1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
|
/* VideoSwitcherSimpleLuminanceToRB8_FormattingShader.frag.txt -- Luminance output formatter
*
* This shader converts a HDR luminance texture into a RGBA8 8bpc framebuffer
* image, suitable for display with the Xiangru Li et al. "VideoSwitcher" video
* attenuator device. The "Simple" converter uses a closed-form solution to
* map luminance to (Red,Blue) channel output values.
*
* It expects the luminance image data in the red channel of the texture,
* with values ranging from 0.0 - 1.0, remaps it into the bpc bit data range
* of the device of 16 bpc, then converts the 16 bit integral luminance index
* value into proper red, blue drive pixel output.
*
* The green and alpha channels are unused and simply set to a constant zero value.
*
* This shader is intended for use as a plugin for the 'FinalOutputFormattingBlit'
* chain of the Psychtoolbox-3 imaging pipeline.
*
* (c)2007, 2008 by Mario Kleiner, part of PTB-3, licensed to you under MIT license.
* See file License.txt in the Psychtoolbox root folder for the license.
*
*/
#extension GL_ARB_texture_rectangle : enable
/* The input Image - Usually from texture unit 0: */
uniform sampler2DRect Image;
/* The btrr calibration value: Blue-To-Red-Ratio from calibration: */
uniform float btrr;
/* btrr + 1, passed from host to save a floating point addition.: */
uniform float btrrPlusOne;
/* (btrr + 1) / btrr, passed from host to save addition and division.: */
uniform float btrrFractionTerm;
/* Declare external function for luminance color conversion: */
float icmTransformColor1(float incolor);
void main()
{
vec4 outcolor = vec4(0.0);
/* Retrieve HDR/High precision input luminance value from RED channel: */
/* The same value is stored (replicated) in the GREEN and BLUE channels */
/* if this is a drawn luminance image, so choice of channel doesn't matter. */
/* We expect these values to be in 0.0 - 1.0 range. */
/* We add a small numerical 'epsilon' offset of 1e-7 to the fetched value. */
/* This is to account for small numerical differences between GPU's float */
/* storage format and CPU's double format. This is not strictly neccessary, */
/* but we do it to achieve identical results between GPU and CPU conversion */
/* to simplify validation/testing and intermix of CPU and GPU methods. */
float lum = texture2DRect(Image, gl_TexCoord[0].st).r + 0e-7;
/* Apply some color transformation (clamping, gamma correction etc.): */
lum = icmTransformColor1(lum);
/* Remap 'lum' from 0.0 - 1.0 range to range 0.0 - 255.0. */
lum = lum * 255.0;
/* First compute blue output channel: Value will be integral, clamped to [0; 255]: */
outcolor.b = min( 255.0, floor(btrrFractionTerm * lum) );
/* Compute remainder and compensate for that residual via red channel: */
outcolor.r = floor((btrrPlusOne * lum) - (outcolor.b * btrr) + 0.5);
/* Need to remap out.br values from range 0 - 255 to framebuffers uint8 */
/* output range of 0.0 - 1.0: */
outcolor.rb = outcolor.rb / 255.0;
/* Copy output pixel to RGBA8 fixed point framebuffer: */
gl_FragColor = outcolor;
}
|
