Optionally print debug information

build-number.txt

@@ -1 +1 @@
-562
+615

src/config.h

@@ -0,0 +1,21 @@
+#pragma once
+
+// Use 2D Floyd-Steinberg dithering. Uncomment to use simple line-wise
+// dithering.
+#define CONFIG_USE_2D_DITHERING
+
+// Use a primitive autoexposure by shifting each frames luminosity based on the
+// ratio of white to black pixels in the previous frames
+// #define CONFIG_USE_EXPOSURE_CORRECTION
+
+// Capture a frame when it is within this tolerance of 50% black pixels
+#define CONFIG_TOLERANCE        0.2
+
+// Wait this number of frames before a frame is eligible for beaing captured
+#define CONFIG_MIN_FRAMES       2
+
+// Maximum number of frames to wait. Capture even if it is not within tolerance.
+#define CONFIG_MAX_FRAMES       15
+
+// Print number of black pixels per captured frame
+// #define CONFIG_PRINT_EXPOSURE_DEBUG_INFORMATION

src/main.c

@@ -22,6 +22,24 @@ int main(void)
     extern uint8_t ImageBuffer[CAMERA_IMAGE_WIDTH * CAMERA_IMAGE_HEIGHT / 8];
     Print_Image(ImageBuffer, CAMERA_IMAGE_WIDTH, CAMERA_IMAGE_HEIGHT, 2);
 
+#ifdef CONFIG_PRINT_EXPOSURE_DEBUG_INFORMATION
+    char buffer[32] = "Finished after lines: ";
+    itoa(Camera_FinalFrameCount, buffer + strlen(buffer), 10);
+
+    Print_Text(buffer, &Arpegius_32);
+    Print_Text("Black pixel counts:", &Arpegius_32);
+    for(int i = 0; i < Camera_FinalFrameCount; i++)
+    {
+        if(i >= (int)(sizeof(Camera_BlackPixelCounts)
+            / sizeof(Camera_BlackPixelCounts[0])))
+        {
+            break;
+        }
+        itoa(Camera_BlackPixelCounts[i], buffer, 10);
+        Print_Text(buffer, &Arpegius_32);
+    }
+#endif
+
     LTP1245_FeedPaper(100);
 
     BMP_Save(ImageBuffer, CAMERA_IMAGE_WIDTH, CAMERA_IMAGE_HEIGHT);

src/main.h

@@ -16,6 +16,7 @@
 #include "font_arpegius_16.h"
 #include "font_arpegius_32.h"
 #include "bmp.h"
+#include "config.h"
 
 int main(void);
 

src/ov7670.c

@@ -126,12 +126,12 @@
 #define REG_HAECC2              0xa0
 #define REG_SCALING_PCLK_DELAY  0xa2
 #define REG_NT_CTRL             0xa4
-#define REG_BD50MAX             0xa5
+#define REG_AECGMAX             0xa5
-#define REG_HAECC3              0xa6
+#define REG_LPH                 0xa6
-#define REG_HAECC4              0xa7
+#define REG_UPL                 0xa7
-#define REG_HAECC5              0xa8
+#define REG_TPL                 0xa8
-#define REG_HAECC6              0xa9
+#define REG_TPH                 0xa9
-#define REG_HAECC7              0xaa
+#define REG_NALG                0xaa
 #define REG_BD60MAX             0xab
 #define REG_STR_OPT             0xac
 #define REG_STR_R               0xad
@@ -156,10 +156,13 @@ static volatile int FrameCount = 0;
 volatile int Camera_Captured = 0;
 static unsigned int BlackPixels = 0;
 
-#ifdef CAMERA_USE_EXPOSURE_CORRECTION
+#ifdef CONFIG_USE_EXPOSURE_CORRECTION
 static volatile int ExposureCorrection = 0;
 #endif
 
+volatile unsigned int Camera_BlackPixelCounts[] = {0};
+volatile int Camera_FinalFrameCount = -1;
+
 static uint8_t ReadRegister(uint8_t reg)
 {
     while(I2C1->SR2 & I2C_SR2_BUSY);
@@ -301,6 +304,24 @@ void Camera_Init(void)
     WriteRegister(REG_COM14, 0x18 | 1);
     WriteRegister(REG_SCALING_PCLK_DIV, 1);
 
