OK. This is a true duotone in the original sense.

When the subject dynamic range far exceeds
the normal ability of the reproduction medium
to reproduce/display that DR, one must divide
the subject DR into two [or more] exposures,
each of which deals with a different part of the
subject DR. Each exposure successfully records
and reproduces its own designated section of
the total subject DR. Then these exposures are
overlapped to create the final reproduction with
a greater tonal range than can be achieved via
a single exposure.

The original use of duotone involved halftone
screen reproduction of images [chromes and
prints] whose DR was beyond the reproduction
range of a single halftone exposure. These
halftone negatives are used for making plates
for offset presses [ink]. So, you shoot one
shot for the shadows and mids, and let the
highlights block out [highlights will then not
print]. The you shoot another halftone shot
for the upper mids and lightest tones, at a
very low contrast.

Both of the above shots are used to make
separate printing plates. The printed page
will carry perfectly overlapped impressions
from the two printing plates. It's similar to
how to make a 4-color [CMYK] print run,
but instead of 4 colors, there are only two,
and both of them are black ! OK, they can
be warm black and cool black if desired to
print cool shadows and warm upper tones.

That is WHY duotone is called DUOtone :-)

If the above sounds very similar to HDR in
digital photography, then you understood
the explanation very well !

Soooooo .... the image below, which is in
MONOchrome is actually a true duotone ...
cuz it's an HDR image, as needed for the
crazy DR of such subject scenes. The HDR
process is just the digital child of duotone
offset printing :-)

.

OK. This is a true duotone in the original sense.

When the subject dynamic range far exceeds
the normal ability of the reproduction medium
to reproduce/display that DR, one must divide
the subject DR into two [or more] exposures,
each of which deals with a different part of the
subject DR. Each exposure successfully records
and reproduces its own designated section of
the total subject DR. Then these exposures are
overlapped to create the final reproduction with
a greater tonal range than can be achieved via
a single exposure.

The original use of duotone involved halftone
screen reproduction of images [chromes and
prints] whose DR was beyond the reproduction
range of a single halftone exposure. These
halftone negatives are used for making plates
for offset presses [ink]. So, you shoot one
shot for the shadows and mids, and let the
highlights block out [highlights will then not
print]. The you shoot another halftone shot
for the upper mids and lightest tones, at a
very low contrast.

Both of the above shots are used to make
separate printing plates. The printed page
will carry perfectly overlapped impressions
from the two printing plates. It's similar to
how to make a 4-color [CMYK] print run,
but instead of 4 colors, there are only two,
and both of them are black ! OK, they can
be warm black and cool black if desired to
print cool shadows and warm upper tones.

That is WHY duotone is called DUOtone :-)

If the above sounds very similar to HDR in
digital photography, then you understood
the explanation very well !

Soooooo .... the image below, which is in
MONOchrome is actually a true duotone ...
cuz it's an HDR image, as needed for the
crazy DR of such subject scenes. The HDR
process is just the digital child of duotone
offset printing :-)

.