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Re: Custom Curves



> Four control points are not enough in certain cases.


Agreed.  I think that must have been a decision made in the interest of
simplifying operation of custom-curves in the days before a graphical user
interface.  With DUI things could be different.
Since the magic of custom curves happens in the Primaries boards you could
potentially have many, many more points.  The basic mechanism is
conceptually simple:  The DSP gets control information (black, lift, gamma,
curve settings, etc).  It then crunches on all the parameters and comes-up
with a transfer-curve that is written into a set of lookup tables.  If I
remember correctly the lookup tables are setup with 1024 levels (a nice
digital number)...  So, at least in theory, you could have that many control
points.  In practice, my guess is you could double the current number.  The
main constraint is how quickly the DSP can crunch on the parameters you are
sending it.    If enough folks think this is an issue I'm sure daVinci would
look into it.

> The range of the curve should exceed the present 0 to 100 limit.  This
>way you could get a strong white compression to emulate a print, for
>example.


I'm not sure how the firmware maps the 0 to 100 limits into what the lookup
table sees.  This would be a daVinci question.

>As far as the inability to have a normal curve and add a custom curve on
>top, you don't have to wait for the 2K.  Do your normal color balance,
>then turn on a power window and make the size larger than the picture
>area.  Put a custom curve inside the window, like a nice print like
>curve.  Now you have layered a custom curve on top of a normal black
>stretch type curve.


Neat !!!  I'm angry now.... I didn't think of that.  I should have.  My
punishment will be to go to Fry's Electronics and not buy anything.  :-(
To complete the Primaries board mechanism I described above... there are two
sets of lookup tables, yes, you guessed it:  inside and outside window.  So,
yes, you can have a normal gamma curve "outside" and a custom-curve
"inside".
Hmmm... I have to think about this... but I think that you could avoid
using-up your power window if your key input was available.  You'd just feed
like a full field of 50% luminance (or whatever) and key to that.  Force the
cursor "inside" and setup your custom curve.

-Martin





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