image/lib/src/filter/adjust_color.dart

import 'dart:math';
import 'dart:typed_data';

import '../color.dart';
import '../image.dart';
import '../internal/clamp.dart';

/// Adjust the color of the [src] image using various color transformations.
///
/// [blacks] defines the black level of the image, as a color.
///
/// [whites] defines the white level of the image, as a color.
///
/// [mids] defines the mid level of hte image, as a color.
///
/// [contrast] increases (> 1) / decreases (< 1) the contrast of the image by
/// pushing colors away/toward neutral gray, where at 0.0 the image is entirely
/// neutral gray (0 contrast), 1.0, the image is not adjusted and > 1.0 the
/// image increases contrast.
///
/// [saturation] increases (> 1) / decreases (< 1) the saturation of the image
/// by pushing colors away/toward their grayscale value, where 0.0 is grayscale
/// and 1.0 is the original image, and > 1.0 the image becomes more saturated.
///
/// [brightness] is a constant scalar of the image colors.  At 0 the image
/// is black, 1.0 unmodified, and > 1.0 the image becomes brighter.
///
/// [gamma] is an exponential scalar of the image colors.  At < 1.0 the image
/// becomes brighter, and > 1.0 the image becomes darker.  A [gamma] of 1/2.2
/// will convert the image colors to linear color space.
///
/// [exposure] is an exponential scalar of the image as rgb/// pow(2, exposure).
/// At 0, the image is unmodified; as the exposure increases, the image
/// brightens.
///
/// [hue] shifts the hue component of the image colors in degrees.  A [hue] of
/// 0 will have no affect, and a [hue] of 45 will shift the hue of all colors
/// by 45 degrees.
///
/// [amount] controls how much affect this filter has on the [src] image, where
/// 0.0 has no effect and 1.0 has full effect.
Image adjustColor(Image src,
   {int blacks,
    int whites,
    int mids,
    num contrast,
    num saturation,
    num brightness,
    num gamma,
    num exposure,
    num hue,
    num amount}) {
  if (amount == 0.0) {
    return src;
  }

  const DEG_TO_RAD = 0.0174532925;
  const avgLumR = 0.5;
  const avgLumG = 0.5;
  const avgLumB = 0.5;
  const lumCoeffR = 0.2125;
  const lumCoeffG = 0.7154;
  const lumCoeffB = 0.0721;

  num br, bg, bb;
  num wr, wg, wb;
  num mr, mg, mb;
  if (blacks != null || whites != null || mids != null) {
    br = blacks != null ? getRed(blacks) / 255.0 : 0.0;
    bg = blacks != null ? getGreen(blacks) / 255.0 : 0.0;
    bb = blacks != null ? getBlue(blacks) / 255.0 : 0.0;

    wr = whites != null ? getRed(whites) / 255.0 : 1.0;
    wg = whites != null ? getGreen(whites) / 255.0 : 1.0;
    wb = whites != null ? getBlue(whites) / 255.0 : 1.0;

    mr = mids != null ? getRed(mids) / 255.0 : 0.5;
    mg = mids != null ? getGreen(mids) / 255.0 : 0.5;
    mb = mids != null ? getBlue(mids) / 255.0 : 0.5;

    mr = 1.0 / (1.0 + 2.0 * (mr - 0.5));
    mg = 1.0 / (1.0 + 2.0 * (mg - 0.5));
    mb = 1.0 / (1.0 + 2.0 * (mb - 0.5));
  }

  num invSaturation = saturation != null ? 1.0 - saturation : 0.0;
  num invContrast = contrast != null ? 1.0 - contrast : 0.0;

  if (exposure != null) {
    exposure = pow(2.0, exposure);
  }

  num hueR;
  num hueG;
  num hueB;
  if (hue != null) {
    hue *= DEG_TO_RAD;
    var s = sin(hue);
    var c = cos(hue);

    hueR = (2.0 * c) / 3.0;
    hueG = (-sqrt(3.0) * s - c) / 3.0;
    hueB = ((sqrt(3.0) * s - c) + 1.0) / 3.0;
  }

  var invAmount = amount != null ? 1.0 - amount : 0.0;

  Uint8List pixels = src.getBytes();
  for (int i = 0, len = pixels.length; i < len; i += 4) {
    num or = pixels[i] / 255.0;
    num og = pixels[i + 1] / 255.0;
    num ob = pixels[i + 2] / 255.0;

    num r = or;
    num g = og;
    num b = ob;

    if (br != null) {
      r = pow((r + br) * wr, mr);
      g = pow((g + bg) * wg, mg);
      b = pow((b + bb) * wb, mb);
    }

    if (brightness != null && brightness != 1.0) {
      r *= brightness;
      g *= brightness;
      b *= brightness;
    }

    if (saturation != null) {
      num lum = r * lumCoeffR + g * lumCoeffG + b * lumCoeffB;

      r = lum * invSaturation + r * saturation;
      g = lum * invSaturation + g * saturation;
      b = lum * invSaturation + b * saturation;
    }

    if (contrast != null) {
      r = avgLumR * invContrast + r * contrast;
      g = avgLumG * invContrast + g * contrast;
      b = avgLumB * invContrast + b * contrast;
    }

    if (gamma != null) {
      r = pow(r, gamma);
      g = pow(g, gamma);
      b = pow(b, gamma);
    }

    if (exposure != null) {
      r = r * exposure;
      g = g * exposure;
      b = b * exposure;
    }

    if (hue != null && hue != 0.0) {
      num hr = r * hueR + g * hueG + b * hueB;
      num hg = r * hueB + g * hueR + b * hueG;
      num hb = r * hueG + g * hueB + b * hueR;

      r = hr;
      g = hg;
      b = hb;
    }

    if (amount != null) {
      r = r * amount + or * invAmount;
      g = g * amount + og * invAmount;
      b = b * amount + ob * invAmount;
    }

    pixels[i] = clamp255((r * 255.0).toInt());
    pixels[i + 1] = clamp255((g * 255.0).toInt());
    pixels[i + 2] = clamp255((b * 255.0).toInt());
  }

  return src;
}