+    // Set maximum gain ceiling
+    WriteRegister(REG_COM9, 0xca);
+
+    // Disable auto-exposure, enable auto-gain
+    WriteRegister(REG_COM8, 0xec);
+
+    // // Disable auto-gain, enable auto-exposure
+    // WriteRegister(REG_COM8, 0xe9);
+
+    // Use histogram-based auto-exposure
+    WriteRegister(REG_NALG, 0x94);
+
+    // Increase AEC speed:
+    // ‘Decrease TPL but not less than UPL [default 0xc1] and increase TPH but
+    // not bigger than LPH [default 0xf0]’
+    WriteRegister(REG_TPL, 0xc1);
+    WriteRegister(REG_TPH, 0xf0);
+
     // Enable VSYNC interrupts. TIM3 is enabled at the first VSYNC.
     FrameCount = 0;
     Camera_Captured = 0;
@@ -327,20 +348,34 @@ void TIM1_CC_IRQHandler(void)
     CurrentLine = 0;
     FrameCount++;
 
-#ifdef CAMERA_USE_EXPOSURE_CORRECTION
+#ifdef CONFIG_USE_EXPOSURE_CORRECTION
     // Correct exposure across frames
     ExposureCorrection += 32 * BlackPixels / CAMERA_PIXELS - 16;
 #endif
 
     // Check if the last frame's exposure is reasonable
-    if(FrameCount >= 5)
+    if(!Camera_Captured && FrameCount >= CONFIG_MIN_FRAMES
+        && (
+            (BlackPixels > (int)(CAMERA_PIXELS / 2
+                - CAMERA_PIXELS * CONFIG_TOLERANCE)
+            && BlackPixels < (int)(CAMERA_PIXELS / 2
+                + CAMERA_PIXELS * CONFIG_TOLERANCE))
+            || FrameCount >= CONFIG_MAX_FRAMES
+        ))
     {
         Camera_Captured = 1;
+        Camera_FinalFrameCount = FrameCount;
         // Disable everything
         TIM3->CR1 = 0;
         TIM1->CR1 = 0;
     }
 
+    if(FrameCount < (int)(sizeof(Camera_BlackPixelCounts)
+        / sizeof(Camera_BlackPixelCounts[0])))
+    {
+        Camera_BlackPixelCounts[FrameCount] = BlackPixels;
+    }
+
     // Reset black pixel counter
     BlackPixels = 0;
 
@@ -361,7 +396,7 @@ void TIM3_IRQHandler(void)
     DMA1_Channel6->CCR = DMA_CCR_PL | DMA_CCR_MINC | DMA_CCR_EN;
     TIM3->DIER |= TIM_DIER_CC1DE;
 
-#ifdef CAMERA_USE_2D_DITHERING
+#ifdef CONFIG_USE_2D_DITHERING
     static int8_t y_errors[CAMERA_IMAGE_WIDTH + 2] = {0};
 
     if(CurrentLine == 0)
@@ -374,7 +409,7 @@ void TIM3_IRQHandler(void)
         && (CurrentLine / 2 < CAMERA_IMAGE_HEIGHT))
     {
 
-#ifdef CAMERA_USE_2D_DITHERING
+#ifdef CONFIG_USE_2D_DITHERING
         // Apply errors propagated from the previous line. Since y_errors is
         // overwritten during x error diffusion, this is done now.
         for(int i = 0; i < CAMERA_IMAGE_WIDTH; i++)
@@ -388,7 +423,7 @@ void TIM3_IRQHandler(void)
         for(int i = 0; i < CAMERA_IMAGE_WIDTH; i++)
         {
             int pixel = LineBuffer[i + 15] + x_error;
-#ifdef CAMERA_USE_EXPOSURE_CORRECTION
+#ifdef CONFIG_USE_EXPOSURE_CORRECTION
             if(ExposureCorrection < 0)
             {
                 if(pixel < -ExposureCorrection)
@@ -421,7 +456,7 @@ void TIM3_IRQHandler(void)
                     ~(0x80 >> (i % 8));
             }
 
-#ifdef CAMERA_USE_2D_DITHERING
+#ifdef CONFIG_USE_2D_DITHERING
             // Error propagated to the next pixel in the same line
             x_error = error * 7 / 16;
 

src/ov7670.h

@@ -2,19 +2,16 @@
 
 #include <stdlib.h>
 #include "stm32f1xx.h"
+#include "config.h"
 
 #define CAMERA_IMAGE_WIDTH      160
 #define CAMERA_IMAGE_HEIGHT     144
 #define CAMERA_PIXELS           (CAMERA_IMAGE_WIDTH * CAMERA_IMAGE_HEIGHT)
 
-// Use 2D Floyd-Steinberg dithering. Uncomment to use simple line-wise
-// dithering.
-#define CAMERA_USE_2D_DITHERING
-
-// Use a primitive autoexposure by shifting each frames luminosity based on the
-// ratio of white to black pixels in the previous frames
-// #define CAMERA_USE_EXPOSURE_CORRECTION
 
 extern volatile int Camera_Captured;
 
+extern volatile unsigned int Camera_BlackPixelCounts[CONFIG_MAX_FRAMES];
+extern volatile int Camera_FinalFrameCount;
+
 void Camera_Init(void);