Fundamentals of Image Processing in C: Reading and Displaying Images

In modern programming, image processing is an important field. Although C is not specifically designed for image processing, it provides powerful low-level operation capabilities that allow us to implement basic image reading and displaying functions. In this article, we will introduce how to perform simple image processing using C, including how to read and display an image.

1. Preparation

Before we begin, please ensure that you have installed the following tools:

• C compiler (such as GCC)
• Graphics library (such as SDL or OpenCV)

To simplify the example, we will use the SDL library for loading and displaying images. Please install the appropriate version of SDL for your operating system.

Installing SDL

For Ubuntu users, you can install SDL with the following command:

sudo apt-get install libsdl2-dev

For Windows users, you can download the development package from the SDL official website and configure it in your IDE.

2. Basic Concepts

In computers, images are typically stored in bitmap (Bitmap) format. Each point (or pixel) has its corresponding color value. In our example, we will use the PNG format as the input file because it is a common and lossless compression format.

3. Code Example for Reading and Displaying Images

Below is a simple example demonstrating how to load and display a PNG image using C and the SDL library.

Example Code

#include <stdio.h>
#include <stdlib.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>

int main(int argc, char* argv[]) {
    // Initialize SDL
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        fprintf(stderr, "Unable to initialize SDL: %s\n", SDL_GetError());
        return EXIT_FAILURE;
    }

    // Create window
    SDL_Window* window = SDL_CreateWindow("Image Display",
                                          SDL_WINDOWPOS_CENTERED,
                                          SDL_WINDOWPOS_CENTERED,
                                          800, 600,
                                          0);
    if (!window) {
        fprintf(stderr, "Unable to create window: %s\n", SDL_GetError());
        SDL_Quit();
        return EXIT_FAILURE;
    }

    // Create renderer
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, 0);
    if (!renderer) {
        fprintf(stderr, "Unable to create renderer: %s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return EXIT_FAILURE;
    }

    // Load image
    const char* imagePath = "path/to/your/image.png"; // Replace with your image path
    IMG_Init(IMG_INIT_PNG); // Initialize PNG support

    // Load texture
    SDL_Texture* texture = IMG_LoadTexture(renderer, imagePath);
    if (!texture) {
        fprintf(stderr, "Unable to load texture: %s\n", IMG_GetError());
        SDL_DestroyRenderer(renderer);
        SDL_DestroyWindow(window);
        IMG_Quit();
        SDL_Quit();
        return EXIT_FAILURE;
    }

    // Main loop flag variable
    int running = 1;
    SDL_Event event;
    while (running) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                running = 0;
            }
        }

        // Clear screen and set background color
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
        SDL_RenderClear(renderer);

        // Render texture
        SDL_RenderCopy(renderer, texture, NULL, NULL);

        // Present rendered result
        SDL_RenderPresent(renderer);
    }

    // Clean up resources
    SDL_DestroyTexture(texture);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    IMG_Quit();
    SDL_Quit();

    return EXIT_SUCCESS;
}

Program Explanation

1. Initialization: First, we need to initialize the <span>SDL</span> library. If initialization fails, an error message will be output and the program will exit.
2. Create Window: Next, we create a window to display our image.
3. Create Renderer: The renderer is used to draw content onto the window.
4. Load Image: We use the <span>IMG_LoadTexture</span> function to load a PNG image from the specified path. If loading fails, an error message will also be output.
5. Main Loop:

• We enter a loop that continuously checks for events, such as the window close event.
• In each iteration of the loop, we clear the screen, set the background color, then draw the texture on the screen and update the display content.

Clean Up Resources: When the program ends, we need to free all allocated resources to avoid memory leaks.

Conclusion

This article introduced how to use C in conjunction with the SDL library for basic image reading and displaying. Through this simple example, you should be able to understand the basic process and try to expand more functionalities, such as adding buttons, responding to keyboard events, etc. This is just a beginner-level introduction, and I hope it inspires your interest in exploring more complex projects!