How to convert a raw RGB frame buffer file to a viewable format?

Question

I know this question has been asked previously. Original thread is here how to convert 16-bit RGB Frame Buffer to a viewable format? But i am not getting my desire output.

Well currently I am dealing with frame buffer. The exact picture is that i am accessing frame buffer(/dev/graphics/fb0) of an android phone (through "adb" shell). I used "dd" to get the frame buffer.

cd /dev/graphics

dd if=fb0 of=/sdcard/fb0.raw bs=1 count=width*height*3 //this width and height are based on mobile screen specification. And 3 is for RGB888

I used this code -

#include <stdio.h>
#include <stdlib.h>
#include <bmpfile.h>

int main(int argc, char **argv)
{
bmpfile_t *bmp;
int i, j;
char* infilename;
FILE* infile;
char* outfile;
int width;
int height;
int depth;
unsigned char red, green, blue; // 8-bits each
unsigned short pixel; // 16-bits per pixel
//rgb_pixel_t bpixel = {128, 64, 0, 0};
//make && ./raw565tobmp fb.rgb565 720 480 32 fb.bmp && gnome-open fb.bmp

if (argc < 6) {
printf("Usage: %s infile width height depth outfile.\n", argv[0]);
exit(EXIT_FAILURE);
}

infilename = argv[1];
outfile = argv[5];

infile = fopen(infilename, "rb");
if (NULL == infile) {
perror("Couldn't read infile");
exit(EXIT_FAILURE);
}

width = atoi(argv[2]);
height = atoi(argv[3]);
depth = atoi(argv[4]);

// should be depth/8 at 16-bit depth, but 32-bit depth works better
short buffer[height*width*(depth/16)];
printf("depth: %d", depth);
if (fread(&buffer, 1, height*width*(depth/16), infile) != height*width*(depth/16)) {
 fputs("infile dimensions don't match the size you supplied\n", stderr);
}
printf("depth: %d", depth);

if ((bmp = bmp_create(width, height, depth)) == NULL) {
printf("Invalid depth value: '%d'. Try 1, 4, 8, 16, 24, or 32.\n", depth);
exit(EXIT_FAILURE);
}

for (i = 0; i < width; ++i) { // 720
 for (j = 0; j < height; ++j ) { // 480
  pixel = buffer[width*j+i];

  red = (unsigned short)((pixel & 0xFF0000) >> 16);  // 8
  green = (unsigned short)((pixel & 0x00FF00) >> 8); // 8
  blue = (unsigned short)(pixel & 0x0000FF);         // 8

  rgb_pixel_t bpixel = {blue, green, red, 0};
  bmp_set_pixel(bmp, i, j, bpixel);
  }
}

bmp_save(bmp, outfile);
bmp_destroy(bmp);

return 0;
}

Input of this program - ./a.out fb0.raw 480 854 24 /data/new.bmp

argv[1]=input file

argv[2]=width

argv[3]=height

argv[4]=depth

argv[5]=output file

originally the code is given here how to convert 16-bit RGB Frame Buffer to a viewable format?

Now here after opening the bmp file i am getting every thing is BLACK. Why this is so?

And how to display the frame buffer?

score 2 · Answer 1 · answered Jun 05 '13 at 09:40

To not re-invent the wheel, I tried to re-use existing tool:

Get the framebuffer:
```
adb pull /dev/graphics/fb0 androidFB
```

Find what is the format used in our framebuffer file. I use the utility avconv for that purpose (but you can also use ffmpeg), associated with a homemade script:

#!/bin/bash

#Change FB_RESOLUTION value by the android device's resolution
FB_RESOLUTION=240x320
OUTPUT_DIR=fbresult

