Conditional expressions in Apply Image

[dmstraker]

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?

[v_kyr]

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.

[dmstraker]

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).

[v_kyr]

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 (?).

• Clamping in graphics

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 .

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 -->)

 

[Max P]

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

 

[John Rostron]

@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