New!! - Bleach Bypass filter

[WorBry]

Thanks for your comments. All suggestions for improvement are most welcome.

Originally Posted by Gavino

Are the formulae for Additive and Subtractive correct?

For sure, the formulae per se are 'correct'.

Note that the opacity is only applied on one branch of the conditionals. That doesn't matter for Lighten and Darken, since the result is unchanged, but not for Additive and Subtractive - is this intended? Should it not be
(BLMode=="Additive") ? "x y + 255 > 255 x y + ? "+String(Opac)+" * x 1 "+String(Opac)+" - * + " etc

For the Opacity component of the mt_lutxy expression strings, I took the same as approach as Didee's earlier Hardlight functions:

http://forum.doom9.org/showpost.php?...32&postcount=2

And taking, for example, 'Additive':

(x + y ) > 255 ? 255 : (( x + y) * "+String(Opac)+" ) + (x * (1 - "+String(Opac)+" ))

....seems right to me and mt_polish (using a arbitary value instead of "+String(Opac)+" ) literally translates this to:

x y + 255 > 255 x y + "+String(Opac)+"  * x 1 "+String(Opac)+"  - * + ?

i.e. puts the ? ('If' condition) at the end of the string (stack?), which is how it is now in Blend_MT.

Reverse translation (mt_infix) of:

"x y + 255 > 255 x y + ? "+String(Opac)+" * x 1 "+String(Opac)+" - * + "

literally gives:

((((x + y) > 255 )) ? 255 : (x + y)) * "+String(Opac)+" ) + (x * (1 - "+String(Opac)+" )))

Which seems to be the same thing. Both '?' options work and give the same result, so I am not sure, which is the 'more correct' ?

I think it would make the formulae more readable and checkable if you defined the opacity expressions as variables, eg
Opacity = String(Opac)+" * x 1 "+String(Opac)+" - * + "
instead of repeating them everywhere.

Yes, I've been thinking of ways to cut down on the repetition, and will have a look at that, bearing in mind that there are six opacity determinants in all (Opac, Opac1, Opac2, SOpac, SOpac1, SOpac2).

I did at one point (posts #10 and #11) consider applying the blend opacity through a second mt_lutxy expression, but would that (obviously) would mean two lut calcs (each with their own rounding errors) instead of one, and make it more difficult to work in separate opacity determinants for <128 and >128 with the Hardlight, Softlight and Overlay modes.

Also, if you call the function with an unrecognised BLMode, it gives the error "I don't know what Bl1Expr means".
Better would be to replace the final Bl1Expr in the code above with something like
Assert(false, "Invalid BLMode String")

Quite agree. Added it. Thanks.