[Tig] instinctive contrast

[Richard Kirk]

Hi.

Tom has explained in some detail why black and white film should have a
different appearance to colour film. There is also the Callier effect: the
silver grains diffract light where soft-edged dye clouds - which will give
you a steeper tone curve than your densitometer may suggest, because the
scattered light may be lost in a projector but not in a densitometer.

However, if I read Rob's post correctly, I think he is asking a slightly
different question: when we take out the colour from a picture, why do we
want to change the tone curve to be more like black and white film? Are we
hard-writed to prefer more contrast, and this has shaped the development
of black and white film, or has black and white film modified the way we
see things?

When I was young, and watched black-and-white 405-line TV, I used to be
aware that there were two sorts of signal - two different tone curves,
though I doubt I would have called it that at the time. You noticed the
switch between the two most when the adverts came on. The better of the
two was what you got when they showed black and white films, and the more
expensive adverts. it felt more like watching the TV with the lights out -
something we as children were discouraged from doing. The duller tone
curve was for live TV and the cheaper adverts. I am guessing that one was
done on film, and the other may have tapes or done live. While my
perceptions may have been shaped by black and white films, because we did
go to the cinema on Saturdays and only the main feature and the Pearl &
Dean adverts, and the cartoon if you got a good one were in colour - the
Pathe News, the Look at Life and the short feature would be in black an
white. If I was being conditioned, I guess it was to think of black and
white as the 'cheap' option. Nevertheless, I did seem to want to have the
black and white tone depth.

How do we see black and white images? We could imagine we are looking at a
planet lit with uniform white light, and filled with colourless objects
and people. In fact, we forget about the black and whiteness and just
accept the  strange stimulus as ordinary vision because the motion, the
edge features, the light and shadows are all familiar. The brain is good
at re-mapping stimuli and responses in this way. You stare at the field of
dots and suddenly you can see the dalmation in the leaves. There was a
documentary on the early days of the BBC, where they described a very
early outdoor broadcast system experiment. The people in the van were
testing the camera under low light conditions, when a policeman came over
and asked what they were up to. They re-wound the tape and showed him the
moving image - "here is the street lamp, here's that tree, and here you
are coming out from behind it...". The policeman looking at luminous blobs
on a flat screen could not relate it to the scene outside at all, and then
all of a sudden his brain did something and he could.

With analogue black and white TV, it is difficult to change the gamma
without lousing up the colour contrast. However, when digital techniques
became available, people like me tried increasing the luminance gamma of
still images while preserving the chroma. The result is strange, and
somehow unsatisfactory. Why? I guess a lot of this may be because we are
mentally 'wired' for colour constancy. We tend to think of 'color' as a
property of the object, and remove the effects of the illumination.
Perhaps, with a black and white image (or even with a duotone) we can shut
off our color constancy processing, which leaves us freer to muck around
with the contrast. And if you give someone a contrast control or a
sharpness control, they will tend to turn it up until they are really
damaging the image, because more signal always feels 'better'.

I think we may be taught how to see by our media. We know our sense of a
'pleasing white' varies from daylight at daylight illuminations, to yellow
incandescent at low levels - and literature has many examples of people
preferring candle-light to incandescents, though I miss my blues too much.
Nevertheless, I suggest that our preference for high-contrast images might
predate black and white photography. Evidence for this might be found by
analysing the effective tone curves of etchings and line drawings in the
history of art. I think Charles Poynton may be going to do just that, so
maybe sometime soon we shall have a proper answer, instead of just me,
guessing.

Cheers.
Richard Kirk
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