This bit of education is worth its weight in gold. :) Thanks Ken.
Richard
On 9/21/05, AG Schnozz <agschnozz@xxxxxxxxx> wrote:
>
> > Based on his darkroom experience, AG wrote about the behaviour
> > of the E-sensor compared with analogue imaging, and mentioned
> > the "shoulder" and ?? I forget, the "heel".
> > For the sake of one who unfortunately has no darkroom
> > experience, could you please elaborate, AG?
>
> A scene as captured by a sensor will have five distinct
> brightness levels of which I'll refer to in this response:
>
> Pure White
> Light
> Midtone (average brightness, 18% grey, etc.)
> Dark
> Pure Black
>
> Assume for a second that we expose a scene for the midtone
> exposure so that it is captured at exactly the same level on
> color print film, slide film and digital capture. When doing
> so, you will see the Light and Dark portions pretty well match,
> except for the nuances which are "signature characteristics" of
> a given film type.
>
> Where the differences come in is in the transition between Light
> and Pure White as well as Dark and Pure Black. For example:
>
> Fujichrome Velvia has a hard transition between Dark and Pure
> Black. There is no "toe" to the film, as anything below a
> certain brightness value is pushed downward to black. However,
> most print films have a gentle transition between Dark and Pure
> Black. As the real life brightness level decreases, the film
> isn't linear in the falloff and will continute to show something
> down in the deepest of shadows. In essence, a print film with a
> toe is pulling dark values up away from pure black. Digital is
> between these two film types and attempts to capture a linear
> response down to the point where sensor noise is the limiting
> factor. Better cameras, such as the E-1, will fudge a fake toe
> to give you the feeling of a gentler transition between Dark and
> Pure Black, but it does so through the stretching of the
> midtones.
>
> So, as a general rule, "Toe" is the hockey-stick curve between
> the "Straight-line Response Section" (or linear response) of the
> film/sensor and the Pure Black.
>
> The "Shoulder" is the opposite end of the spectrum. This is the
> transition between Light and Pure White. Classic thick emulsion
> B&W films would have a shoulder that went on forever. You could
> keep detail in bright clouds while having your midtones in the
> proper position. Again, digital cameras are pretty well linear
> in reponse, but will fudge a slight shoulder to match film a
> little bit.
>
>
>
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