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I've been tinkering with conditional expressions in Apply Image. Ideally you'd do something like (conditional-expression?A:B) so if conditional-expression (eg x>0.5) evaluates as true then the result is A otherwise B.

But they are not natural, so my current thinking is:

roundup(clamp(expression,0,1))

If expression evaluates as negative, then the result is 0 otherwise 1 (including if it is >1), so you then multiply the whole thing by what you want to actually end up with. The 'else' alternative would be found by adding a similar term with the expression reversed.

eg. DR=roundup(clamp(SR-0.5,0,1))*SG+roundup(clamp(0.5-SR,0,1))*SB

This should set red pixels to equal to green pixel if the red pixel < 0.5, otherwise it should be blue.

This, for example, lets you play with DIY blend modes which flip formula either side of 0.5.

Untidy, I know. Does it make sense? Any improvements?


Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast i9 Custom + Philips 40in 4K & Benq 23in; Surface Pro 4 i5; iPad Pro 11"

Favourite word: Aha. For me and for others.

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The conditional- or ternary operator is something often found in common prog-languages ...

  • condition ? value1 : value2      // where condition has to be a  boolean expression

  • variable = condition ? value1 : value2
  • int k = i == 10 ? 12 : 5; ... System.out.print(i == 10 ? 12 : 5);

Since I'm used to those things from programming it makes sense to me. - Though the way you can only apply/do such things at all in APh is primitive and poor. With some real scripting language support there should be instead much more things possible.


☛ Affinity Designer 1.8.3 ◆ Affinity Photo 1.8.3 ◆ OSX El Capitan

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7 hours ago, v_kyr said:

The conditional- or ternary operator is something often found in common prog-languages ...

  • condition ? value1 : value2      // where condition has to be a  boolean expression

  • 
    variable = condition ? value1 : value2
  • 
    int k = i == 10 ? 12 : 5; ... System.out.print(i == 10 ? 12 : 5);

Since I'm used to those things from programming it makes sense to me. - Though the way you can only apply/do such things at all in APh is primitive and poor. With some real scripting language support there should be instead much more things possible.

Yup. I was a programmer too. Assembler, C, ... And good scripting would be fab. Maybe in 2.0?

Meanwhile the round/clamp algorithm seems a feasible option (unless anyone cares to shoot in down in flames).


Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast i9 Custom + Philips 40in 4K & Benq 23in; Surface Pro 4 i5; iPad Pro 11"

Favourite word: Aha. For me and for others.

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36 minutes ago, dmstraker said:

Yup. I was a programmer too. Assembler, C, ... And good scripting would be fab. Maybe in 2.0?

Meanwhile the round/clamp algorithm seems a feasible option (unless anyone cares to shoot in down in flames).

Scripting in 2.0, maybe who knows (?).

Quote

In computer graphics, clamping is the process of limiting a position to an area. Unlike wrapping, clamping merely moves the point to the nearest available value. To put clamping into perspective, pseudocode for clamping is as follows:

Pseudocode (clamping):

function clamp(x, min, max):
    if (x < min) then
        x = min;
    else if (x > max) then
        x = max;
    return x;
end clamp

Uses

In general, clamping is used to restrict a value to a given range. For example, in OpenGL the glClearColor function takes four GLfloat values which are then 'clamped' to the range [0,1].

Y = clamp(X, 1, 5)
X Y
X < 1 1
1 1
1.5 1.5
2 2
3 3
4 4
5 5
X > 5 5

One of the many uses of clamping in computer graphics is the placing of a detail inside a polygon—for example, a bullet hole on a wall. It can also be used with wrapping to create a variety of effects. - (Note also the right side table there -->)

 


☛ Affinity Designer 1.8.3 ◆ Affinity Photo 1.8.3 ◆ OSX El Capitan

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Hi

 found this description

http://www.cplusplus.com/reference/cmath/round/

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/round.xhtml

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/clamp.xhtml

 

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@dmstraker,  I have used a similar formulation in Filter > Distort > Equations and it does work. I would also like to see some scripting available in Photo.

John

 


Windows 10, Affinity Photo 1.8,5 Designer 1.8.5 and Publisher 1.8.5 (mainly Photo), now ex-Adobe CC

CPU: AMD A6-3670. RAM: 16 GB DDR3 @ 666MHz, Graphics: 2047MB NVIDIA GeForce GT 630

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