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Implement sRGB color conversion (#510)

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* Add sRGB -> RGB conversion before resize

* Add clamping for color space conversions

* Clip for demultiplication as well

* Fixing linear <-> srgb conversion

* Update benchmark

* Decouple srgb calculations

* Generate lookup tables

* Update src/codecs/resize/options.tsx

* Defaulting on, renaming, removing redundant state
This commit is contained in:
Surma
2019-03-12 14:09:35 +00:00
committed by Jake Archibald
parent 496896e36e
commit bf4d4b78cb
13 changed files with 157 additions and 36 deletions
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60
codecs/resize/src/lib.rs
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@@ -9,6 +9,9 @@ use resize::Pixel::RGBA;
use resize::Type;
use wasm_bindgen::prelude::*;
mod srgb;
use srgb::Clamp;
cfg_if! {
// When the `wee_alloc` feature is enabled, use `wee_alloc` as the global
// allocator.
@@ -19,6 +22,39 @@ cfg_if! {
}
}
include!("./lut.inc");
// If `with_space_conversion` is true, this function returns 2 functions that
// convert from sRGB to linear RGB and vice versa. If `with_space_conversion` is
// false, the 2 functions returned do nothing.
fn converter_funcs(with_space_conversion: bool) -> ((fn(u8) -> f32), (fn(f32) -> u8)) {
if with_space_conversion {
(
|v| SRGB_TO_LINEAR_LUT[v as usize] * 255.0,
|v| (LINEAR_TO_SRGB_LUT[v as usize] * 255.0) as u8,
)
} else {
(|v| v as f32, |v| v as u8)
}
}
// If `with_alpha_premultiplication` is true, this function returns a function
// that premultiply the alpha channel with the given channel value and another
// function that reverses that process. If `with_alpha_premultiplication` is
// false, the functions just return the channel value.
fn alpha_multiplier_funcs(
with_alpha_premultiplication: bool,
) -> ((fn(f32, u8) -> u8), (fn(u8, u8) -> f32)) {
if with_alpha_premultiplication {
(
|v, a| (v * (a as f32) / 255.0) as u8,
|v, a| (v as f32) * 255.0 / (a as f32).clamp(0.0, 255.0),
)
} else {
(|v, _a| v as u8, |v, _a| v as f32)
}
}
#[wasm_bindgen]
#[no_mangle]
pub fn resize(
@@ -29,6 +65,7 @@ pub fn resize(
output_height: usize,
typ_idx: usize,
premultiply: bool,
color_space_conversion: bool,
) -> Vec<u8> {
let typ = match typ_idx {
0 => Type::Triangle,
@@ -40,12 +77,16 @@ pub fn resize(
let num_input_pixels = input_width * input_height;
let num_output_pixels = output_width * output_height;
if premultiply {
let (to_linear, to_color_space) = converter_funcs(color_space_conversion);
let (premultiplier, demultiplier) = alpha_multiplier_funcs(premultiply);
// If both options are false, there is no preprocessing on the pixel valus
// and we can skip the loop.
if premultiply || color_space_conversion {
for i in 0..num_input_pixels {
for j in 0..3 {
input_image[4 * i + j] = ((input_image[4 * i + j] as f32)
* (input_image[4 * i + 3] as f32)
/ 255.0) as u8;
input_image[4 * i + j] =
premultiplier(to_linear(input_image[4 * i + j]), input_image[4 * i + 3]);
}
}
}
@@ -62,15 +103,16 @@ pub fn resize(
output_image.resize(num_output_pixels * 4, 0);
resizer.resize(input_image.as_slice(), output_image.as_mut_slice());
if premultiply {
if premultiply || color_space_conversion {
for i in 0..num_output_pixels {
for j in 0..3 {
// We don’t need to worry about division by zero, as division by zero
// is well-defined on floats to return `±Inf`. ±Inf is converted to 0
// is well-defined on floats to return ±Inf. ±Inf is converted to 0
// when casting to integers.
output_image[4 * i + j] = ((output_image[4 * i + j] as f32) * 255.0
/ (output_image[4 * i + 3] as f32))
as u8;
output_image[4 * i + j] = to_color_space(demultiplier(
output_image[4 * i + j],
output_image[4 * i + 3],
));
}
}
}