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Forum: µC & Digital Electronics Convert YUV(4:2:2) format to BMP file by use of OV9655 image sensor


Author: Jan Heiby (janheiby)
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Hello anyone
I working on OV9655 camera module that is connected to stm32f4discover 
evaluation board. I am able to capture a picture from the OV9655 module 
where the video output format is based on RGB565 and save as BMP file on 
SD cart.  Now I want to capture a gray scale picture and save it as BMP 
file. For that purpose do use YUV(4:2:2:) video format
The picture size is 120*160.
As I am is aware does YUV(4:2:2) format consist of 4 byte: Yo,Uo,Y1,Vo 
that sent out through OV9655 video interface. The OV9655 interface is 
connected to DCIM interface on STM32F407 microcontroller.
The following register setting is use to up OV9655 image chip to send 
out YUV(4:2:2) video format.
 OV9655 COM7 Register setting:
    Bit7=0  no changed
                                       Bit6..4 = 110 30fps VGA with 
VerioPixel.
                                       Bit 3..2 not used
                                       Bit 1..0 10 YUV RGB data
The OV9655 TSL Register setting:
    Bit 7..6  11  PCL output delay set to 6 ns
                                       Bit5       0
                                       Bit4      0  Normal UV output
    Bit3.2   00  YUYV  output sequence
                                       Bit 1     0
                                       Bit 0     not used
OV9655 COM15 Register:
                     Bit 7..6  10 Output range [01] to [FE]
                                      Bit 5..4  Normal RGB output
                                      Bit 3..0  Not Used.
But I am not sure about that above setting for OV9655 is correct.
After the picture is grab by used of DCIM on STM32F407 microcontroller 
do I want to convert it to BMP file. Right now do I use the same code 
that is use during conversation of RGB565 to transform YUV(4:2:2) format 
to BMP file. The code work fine during conversation of RGB565 to BMP 
file.
But is it possible to use the same procedure during the conversation of 
YUV(4:2:2) format to BMP file?
Can the same BMP header that is use for RGB565 be use on the YUV(4:2:2) 
video format

// BMP Header
#ifdef QQVGA
//@brief  Set the QQVGA size(120*160).
uint8_t bmp_header[70] = {
  0x42, 0x4D, // ID field // BM
  0x46, 0x58, 0x02, 0x00, // Size of BMP file 153670 bytes
  0x00, 0x00, 0x00, 0x00, // Not use Application specific
  0x46, 0x00, 0x00, 0x00, // Offset where the pixel array can be found 
70
  // DIB Header
  0x28, 0x00, 0x00, 0x00, // Number of bytes in the DIB header (from 
this point) 40 bytes
  0xA0, 0x00, 0x00, 0x00, // Width of the bitmap in pixel 160
  0x78, 0x00, 0x00, 0x00, // Height of the bitmap in  pixel 120
  0x01,  0x00,             // Plane
  0x10,  0x00,             // 16 bits number of bits pr pixels
  0x03, 0x00, 0x00, 0x00, // BI_RGB
  0x00, 0x58, 0x02, 0x00, // pixels/meter horizontal
  0x00, 0x00, 0x00, 0x00, // pixels/meter vertical
  0x00, 0x00, 0x00, 0x00, // Number ofcolors in the palette
  0x00, 0x00, 0x00, 0x00, // 0 means all color are important
  // Start of pixel array
  0x00, 0x00, 0x00,       // Red, Pixel(0,1)
  0x00,  0x00, 0xF8,        // write, Pixel(1,1)
  0x00, 0x00,              // Pading for 4 byte alligment
  0xE0, 0x07, 0x00,       // Blue, Pixel
  0x00, 0x1F, 0x00,       // Green Pixel
  0x00, 0x00,              // Padding for 4 byte
  0x00, 0x00, 0x00, 0x00
};
#endif



/* write the bmp header */
ret = f_write(&file, bmp_header, 70,(UINT*)&bw);
The code loop that handle the BMP conversation is as follow.
// QQVGA size(120*160).
for (j = 0; j < 120; j++)
{
  for(i=0;i<160;i++)
  {
      data_temp = frameptr[counter];
      // MSB Byte of 16 bit
      image_buf[i*2+1] = (data_temp&0xff00) >> 8;
      // LSB Byte of 16 bit
      image_buf[i*2+0] = data_temp & 0x00ff;
      counter++;
  }
   ret = f_write(&file, image_buf, 320,(UINT*)&bw);
}

ret = f_close(&file);

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