diff --git a/src/standalone_srgb_antialiasing_experiments.c b/src/standalone_srgb_antialiasing_experiments.c
index 1928066..bd08c6d 100644
--- a/src/standalone_srgb_antialiasing_experiments.c
+++ b/src/standalone_srgb_antialiasing_experiments.c
@@ -717,19 +717,23 @@ static GLuint test3_texture = 0;
 #define       CIRCLE5_X 6.f
 #define       CIRCLE5_Y 6.f
 #define       CIRCLE5_SIDE 12
-static GLuint circle5_texture  = 0;
+static GLuint circle5_texture = 0;
 
 #define       CIRCLE25_RADIUS 25.f
 #define       CIRCLE25_X 30.f
 #define       CIRCLE25_Y 30.f
 #define       CIRCLE25_SIDE 60
-static GLuint circle25_texture  = 0;
+static GLuint circle25_texture = 0;
 
 #define       CIRCLE125_RADIUS 125.f
 #define       CIRCLE125_X 150.f
 #define       CIRCLE125_Y 150.f
 #define       CIRCLE125_SIDE 300
-static GLuint circle125_texture  = 0;
+static GLuint circle125_texture = 0;
+
+
+#define       CALIBRATION_SIDE 120
+static GLuint calibration_texture = 0;
 
 
 static void
@@ -919,6 +923,50 @@ opengl_render_init(void){
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
   }
   
+  //- calibration texture
+  {
+    U8 buf[CALIBRATION_SIDE*CALIBRATION_SIDE] = {0};
+    // checkerboards
+    for (U32 x = 0; x < (CALIBRATION_SIDE/2); x += 1){
+      for (U32 y = 0; y < (CALIBRATION_SIDE/2); y += 1){
+        B32 b = (((x + y)&1) == 1);
+        U8 c = b?255:0;
+        buf[x + y*CALIBRATION_SIDE] = c;
+        buf[x + (CALIBRATION_SIDE/2) + (y + (CALIBRATION_SIDE/2))*CALIBRATION_SIDE] = c;
+      }
+    }
+    // (1/2) gray srgb
+    for (U32 x = 0; x < (CALIBRATION_SIDE/2); x += 1){
+      for (U32 y = 0; y < (CALIBRATION_SIDE/2); y += 1){
+        buf[x + (CALIBRATION_SIDE/2) + y*CALIBRATION_SIDE] = 128;
+      }
+    }
+    // (1/2) gray linear
+    for (U32 x = 0; x < (CALIBRATION_SIDE/2); x += 1){
+      for (U32 y = 0; y < (CALIBRATION_SIDE/2); y += 1){
+        buf[x + (y + (CALIBRATION_SIDE/2))*CALIBRATION_SIDE] = 186;
+      }
+    }
+    
+    U8 img[CALIBRATION_SIDE*CALIBRATION_SIDE*3] = {0};
+    for (U32 i = 0; i < CALIBRATION_SIDE*CALIBRATION_SIDE; i += 1){
+      U8 c = buf[i];
+      img[i*3 + 0] = c;
+      img[i*3 + 1] = c;
+      img[i*3 + 2] = c;
+    }
+    
+    glGenTextures(1, &calibration_texture);
+    glBindTexture(GL_TEXTURE_2D, calibration_texture);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, CALIBRATION_SIDE, CALIBRATION_SIDE, 0,
+                 GL_RGB, GL_UNSIGNED_BYTE, img);
+    
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+  }
+  
   //- check for setup errors
   if (glGetError() != 0){
     error_message("error in opengl renderer initialization");
@@ -1091,6 +1139,9 @@ WinMain(HINSTANCE hInstance,
     F32 test7_y = graphics_h - 480.f;
     F32 test8_y = graphics_h - 800.f;
     
+    F32 calib_y = graphics_h - 10.f;
+    F32 calib_x = 10.f;
+    
     // render to canvas frame buffer
     {
       glBindFramebuffer(GL_FRAMEBUFFER, canvas_framebuffer);
@@ -1593,6 +1644,31 @@ WinMain(HINSTANCE hInstance,
             }
           }
         }
+        
+        // 9: color calibration blocks
+        if (test_idx == 0){
+          F32 y1 = calib_y;
+          F32 y0 = calib_y - CALIBRATION_SIDE;
+          F32 x0 = calib_x;
+          F32 x1 = calib_x + CALIBRATION_SIDE;
+          
+          Vertex v[6];
+          v[0].px  = x0;   v[0].py  = y0;
+          v[0].uvx = 0.f;  v[0].uvy = 0.f;
+          v[1].px  = x0;   v[1].py  = y1;
+          v[1].uvx = 0.f;  v[1].uvy = 1.f;
+          v[2].px  = x1;   v[2].py  = y0;
+          v[2].uvx = 1.f;  v[2].uvy = 0.f;
+          v[3].px  = x0;   v[3].py  = y1;
+          v[3].uvx = 0.f;  v[3].uvy = 1.f;
+          v[4].px  = x1;   v[4].py  = y0;
+          v[4].uvx = 1.f;  v[4].uvy = 0.f;
+          v[5].px  = x1;   v[5].py  = y1;
+          v[5].uvx = 1.f;  v[5].uvy = 1.f;
+          
+          opengl_draw_texture_geometry(v, 6, calibration_texture);
+        }
+        
       }
       
     }