Reading an image file in C/C++

Question

I need to read an image file in C/C++. It would be very great, if some one can post the code for me.

I work on gray scale images and the images are JPEG. I would like to read the images into a 2D array which will make my work easy.

Answer 1

If you decide to go for a minimal approach, without libpng/libjpeg dependencies, I suggest using stb_image and stb_image_write, found here.

It's as simple as it gets, you just need to place the header files stb_image.h and stb_image_write.h in your folder.

Here's the code that you need to read images:

#include <stdint.h>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

int main() {
    int width, height, bpp;

    uint8_t* rgb_image = stbi_load("image.png", &width, &height, &bpp, 3);

    stbi_image_free(rgb_image);

    return 0;
}

And here's the code to write an image:

#include <stdint.h>

#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

#define CHANNEL_NUM 3

int main() {
    int width = 800; 
    int height = 800;

    uint8_t* rgb_image;
    rgb_image = malloc(width*height*CHANNEL_NUM);

    // Write your code to populate rgb_image here

    stbi_write_png("image.png", width, height, CHANNEL_NUM, rgb_image, width*CHANNEL_NUM);

    return 0;
}

You can compile without flags or dependencies:

g++ main.cpp

Other lightweight alternatives include:

• lodepng to read and write png files
• jpeg-compressor to read and write jpeg files

Answer 2

You could write your own by looking at the JPEG format.

That said, try a pre-existing library like CImg, or Boost's GIL. Or for strictly JPEG's, libjpeg. There is also the CxImage class on CodeProject.

Here's a big list.

Answer 3

Check out Intel Open CV library ...

Answer 4

Check this thread out: read and write image file.

Also, have a look at this other question at Stackoverflow.

Answer 5

corona is nice. From the tutorial:

corona::Image* image = corona::OpenImage("img.jpg", corona::PF_R8G8B8A8);
if (!image) {
  // error!
}

int width  = image->getWidth();
int height = image->getHeight();
void* pixels = image->getPixels();

// we're guaranteed that the first eight bits of every pixel is red,
// the next eight bits is green, and so on...
typedef unsigned char byte;
byte* p = (byte*)pixels;
for (int i = 0; i < width * height; ++i) {
  byte red   = *p++;
  byte green = *p++;
  byte blue  = *p++;
  byte alpha = *p++;
}

pixels would be a one dimensional array, but you could easily convert a given x and y position to a position in a 1D array. Something like pos = (y * width) + x

Answer 6

Try out the CImg library. The tutorial will help you get familiarized. Once you have a CImg object, the data() function will give you access to the 2D pixel buffer array.

Answer 7

Check out the Magick++ API to ImageMagick.