Explain Bleach Bypass to me...

Chris Keth · November 13, 2004

I keep seeing this mentioned. What is the process and what's it do to the image?

David Mullen ASC · November 13, 2004

Have you checked through the archives to see if we've answered this question before? It seems it comes up every two months or so.

If you can't find the old answers, THEN I'll answer it, I promise... IF you tell us your real name.

Chris Keth · November 13, 2004

I didn't find one post that explains it well so let's see if I got it all right. To satisfy your demands (:)) my name is Christopher Keth. I'm a film production student at the Rochester Institute of Technology sppecializing in cinematography.

So I get that it's skipping the bleach bath entirely (hance the name) of color processing, right? It will have the effect of desaturating colors and increasing contrast in the image, right?

Now, is it done on the negs or print?...or can it be done anytime in the process to different effect?

David Mullen ASC · November 14, 2004

Silver halides respond to light and become developable (carry a latent image) in both b&w and color film. In color film, when processing the silver halide, exposed grains develop into metallic silver but color couplers in color film form dye clouds in the same area and to the same degree, in each color layer.

Then color film normally has a bleach step to convert developed silver back into silver halide so it can be removed by the fixer and wash steps along with the unexposed silver halides that never developed into metallic silver. Skipping the bleach step leaves developed silver in, "polluting" the colors with black silver. Contrast is increased and color saturation is decreased.

When done to a print, skip-bleach causes the blacks to be denser than normal so most of the loss of detail is in the shadows.

When done to the negative, there is an increase in density in the bright highlights (where there is already the most density on a negative), causing them to burn out faster. There is also more graininess than when done to the print because camera negative stocks have much larger silver grains than print stock (print stock being an incredibly low ASA.) Most people doing a skip-bleach process to the negative will underexpose to compensate for the increase in density, or else the image may be printing in the 50's.

steveb40 · November 15, 2004

Silver halides respond to light and become developable (carry a latent image) in both b&w and color film. In color film, when processing the silver halide, exposed grains develop into metallic silver but color couplers in color film form dye clouds in the same area and to the same degree, in each color layer.

Then color film normally has a bleach step to convert developed silver back into silver halide so it can be removed by the fixer and wash steps along with the unexposed silver halides that never developed into metallic silver. Skipping the bleach step leaves developed silver in, "polluting" the colors with black silver. Contrast is increased and color saturation is decreased.

When done to a print, skip-bleach causes the blacks to be denser than normal so most of the loss of detail is in the shadows.

When done to the negative, there is an increase in density in the bright highlights (where there is already the most density on a negative), causing them to burn out faster. There is also more graininess than when done to the print because camera negative stocks have much larger silver grains than print stock (print stock being an incredibly low ASA.) Most people doing a skip-bleach process to the negative will underexpose to compensate for the increase in density, or else the image may be printing in the 50's.

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Wow. That's an excellent explanation to a complex process. So did Kaminsky light every scene (Minority Report) especially for this process (more or less fill) and underexpose?

David Mullen ASC · November 15, 2004

Well, to some degree, Kaminski didn't try to counteract the contrast build-up nor the blown-out highlights. Articles on the film don't mention how he rated the stocks. I'm sure he shot tests though to know when to watch out for a highlight that was too hot or a shadow that was too dark, although I'm not sure if Kaminski has ever met a highlight that he thought was too bright.

Smoke on the sets helped though to lower the contrast. Plus the whole movie was shot with diffusion (Dior nets on the lenses.)