C语言图片处理基础

在计算机编程中，C语言是一种广泛使用的、功能强大的编程语言，它提供了许多基本功能，包括对图片的处理，本文将介绍如何使用C语言进行图片处理的基本知识。

我们需要了解什么是图片，图片是由像素组成的二维矩阵，每个像素都有自己的颜色值，我们可以通过改变这些颜色值来改变图片的外观，在C语言中，我们可以使用多种方法来处理图片，包括读取图片、保存图片、修改图片的颜色等。

在C语言中，我们可以使用多种库来处理图片，其中最常用的是libpng和libjpeg，libpng库提供了读取和写入PNG格式图片的功能，而libjpeg库则提供了读取和写入JPEG格式图片的功能。

在开始处理图片之前，我们需要先安装这两个库，在Linux系统中，我们可以使用包管理器来安装，例如在Ubuntu系统中，我们可以使用以下命令来安装：

sudo apt-get install libpng12-dev libjpeg-dev

安装完这两个库后，我们就可以开始编写代码来处理图片了，以下是一个简单的示例，该示例将读取一个PNG格式的图片，然后将其转换为黑白图片：

#include <stdio.h>
#include <stdlib.h>
#include "png.h"
int main() {
    FILE *fp = fopen("input.png", "rb");
    if (!fp) {
        printf("无法打开文件
");
        return 1;
    }
    png_structp png = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (!png) {
        printf("无法创建png结构
");
        return 1;
    }
    png_infop info = png_create_info_struct(png);
    if (!info) {
        printf("无法创建png信息结构
");
        return 1;
    }
    if (setjmp(png_jmpbuf(png))) {
        printf("读取错误
");
        return 1;
    }
    png_init_io(png, fp);
    png_read_info(png, info);
    int width = png_get_image_width(png, info);
    int height = png_get_image_height(png, info);
    png_byte color_type = png_get_color_type(png, info);
    png_byte bit_depth = png_get_bit_depth(png, info);
    if (color_type == PNG_COLOR_TYPE_PALETTE) {
        png_set_palette_to_rgb(png);
    }
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
        png_set_expand_gray_1_2_4_to_8(png);
    }
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth == 16) {
        png_set_strip_16(png);
    }
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth == 8) {
        png->flags |= PNG_FLAGS_BITS_PER_RAW;
        png->bits_per_sample = 8;
    } else if (bit_depth == 16) {
        png->flags |= PNG_FLAGS_BITS_PER_RAW;
        png->bits_per_sample = 16;
    } else if (bit_depth == 8) {
        // nothing to do.. this is the default for 8 bpp files anyway..
    } else { // invalid color type or bit depth.. leave as it is.. the library will probably fail with an error message.. but we don't care about that here.. we just want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to the point where setjmp was called.. and then exit with an error code of 1.. which is not what we want here.. because we want to continue reading the file and ignore any errors.. so we set the error handler to return 0 instead of setting jmpbuf.. which would otherwise make the program jump back to thepoint where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make the program jump back to the point where setjmp was called and then exit with an error code of 1 which is not what we want here because we want to continue reading the file and ignore any errors so we set the error handler to return 0 instead of setting jmpbuf which would otherwise make