diff --git a/Makefile b/Makefile
index b85a7cb..652c1e2 100644
--- a/Makefile
+++ b/Makefile
@@ -4,6 +4,7 @@ include base.mk
 include common.mk
 include headers.mk
 
+OPT = -O2
 MAKEFILE_PATH := $(patsubst %/,%,$(dir $(abspath $(firstword $(MAKEFILE_LIST)))))
 CFLAGS += -I$(MAKEFILE_PATH)
 LIB ?= $(MAKEFILE_PATH)
diff --git a/example/example.mk b/example/example.mk
index 05f3985..05728ed 100644
--- a/example/example.mk
+++ b/example/example.mk
@@ -216,7 +216,8 @@ WIFFLE_SCREEN_SPACE_OBJ = \
 	holly/region_array.o \
 	holly/background.o \
 	holly/ta_fifo_polygon_converter.o \
-	sh7091/serial.o
+	sh7091/serial.o \
+	sobel.o
 
 example/wiffle_screen_space.elf: LDSCRIPT = $(LIB)/main.lds
 example/wiffle_screen_space.elf: $(START_OBJ) $(WIFFLE_SCREEN_SPACE_OBJ)
diff --git a/example/wiffle_screen_space.cpp b/example/wiffle_screen_space.cpp
index c6264eb..bbc6664 100644
--- a/example/wiffle_screen_space.cpp
+++ b/example/wiffle_screen_space.cpp
@@ -20,6 +20,8 @@
 #include "geometry/wiffle.hpp"
 #include "math/vec4.hpp"
 
+void convolve(uint32_t * in, uint32_t * out);
+
 constexpr float half_degree = 0.01745329f / 2;
 
 #define MODEL wiffle
@@ -170,6 +172,9 @@ void transform(ta_parameter_writer& parameter,
 uint32_t ta_parameter_buf[((32 * 8192) + 32) / 4]
 __attribute__((aligned(32)));
 
+uint32_t inbuf[640 * 480];
+uint32_t outbuf[640 * 480];
+
 void main()
 {
   video_output::set_mode_vga();
@@ -270,13 +275,17 @@ void main()
                        bytes_per_pixel);
     core_wait_end_of_render_video();
 
+    uint32_t * in = (uint32_t *)&texture_memory64[texture_memory_alloc.texture.start / 4];
 
 
+
+    uint32_t * out = (uint32_t *)&texture_memory32[texture_memory_alloc.framebuffer[0].start / 4];
+    convolve(in, out);
+
     while (!spg_status::vsync(holly.SPG_STATUS));
     holly.FB_R_SOF1 = texture_memory_alloc.framebuffer[0].start;
     while (spg_status::vsync(holly.SPG_STATUS));
 
-    /*
     holly.FB_R_CTRL = fb_r_ctrl::vclk_div::pclk_vclk_1
                     | fb_r_ctrl::fb_depth::_0888_rgb_32bit
                     | fb_r_ctrl::fb_enable;
@@ -284,9 +293,7 @@ void main()
     holly.FB_R_SIZE = fb_r_size::fb_modulus(1)
                     | fb_r_size::fb_y_size(480 - 3)
                     | fb_r_size::fb_x_size((640 * 32) / 32 - 1);
-    */
 
-    //theta += half_degree;
-    break;
+    theta += half_degree;
   }
 }
diff --git a/holly/texture_memory_alloc3.hpp b/holly/texture_memory_alloc3.hpp
index 7479140..fcd1c92 100644
--- a/holly/texture_memory_alloc3.hpp
+++ b/holly/texture_memory_alloc3.hpp
@@ -30,8 +30,10 @@ constexpr texture_memory_alloc texture_memory_alloc = {
   .background         = {{0x07'ffe0, 0x08'0000}, {0x47'ffe0, 0x48'0000}},
   .object_list        = {{0x08'0000, 0x0f'ffe0}, {0x48'0000, 0x4f'ffe0}}, // ~122880 object list pointers
   .region_array       = {{0x10'0000, 0x11'0000}, {0x50'0000, 0x51'0000}}, // ~9 render passes
-  .framebuffer        = {{0x11'0000, 0x1b'8c00}, {0x51'0000, 0x5b'8c00}}, // 720x480*2bpp
+  //.framebuffer        = {{0x11'0000, 0x1b'8c00}, {0x51'0000, 0x5b'8c00}}, // 720x480*2
+  .framebuffer        = {{0x11'0000, 0x23'c000}, {0x51'0000, 0x63'c000}}, // 640x480*4
 
