how to convert 16-bit RGB Frame Buffer to a viewable format?

Question

I'm working with someone else's code on a device which can put an image to /dev/fb/0 and show up on video out or send it over the network to a client application.

I don't have access to the old source for the client app, but I know the following about the data:

• 720x480
• 16-bit
• RGB (I'm no sure if it's 5,5,5 or 5,6,5)
• RAW (no headers whatsoever)
• cat-able to /dev/fb/0
• 675kb

How can I give this a header or convert it to JPEG, BMP, or a RAW type that I could then view in a desktop application?

Ultimately, I want it to be jpeg and viewable in a browser, but anything I can see with my eyes will work for now.

Success

(see the comments below)

ffmpeg \
  -vcodec rawvideo \
  -f rawvideo \
  -pix_fmt rgb565 \
  -s 720x480 \
  -i in-buffer.raw \
  \
  -f image2 \
  -vcodec mjpeg \
  out-buffer.jpg

• github.com/coolaj86/image-examples
• image-examples/scripts/rgbtools-torgb
• image-examples/scripts/rgbtools-fromrgb

Failed Attempts

Shows the image three times widthwise with almost no color, and squashed vertically:

rawtoppm -rgb -interpixel 720 480 fb.raw > fb.ppm

Shows the image, but with streaks and squashed vertically and bad color:

rawtoppm -rgb -interrow 720 480 fb.raw > fb.ppm

Similar to the above

convert -depth 16 -size 720x480 frame_buffer.rgb fb.jpeg

Solution 1

rgb to ppm: Just season to taste!

maintained at https://github.com/coolaj86/image-examples

#include <stdio.h>

int main(int argc, char* argv[]) {

  FILE* infile; // fb.raw
  FILE* outfile; // fb.ppm
  unsigned char red, green, blue; // 8-bits each
  unsigned short pixel; // 16-bits per pixel
  unsigned int maxval; // max color val
  unsigned short width, height;
  size_t i;

  infile = fopen("./fb.raw", "r");
  outfile = fopen("./fb.ppm", "wb");
  width = 720;
  height = 480;
  maxval = 255;

  // P3 - PPM "plain" header
  fprintf(outfile, "P3\n#created with rgb2ppm\n%d %d\n%d\n", width, height, maxval);

  for (i = 0; i < width * height; i += 1) {
      fread(&pixel, sizeof(unsigned short), 1, infile);

      red = (unsigned short)((pixel & 0xF800) >> 11);  // 5
      green = (unsigned short)((pixel & 0x07E0) >> 5); // 6
      blue = (unsigned short)(pixel & 0x001F);         // 5

      // Increase intensity
      red = red << 3;
      green = green << 2;
      blue = blue << 3;

    // P6 binary
    //fwrite(&(red | green | blue), 1, sizeof(unsigned short), outfile);

    // P3 "plain"
    fprintf(outfile, "%d %d %d\n", red, green, blue);
  }
}

Solution 2

I'm developing an embedded system with a 5:6:5 RGB format, and on occasion I've needed to capture raw framebuffer data and convert it to a viewable image. For experimentation, I wrote a bit of C code to convert the raw binary values to link text. The format is dumb, but easily readable - thus I found it convenient for hacking about. I then used Imagemagick display to view and convert to convert to JPG. (If I recall correctly, convert will accept raw binary images - but that assumes you know all the image parameters, i.e. 5:6:5 versus 5:5:5).

I can post sample C code to convert 5:6:5 to 8:8:8 RGB if needed.

Comments

[coolaj86]

That would be appreciated. I'm googling about convert right now.

[Throwback1986]

for (size_t i=0;i<num_pixels;i++) { fread(&pixel, sizeof(unsigned short), 1, infile); red = (unsigned short)((pixel & 0xF800) >> 11); green = (unsigned short)((pixel & 0x07E0) >> 5); blue = (unsigned short)(pixel & 0x001F); // Increase intensity red = red << 3; green = green << 2; blue = blue << 3; fprintf(outfile, "%d %d %d\n", red, green, blue); }

[Throwback1986]

Bummer - I forgot that comments cannot be formatted. The above code assumes a 565 pixel. This snippet reads a pixel from a binary file, separates the pixel values into RGB components, scales them appropriately, then writes them out as text.

[coolaj86]

Do you know how I specify rgb as 5:6:5 with convert?