Thread: reading image

  1. #1
    Registered User
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    Feb 2017

    reading image

    how can i read jpg format images (or) pixel values

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    First of all, let's assume that you're not using TurboC as your compiler.

    That being the case, the easiest way to read a JPG file into a format where you can read pixels is to use a library.
    libjpeg - Wikipedia

    Yes, you can use fopen() to open the file, and fread() to read the whole file into memory.
    But extracting pixels from the binary data involves a LOT of work, and a LOT of very serious maths.
    If you want reasonable results in anything less than 6 months, then use a library.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
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    May 2012
    Here's code for loading JPEGs and all the other popular file formats for good measure.

    GitHub - MalcolmMcLean/babyxrc: Resource compiler, packages images, fonts, cursors, etc as compilable C source. Portable ANSI C.
    I'm the author of MiniBasic: How to write a script interpreter and Basic Algorithms
    Visit my website for lots of associated C programming resources.

  4. #4
    Registered User
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    Feb 2017
    stb_image makes reading images quite painless. It's just a single header file you include in your own code, and that's it. Also it's a public domain license.

    Here's a dumb example of reading the first 10 pixels of a JPG file...

    #include <stdio.h>
    #include "stb_image.h"
    const size_t NUM_PIXELS_TO_PRINT = 10U;
    int main(void) {
        int width, height, comp;
        unsigned char *data = stbi_load("image.jpg", &width, &height, &comp, 0);
        if (data) {
            printf("width = %d, height = %d, comp = %d (channels)\n", width, height, comp);
            for (size_t i = 0; i < NUM_PIXELS_TO_PRINT * comp; i++) {
                printf("%02x%s", data[i], ((i + 1) % comp) ? "" : "\n");
        return 0;

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