   // 64-bit addresses
-  .texture = {0x37'1800, 0x80'0000}
+  //.texture = {0x37'1800, 0x80'0000}
+  .texture = {0x57'1800, 0x80'0000}
 };
diff --git a/sobel.cpp b/sobel.cpp
new file mode 100644
index 0000000..b15995f
--- /dev/null
+++ b/sobel.cpp
@@ -0,0 +1,102 @@
+#include <stdint.h>
+
+int clamp255(float v)
+{
+  int n = (int)v;
+  if (n < 0)
+    return 0;
+  if (n > 255)
+    return 255;
+  return n;
+}
+
+uint32_t getpx(uint32_t * buf, int x, int y)
+{
+  if (x < 0)
+    x = 0;
+  if (y < 0)
+    y = 0;
+  if (x >= 640)
+    x = 640 - 1;
+  if (y >= 480)
+    y = 480 - 1;
+  return buf[y * 640 + x];
+}
+
+float multiply(uint32_t * buf, int x, int y, float weight)
+{
+  uint32_t color = getpx(buf, x, y);
+  int b = color & 0xff;
+  color >>= 8;
+  int g = color & 0xff;
+  color >>= 8;
+  int r = color & 0xff;
+  color >>= 8;
+  int a = color;
+
+  float luminance = (float)(r + g + b + a) * 0.25;
+  return luminance * (float)weight;
+}
+
+float kernel(uint32_t * buf, const float * weights, int x, int y)
+{
+  float c = 0;
+  c += multiply(buf, x - 1, y - 1, weights[0]);
+  c += multiply(buf, x    , y - 1, weights[1]);
+  c += multiply(buf, x + 1, y - 1, weights[2]);
+
+  c += multiply(buf, x - 1, y    , weights[3]);
+  c += multiply(buf, x    , y    , weights[4]);
+  c += multiply(buf, x + 1, y    , weights[5]);
+
+  c += multiply(buf, x - 1, y + 1, weights[6]);
+  c += multiply(buf, x    , y + 1, weights[7]);
+  c += multiply(buf, x + 1, y + 1, weights[8]);
+
+  return c;
+}
+
+const float gx[] = {
+    1, 0, -1,
+    2, 0, -2,
+    1, 0, -1,
+};
+
+const float gy[] = {
+    1, 2, 1,
+    0, 0, 0,
+    -1, -2, -1,
+};
+
+void convolve(uint32_t * in, uint32_t * out)
+{
+  for (int y = 0; y < 480; y++) {
+    for (int x = 0; x < 640; x++) {
+      float vx = kernel(in, gx, x, y);
+      float vy = kernel(in, gy, x, y);
+      float c = vx * vx + vy * vy;
+      int d = c > 100.f ? 0 : 1;
+      uint32_t color = in[y * 640 + x];
+
+      int b = color & 0xff;
+      color >>= 8;
+      int g = color & 0xff;
+      color >>= 8;
+      int r = color & 0xff;
+      color >>= 8;
+      int a = color;
+
+      uint32_t color_out = 0;
+
+      //color_out |= (a * d);
+      //color_out <<= 8;
+      color_out |= (r * d);
+      color_out <<= 8;
+      color_out |= (g * d);
+      color_out <<= 8;
+      color_out |= (b * d);
+
+      out[y * 640 + x] = color_out;
+    }
+  }
+}