#format come from: avconv -pix_fmts| cut -f 2 -d " "
format=(yuv420p yuyv422 rgb24 bgr24 yuv422p yuv444p yuv410p yuv411p gray monow monob pal8 yuvj420p yuvj422p yuvj444p xvmcmc xvmcidct uyvy422 uyyvyy411 bgr8 bgr4 bgr4_byte rgb8 rgb4 rgb4_byte nv12 nv21 argb rgba abgr bgra gray16be gray16le yuv440p yuvj440p yuva420p vdpau_h264 vdpau_mpeg1 vdpau_mpeg2 vdpau_wmv3 vdpau_vc1 rgb48be rgb48le rgb565be rgb565le rgb555be rgb555le bgr565be bgr565le bgr555be bgr555le vaapi_moco vaapi_idct vaapi_vld yuv420p16le yuv420p16be yuv422p16le yuv422p16be yuv444p16le yuv444p16be vdpau_mpeg4 dxva2_vld rgb444le rgb444be bgr444le bgr444be y400a bgr48be bgr48le yuv420p9be yuv420p9le yuv420p10be yuv420p10le yuv422p10be yuv422p10le yuv444p9be yuv444p9le yuv444p10be yuv444p10le yuv422p9be yuv422p9le vda_vld gbrp gbrp9be gbrp9le gbrp10be gbrp10le gbrp16be gbrp16le)


mkdir $OUTPUT_DIR

for item in ${format[*]}
do
    #Loop through operation   
    avconv -vframes 1 -f rawvideo -pix_fmt $item -s $FB_RESOLUTION -i androidFB $OUTPUT_DIR/$item.png
done

Browse OUTPUT_DIR directory to find image that have the right appearance. The name of the file is the format to use : XXXX.png the format to use will be XXXX
You can now convert the framebuffer in PNG with the command below (don't forget to replace resolution FB_RESOLUTION and format XXXX by correct value)
```
avconv -vframes 1 -f rawvideo -pix_fmt XXXX -s FB_RESOLUTION -i androidFB androidFB.png
```

score 2 · Answer 2 · answered Sep 02 '14 at 03:59

I have been trying to capture an Android 2.3.4 mobile screen image and had the same problems. First I was trying with some tools, but I was complicating everything.

Joe gave me the clue about the padding, so I just try reading the raw framebuffer in a file, to load it with GIMP (in this moment I am not interested on making software for that, maybe later).

And playing with the GIMP raw import parameters I found that with the padding the width for a 240x320 screen is really 256x320 with transparent padding on the right. Also it was not an RGB but an "RGB Alpha" raw type.

As what I am working on is a manual, the following, together with GIMP was enough to work this on the old Android version:

adb shell "cat /dev/graphics/fb0 > /mnt/sdcard/documents/devimages/$1.data"
adb pull /mnt/sdcard/documents/devimages/$1.data
adb shell "rm /mnt/sdcard/documents/devimages/$1.data"

I hope this helps somebody :-)

score 1 · Answer 3 · answered Sep 17 '12 at 13:19

well to gain a lot of convencience and functionality, you could use an OpenCV Port for android. then it would be one of the most simple things. I dont think it would be much of a problem since you are using natice code in your project.

If i remember correctly, the function is named imwrite() and located in HighGui.hpp

You can find an android port of the OpenCV here: http://opencv.org/downloads.html

Related "blackness" problem: I faced this issue when working with pgm images. PGM headers must specify a "maximum" depth for the image. E.G. 255, 8bit. Imagine you have 8 bit data, but working with a MAXIMUM resolution of 16 bit, 65565 values. the picture would be "black" because all the values are so low. I hope you know what i mean.

The above input is not the only one i tried. I tried with different values of depth, width and height but unfortunately end result was BLACK screen. — user1659320, Sep 18 '12 at 05:05

Joe Plante · Answer 4 · 2012-09-17T13:14:38.207

  rgb_pixel_t bpixel = {blue, green, red, 0};

Might be setting the alpha value to 0, and alpha is a transparency value. Try 255 instead to see if you get any results at all. If you have the pixel equations wrong, you should at least get something.

Another "gotcha" with images is that sometimes the data isn't stored as RGBRGBRGB... but BGRBGRBGR like in the Microsoft/IBM DIB. It's an easy check because you'll get the image, but it would be like you are on LSD.

height*width*(depth/16)

Should also be looked at. I would also recommend putting this into a variable once so that it's easier for you to maintain.

Also, one thing to watch out about RAW DIBs: sometimes they have a set padding per line. In the MS/IBM DIB, it's a requirement that each scanline has to be stored in 4 byte increments. So, if your output shifts to one direction a lot, it could be that. In some cases, the image is stored upside-down

I tried with 255 instead of 0 but didn't work. What i am getting is BLACK. — user1659320, Sep 18 '12 at 04:43

How to convert a raw RGB frame buffer file to a viewable format?

4 Answers4