise.

However, as it turned out with this stationary subject, I could easily print it out at 11 x 14 with excellent image quality.

FWIW

http://www.pbase.com/merriwolf/

 Gordon W's gear list:Gordon W's gear list
Canon PowerShot S100 Panasonic FZ1000 Nikon Coolpix B700 Panasonic FZ80/FZ82 Nikon Coolpix P1000 +5 more
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