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Fix high contrast render in midnight mode #197

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Fix high contrast render in midnight mode #197

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cf19ccc
Fix high contrast render in midnight mode
Atreyagaurav Mar 3, 2023
61ce548
Add hue contribution of background color to inverted midnight mode
Apr 4, 2023
777530e
Fix comment
Apr 4, 2023
ba76d7c
Merge pull request #1 from smithzvk/master
Atreyagaurav Apr 4, 2023
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128 changes: 78 additions & 50 deletions server/epdfinfo.c
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Original file line number Diff line number Diff line change
Expand Up @@ -473,15 +473,19 @@ image_recolor (cairo_surface_t * surface, const PopplerColor * fg,
{
/* Performs one of two kinds of image recoloring depending on the value of usecolors:

1 -> uses a representation of a rgb color as follows:
- a lightness scalar (between 0,1), which is a weighted average of r, g, b,
- a hue vector, which indicates a radian direction from the grey axis,
inside the equal lightness plane.
- a saturation scalar between 0,1. It is 0 when grey, 1 when the color is
in the boundary of the rgb cube.

2 -> Invert the perceived lightness in the image while maintaining hue.
*/
1 -> Bg-Fg Interpolation: maps source document colors to colors
interpolated between the background and foreground values in
pdf-view-midnight-colors via the lightness of the source color. This
discards hue information but allows you to fit your color theme
perfectly.

2 -> Hue-Preserving interpolation: same as above, similar to above, but
attempts to preserve hue while still respecting the background and
foreground colors. This is done by matching source document white and
black to the specified background and foreground as above, but mixes
hue/saturation with the background color. This preserves hue but is
more expensive.
*/

const unsigned int page_width = cairo_image_surface_get_width (surface);
const unsigned int page_height = cairo_image_surface_get_height (surface);
Expand Down Expand Up @@ -509,37 +513,27 @@ image_recolor (cairo_surface_t * surface, const PopplerColor * fg,
.b = rgb_bg.b - rgb_fg.b
};

/* The Oklab transform is expensive, precompute white->black and have a single
entry cache to speed up computation */
struct color white = {.r = 1.0, .g = 1.0, .b = 1.0};
struct color black = {.r = 0.0, .g = 0.0, .b = 0.0};
struct color precomputed_rgb = white;
struct color precomputed_inv_rgb = black;

unsigned int y;
for (y = 0; y < page_height * rowstride; y += rowstride)
switch (usecolors)
{
unsigned char *data = image + y;
case 0:
break;
case 1:
{
unsigned int y;
for (y = 0; y < page_height * rowstride; y += rowstride)
{
unsigned char *data = image + y;

unsigned int x;
for (x = 0; x < page_width; x++, data += 4)
{
/* Careful. data color components blue, green, red. */
struct color rgb = {
.r = (double) data[2] / 256.,
.g = (double) data[1] / 256.,
.b = (double) data[0] / 256.
};

switch (usecolors)
{
case 0:
/* No image recoloring requested. Do nothing in this case.
Should never be called as we should never call with unless
usecolors != 0. */
break;
case 1:
unsigned int x;
for (x = 0; x < page_width; x++, data += 4)
{
/* Careful. data color components blue, green, red. */
struct color rgb = {
.r = (double) data[2] / 256.,
.g = (double) data[1] / 256.,
.b = (double) data[0] / 256.
};

/* Linear interpolation between bg and fg based on the
perceptual lightness measure l */
/* compute h, s, l data */
Expand All @@ -554,14 +548,44 @@ image_recolor (cairo_surface_t * surface, const PopplerColor * fg,
data[0] =
(unsigned char) round (255. * (l * rgb_diff.b + rgb_fg.b));
}
break;
case 2:
}
}
break;
case 2:
{
/* If using the Oklab transform, it is relatively expensive. Precompute
white->background and black->foreground and have a single entry cache to
speed up computation */
const struct color white = {.r = 1.0, .g = 1.0, .b = 1.0};
struct color precomputed_rgb = white;
struct color precomputed_inv_rgb = rgb_bg;

/* Must match the transformation of colors below. */
struct color oklab_fg = rgb2oklab(rgb_fg);
struct color oklab_bg = rgb2oklab(rgb_bg);

const double oklab_diff_l = oklab_fg.l - oklab_bg.l;

unsigned int y;
for (y = 0; y < page_height * rowstride; y += rowstride)
{
unsigned char *data = image + y;

unsigned int x;
for (x = 0; x < page_width; x++, data += 4)
{
/* Careful. data color components blue, green, red. */
struct color rgb = {
.r = (double) data[2] / 256.,
.g = (double) data[1] / 256.,
.b = (double) data[0] / 256.
};

/* Convert to Oklab coordinates, invert perceived lightness,
convert back to RGB. */
if (color_equal(white, rgb))
{
rgb = black;
rgb = rgb_bg;
}
else if (color_equal(precomputed_rgb, rgb))
{
Expand All @@ -572,12 +596,16 @@ image_recolor (cairo_surface_t * surface, const PopplerColor * fg,
struct color oklab = rgb2oklab(rgb);
precomputed_rgb = rgb;

/* Gamma correction. Shouldn't be necessary, but colors
* 'feel' too dark and fonts too thin otherwise. */
oklab.l = pow(oklab.l, 1.8);
/* Invert the perceived lightness, and scales it */
double l = oklab.l;
double inv_l = 1.0 - l;
oklab.l = oklab_bg.l + oklab_diff_l * inv_l;

/* Invert the perceived lightness */
oklab.l = 1.0 - oklab.l;
/* Have a and b parameters (which encode hue and saturation)
start at the background value and interpolate up to
foreground */
oklab.a = (oklab.a + oklab_bg.a * l + oklab_fg.a * inv_l);
oklab.b = (oklab.b + oklab_bg.b * l + oklab_fg.b * inv_l);

rgb = oklab2rgb(oklab);

Expand All @@ -588,11 +616,11 @@ image_recolor (cairo_surface_t * surface, const PopplerColor * fg,
data[1] = (unsigned char) round(255. * rgb.g);
data[0] = (unsigned char) round(255. * rgb.b);
}
break;
default:
internal_error ("image_recolor switch fell through");
}
}
}
}
break;
default:
internal_error ("image_recolor switch fell through");
}
}

Expand Down