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View Full Version : FAUX HDR opengl ES 2.0 shader algorithm



sanchiski
04-20-2014, 07:55 AM
I'm trying to create a GLSL shader to produce the FAUX HDR effect also known as FAKE HDR, (not to confuse with normal HDR where 3 images with different exposures are combined). I need to create it in a single shader algorithm and not multiple shaders with different passes.

The idea is to achieve images such as in the next links, where the image has high local micro-contrast and intense colors, with mostly important a holo white aura around some edges.

Image Sample 1 (http://www.markgaler.com/wp-content/uploads/2011/11/Faux-HDR-ACR-2-AFTER1.jpg)

Image Sample 2 (http://media02.hongkiat.com/hdr-photography/Winter-Wonderland.jpg)

Image Sample 3 (http://davedicello.com/wp-content/uploads/2011/04/hallway-at-carrie-furnace.jpg)

From the steps on the next document I started to build the shader:

HDR steps documentation (http://www.cromwell-intl.com/3d/histogram/)

So far the next code is my result, the problem is that is really not showing anything near at all of the desired FAUX HDR result.

VERTEX SHADER:



varying vec2 v_texcoord;

void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
v_texcoord = gl_MultiTexCoord0.xy;
}


FRAGMENT SHADER:



varying vec2 v_texcoord;
uniform sampler2D texture;

vec3 rgb2hsv(vec3 c)
{
vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));

float d = q.x - min(q.w, q.y);
float e = 1.0e-10;
return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
}

vec3 hsv2rgb(vec3 c)
{
vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

void main()
{
vec4 color = texture2D(texture, v_texcoord);

vec3 hsv = rgb2hsv(color.rgb);

float intensity = hsv.z; // the third component holds the brightness

float log_factor = log(intensity + 1.0);

log_factor = exp(log_factor) - 1.0;

hsv.z = log_factor;

color.rgb = hsv2rgb(hsv);

gl_FragColor = color;
}