Re-definition of an already-defined function.

[digital-nomad-cheng]

Hi, thank you for you awesome work! I'm trying to use Halide to implement a color balance algorithms.
Here's my code:

Halide::Var x("x");
Halide::Var y("y");
Halide::Var c("c");

Halide::Func hist("hist");
Halide::Func cdf("cdf");
Halide::Func min_count("min_count");
Halide::Func max_count("max_count");
Halide::Func min_sum("min_sum");
Halide::Func max_sum("max_sum");

// 1. calculate histogram
hist(x, c) = 0.0f;
Halide::RDom r(0, input.width(), 0, input.height());
Halide::Expr value = Halide::cast<uint8_t>(Halide::clamp(input(r.x, r.y, c)*255.0f, 0.0f, 255.0f));
hist(value, c) += 1.0f;

// 2. calculate cumulative distribute function
cdf(x, c) = 0.0f;
Halide::RDom rcdf(0, 256);
cdf(rcdf.x+1, c) = cdf(rcdf.x, c) + hist(rcdf.x, c); 

// 3. calculate min, max threshold
const float s = 0.0265; // the parameter to adjust，it should be better below 0.1
Halide::Expr num_pixels = input.width() * input.height();
Halide::Expr min_threshold = num_pixels * s / 2;
Halide::Expr max_threshold = num_pixels * (1.0f - s / 2);

min_count(x, c) = 0.0f;
min_count(x, c) = Halide::select(cdf(x, c) < min_threshold, 1.0f, 0.0f);

max_count(x, c) = 0.0f;
max_count(x, c) = Halide::select(cdf(x, c) < max_threshold, 1.0f, 0.0f);

min_sum(c) = 0.0f;	
min_sum(c) = Halide::sum(min_count(rcdf.x, c));
max_sum(c) = 0.0f;
max_sum(c) = Halide::sum(max_count(rcdf.x, c));

// 4. adjust the over dark and over bright pixels
output(x, y, c) = Halide::clamp(input(x, y, c), min_sum(c)/255.0f, max_sum(c)/255.0f);

While compiling this code, I always got these warinings:

Warning: In update definition 0 of Func "min_count":
Update definition completely hides earlier definitions,  because all the arguments are pure, it contains no self-references,  and no reduction domain. This may be an accidental re-definition of  an already-defined function.
Warning: In update definition 0 of Func "max_count":
Update definition completely hides earlier definitions,  because all the arguments are pure, it contains no self-references,  and no reduction domain. This may be an accidental re-definition of  an already-defined function.
Warning: In update definition 0 of Func "min_sum":
Update definition completely hides earlier definitions,  because all the arguments are pure, it contains no self-references,  and no reduction domain. This may be an accidental re-definition of  an already-defined function.
Warning: In update definition 0 of Func "max_sum":
Update definition completely hides earlier definitions,  because all the arguments are pure, it contains no self-references,  and no reduction domain. This may be an accidental re-definition of  an already-defined function.

Can someone tell me, what's the meaning of these warnings?
My code couldn't get the right result, so I'm trying to locate the problems.

Again, appreciate your work.

[alexreinking]

So for these funcs:

min_sum(c) = 0.0f;	
min_sum(c) = Halide::sum(min_count(rcdf.x, c));
max_sum(c) = 0.0f;
max_sum(c) = Halide::sum(max_count(rcdf.x, c));

You probably meant to write:

min_sum(c) = 0.0f;	
min_sum(c) += min_count(rcdf.x, c);
max_sum(c) = 0.0f;
max_sum(c) += max_count(rcdf.x, c);

I'm not sure what you were trying to accomplish here:

min_count(x, c) = 0.0f;
min_count(x, c) = Halide::select(cdf(x, c) < min_threshold, 1.0f, 0.0f);

max_count(x, c) = 0.0f;
max_count(x, c) = Halide::select(cdf(x, c) < max_threshold, 1.0f, 0.0f);

But hopefully the hint above will clear things up (maybe you just don't need the = 0 stages). Definitely read through this tutorial, too: https://halide-lang.org/tutorials/tutorial_lesson_09_update_definitions.html