diff --git a/OverLua/docs/expression-evaluator.txt b/OverLua/docs/expression-evaluator.txt
index 2cb3ad7eb..1036aaf50 100644
--- a/OverLua/docs/expression-evaluator.txt
+++ b/OverLua/docs/expression-evaluator.txt
@@ -217,4 +217,10 @@ else return the third argument.
 Sample programs
 ---------------
 
-To be written. No functions in OverLua use the expression evaluator yet.
+For raster.pixel_value_map:
+
+"rand =t0 t0 =R t0 =G t0 =B"
+Create a field of random gray-values.
+
+"0 =R 1 G - =G"
+Zero out the red channel and invert the green channel.
diff --git a/OverLua/docs/overlua.txt b/OverLua/docs/overlua.txt
index e36b58656..d3492043c 100644
--- a/OverLua/docs/overlua.txt
+++ b/OverLua/docs/overlua.txt
@@ -188,6 +188,25 @@ The filter is one-dimensional, but is applied first horizontally and then
 vertically ovre the image to get the final image.
 
 
+raster.pixel_value_map(surface, expression)
+
+Map an expression over every pixel RGB value in the surface. Only works for
+ARGB32 and RGB24 surfaces.
+
+The expression is an RPN expression in the OverLua Expression Evaluator
+language, see expression-evaluator.txt for details.
+
+No additional functions are made available to the expression evaluator by
+this function.
+
+The following new registers are made available to the expression evaluator:
+  R  In range 0..1, red component. Input and output.
+  G  Ditto, for green component.
+  B  Ditto, for blue component.
+  X  X-coordinate of pixel being processed. Input only.
+  Y  Y-coordinate of pixel being processed. Input only.
+
+
 More filtering functions are planned, though no specifics yet.
 
 Wishes/suggestions are welcome, and so are patches to add more functions.
diff --git a/OverLua/docs/test3.lua b/OverLua/docs/test3.lua
index d36089865..1a53015fe 100644
--- a/OverLua/docs/test3.lua
+++ b/OverLua/docs/test3.lua
@@ -5,5 +5,10 @@ function render_frame(f, t)
 	--raster.separable_filter(surf, {-1, 3, -1}, 1) 
 	--raster.directional_blur(surf, t, t/10)
 	raster.radial_blur(surf, 200, 200, t/60)
+	raster.pixel_value_map(surf, "0 =R 1 G - =G")
 	f.overlay_cairo_surface(surf, 0, 0)
+	
+	surf = cairo.image_surface_create(200, 200, "rgb24")
+	raster.pixel_value_map(surf, "rand =t0 t0 =R t0 =G t0 =B")
+	f.overlay_cairo_surface(surf, 20, 20)
 end
diff --git a/OverLua/expression_engine.h b/OverLua/expression_engine.h
index 34a4da00d..442cbf844 100644
--- a/OverLua/expression_engine.h
+++ b/OverLua/expression_engine.h
@@ -105,6 +105,9 @@ namespace ExpressionEngine {
 
 		// Create a machine from a specification and a program source
 		Machine(const Specification &spec, const char *source);
+
+		// Create a blank machine
+		Machine() { }
 	};
 
 };
diff --git a/OverLua/raster_ops.cpp b/OverLua/raster_ops.cpp
index 91bced849..e5fabfc56 100644
--- a/OverLua/raster_ops.cpp
+++ b/OverLua/raster_ops.cpp
@@ -30,6 +30,7 @@
 #include <omp.h>
 #include <stdint.h>
 
+#include "expression_engine.h"
 #include "raster_ops.h"
 #include "../lua51/src/lauxlib.h"
 
@@ -686,6 +687,82 @@ static int separable_filter(lua_State *L)
 }
 
 
+static int pixel_value_map(lua_State *L)
+{
+	cairo_surface_t *surf = CheckSurface(L, 1);
+	const char *program = luaL_checkstring(L, 2);
+
+	// Set up engine specs
+	ExpressionEngine::Specification spec;
+	spec.registers.resize(5);
+	spec.registers[0] = "R";
+	spec.registers[1] = "G";
+	spec.registers[2] = "B";
+	spec.registers[3] = "X";
+	spec.registers[4] = "Y";
+
+	// Compile program
+	ExpressionEngine::Machine machine;
+	try {
+		machine = ExpressionEngine::Machine(spec, program);
+	}
+	catch (const char *e) {
+		// This is a parse error
+		luaL_error(L, "Error in expression program near\"%s\"", e);
+	}
+
+	// Init image
+	cairo_surface_flush(surf);
+	int width = cairo_image_surface_get_width(surf);
+	int height = cairo_image_surface_get_height(surf);
+	ptrdiff_t stride = (ptrdiff_t)cairo_image_surface_get_stride(surf);
+	unsigned char *data = cairo_image_surface_get_data(surf);
+	cairo_format_t format = cairo_image_surface_get_format(surf);
+
+	if (format == CAIRO_FORMAT_ARGB32) {
+		BaseImage<PixelFormat::cairo_argb32> img(width, height, stride, data);
+		for (int y = 0; y < height; y++) {
+			for (int x = 0; x < width; x++) {
+				PixelFormat::cairo_argb32 &p = img.Pixel(x, y);
+				machine.registers[0] = (double)p.R() / 255.0;
+				machine.registers[1] = (double)p.G() / 255.0;
+				machine.registers[2] = (double)p.B() / 255.0;
+				machine.registers[3] = x;
+				machine.registers[4] = y;
+				machine.Run();
+				p.R() = (uint8_t)(machine.registers[0] * 255);
+				p.G() = (uint8_t)(machine.registers[1] * 255);
+				p.B() = (uint8_t)(machine.registers[2] * 255);
+			}
+		}
+	}
+	else if (format == CAIRO_FORMAT_RGB24) {
+		BaseImage<PixelFormat::cairo_rgb24> img(width, height, stride, data);
+		for (int y = 0; y < height; y++) {
+			for (int x = 0; x < width; x++) {
+				PixelFormat::cairo_rgb24 &p = img.Pixel(x, y);
+				machine.registers[0] = (double)p.R() / 255.0;
+				machine.registers[1] = (double)p.G() / 255.0;
+				machine.registers[2] = (double)p.B() / 255.0;
+				machine.registers[3] = x;
+				machine.registers[4] = y;
+				machine.Run();
+				p.R() = (uint8_t)(machine.registers[0] * 255);
+				p.G() = (uint8_t)(machine.registers[1] * 255);
+				p.B() = (uint8_t)(machine.registers[2] * 255);
+			}
+		}
+	}
+	else {
+		luaL_error(L, "Unsupported pixel format");
+	}
+
+	cairo_surface_mark_dirty(surf);
+
+	return 0;
+}
+
+
 // Registration
 
 static luaL_Reg rasterlib[] = {
@@ -693,6 +770,7 @@ static luaL_Reg rasterlib[] = {
 	{"directional_blur", directional_blur}, {"radial_blur", radial_blur},
 	{"separable_filter", separable_filter},
 	{"invert", invert_image},
+	{"pixel_value_map", pixel_value_map},
 	{NULL, NULL}
 };