My apologies for adding confusion about negative color. I had managed
to confuse myself but, after a bit of reflection I agree with Ken and
others, those glass filters are all about scene/subject. Whether the
recipient media is negative or positive film or a positive digital
sensor the filter works the same way... it passes exactly the same
light. If the filter is red it's darkening blue and green. If the film
is negative it will respond differently than positive film but will look
the same after negative to positive conversion.
But note that that is only about using glass filters which operate by
subtracting the light not matching the color of the filter. A red
filter is reducing the luminance of everything that is not red. When we
use a red filter to darken blue skies it does so by reducing the
luminance of blue. (and the luminance of other non-red colors which may
or may not be desired).
But, when we work with positive digital images, to darken blue skies we
have to use the blue luminance slider to reduce the luminance of the
blue channel. This is the WYSIWYG feature I mentioned when doing B&W
conversion digitally.
Chuck Norcutt
On 6/16/2014 10:45 AM, Ken Norton wrote:
Duh! I had completely overlooked that! And I should know better.
So, instead of filtering with the complementary colour as we are
used to we now instead filter with the primary colour.
Uh, no. Same effect. Negative-Positive has nothing to do with it.
The filters are all about the scene/subject, not the "film". A red
filter effectively darkens greens regardless of the recording
technology.
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