Re: contrast

From: Mitsu Hadeishi (email suppressed)
Date: Wed Jul 12 2006 - 09:37:55 PDT

On Wednesday 12 July 2006 10:56, david tetzlaff wrote:
> The meaning of the terms 'contrast' and 'contrast range' are well
> established in the history of photography, and are inverse to one
> another. Any photography manual will tell you that high contrast is
> produced by having a low contrast range. Kodachrome looks more snappy
> than BW negative because it has more contrast, but the later has more
> ability to capture detail.

I understand what you're getting at, but while you're right in some sense,
you're not right, because you're thinking about what happens when you have a
fixed medium (whether it is photographic or video makes no difference) and
you try to increase the contrast, whereas what we're talking about is
absolute contrast as well as dynamic range of *different* media.

That is to say, for a given medium, increasing the contrast of the image will,
of course, decrease the contrast range ... there you are perfectly correct.
But if you show the same image in two projectors adjusted to maximize
contrast range, then the contrast is simply defined in mathematical terms by
(Lmax - Lmin) / (Lmax + Lmin), and what I am calling a "high contrast"
projector will exhibit a higher contrast for that image than a "low contrast"
projector. Again, if you wanted to take a single projector and adjust it so
the image appeared more contrasty, then you'd be right, the result would be a
crushing of the blacks and a flattening of the whites, but that's not what
we're talking about here.

Thus, when people speak of "high contrast" projectors they mean projectors
with a high contrast range, which will appear subjectively to show the same
image with a higher contrast. (i.e., it's quite evident if you view the same
video content on a high contrast versus low contrast projector, when adjusted
properly, the low contrast projector images have washed-out black levels and
have lower contrast in mathematical terms.)

> Neither term refers to the ability of the medium to reproduce a black
> that is actually black and a white that is actually white, that's
> something else (I forget at the moment). In effect however, contrast
> range specs for video projectors probably correlate to deeper blacks,
> but that's not what 'contrast' means. Your formulation beloew is
> grammatically equivalent to "strong stomach (cancer)."
> Perhaps, when/if photochemical imaging recedes into the past the word
> 'contrast' will undergo a full meaning-shift, (going back to the
> 'contrast' knob on TVs, which doesn't actually adjust contrast)...
> but not yet.
> >The best projectors have dark blacks AND a wide range of grey
> >levels, so I think it's more accurate to call these "high contrast
> > (range)" projectors.
> __________________________________________________________________
> For info on FrameWorks, contact Pip Chodorov at <email suppressed>.

For info on FrameWorks, contact Pip Chodorov at <email suppressed>.