[opendtv] Re: RGB mania
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 16 Jan 2005 21:01:43 -0000
Doug, I'm with you 100% here. Just take a look at any of the published data
curves for film stocks, like 5279 or 5277 and you'll see a clear linear
slope in the D/LogE curve, which means a power law. And we happen to call
that "gamma".
----- Original Message -----
From: "Doug McDonald" <mcdonald@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Sunday, January 16, 2005 6:33 PM
Subject: [opendtv] Re: RGB mania
> Craig Birkmaier wrote:
>
>
> >
> >>You set the blackest black well up on the toe if
> >>you want details in the blacks. If you don't, by definition
> >>you lose detail in the blacks! I'm not saying you have to set
> >>it up above the toe into the linear gamma region, of course.
> >>But if you want detail in the blacks (Zone 1) you MUST get them
> >>well up onto the toe. As I said, I have never seen a movie with
> >>detail in Zone 1. Stills, in photo art galleries, yes, they are
> >>a "dime a dozen". Movies, no.
> >>
> >
> >
> > I think you are out of your league here Doug.
> >
> > What gamma are you talking about? There is no gamma in film negative,
>
> There most certainly is. Most certainly, most emphatically,
> most traditionally for "time immemorial".
>
>
> > although there are both linear and non-linear ranges for negative
> > density in the normal response curve. If you set the blackest black
> > at the point where the density response turns linear, you have thrown
> > away all of the potential for detail in the blacks.
>
>
>
> A negative film curve, density versus log exposure,
> starts as a horizontal line at the bottom left (below the toe),
> then rises up with upwards curvature (toe) into a linear
> region (the slope of which is gamma) and then at high
> exposures it has a downward curvature region (shoulder)
> then a flat region and, perhaps, goes down again (solarization.)
>
> You say "If you set the blackest black
> > at the point where the density response turns linear, you have thrown
> > away all of the potential for detail in the blacks" . This
> is implying the part that is "below the toe". You actually mean
> where it is flat, not linear. Linear is above the toe, into
> the region where gamma is pretty much constant in most film.
> When I say "If you set the blackest black
> > at the point where the density response turns linear" I mean
> into the linear region, at an exposure just above the toe.
>
> >
> > Gamma is a uniquely video/display concept.
>
>
>
> Uh, no. Gamma is just the third letter of the Greek alphabet.
>
> It is a symbol for many things. And one of those is film gamma.
> Typical pictorial camera negative film gamma is 1/2, though you can vary
> it from 1/6 to over one with different development, and some film types
> have gamma as high as 5 or occasionally more. B&W print paper comes in
> different grades, from gamma about 1 to about five. The "curves"
> feature of Photoshop is a convenient way to simulate the effects
> of changing print gamma.
>
>
> Doug McDonald
>
>
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