如何通过cimg获取rgb值？

发布于 2024-09-10 19:09:28 字数 209 浏览 2 评论 0原文

CImg<unsigned char> src("image.jpg");
int width = src.width();
int height = src.height();
unsigned char* ptr = src.data(10,10);

如何从 ptr 获取 rgb？

原文

CImg<unsigned char> src("image.jpg");
int width = src.width();
int height = src.height();
unsigned char* ptr = src.data(10,10);

How can I get rgb from ptr?

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久光 2024-09-17 19:09:28

在 Ubuntu 10.04 上测试，使用手工制作的 3x3 RGB 图像保存为 test.png：

sudo apt-get install cimg-dev

源文件 cimg_test.cpp：

#include <iostream>
using namespace std;

#include <CImg.h>
using namespace cimg_library;

int main()
{
    CImg<unsigned char> src("test.png");
    int width = src.width();
    int height = src.height();
    cout << width << "x" << height << endl;
    for (int r = 0; r < height; r++)
        for (int c = 0; c < width; c++)
            cout << "(" << r << "," << c << ") ="
                 << " R" << (int)src(c,r,0,0)
                 << " G" << (int)src(c,r,0,1)
                 << " B" << (int)src(c,r,0,2) << endl;
    return 0;
}

编译并运行：

g++ cimg_test.cpp -lX11 -lpthread -o cimg_test

./cimg_test 
3x3
(0,0) = R0 G0 B0
(0,1) = R255 G0 B0
(0,2) = R0 G255 B0
(1,0) = R0 G0 B255
(1,1) = R128 G128 B128
(1,2) = R0 G0 B128
(2,0) = R128 G0 B0
(2,1) = R0 G128 B0
(2,2) = R255 G255 B255

它可以工作。

Tested on Ubuntu 10.04 with a handmade 3x3 RGB image saved as test.png:

sudo apt-get install cimg-dev

Source file cimg_test.cpp:

#include <iostream>
using namespace std;

#include <CImg.h>
using namespace cimg_library;

int main()
{
    CImg<unsigned char> src("test.png");
    int width = src.width();
    int height = src.height();
    cout << width << "x" << height << endl;
    for (int r = 0; r < height; r++)
        for (int c = 0; c < width; c++)
            cout << "(" << r << "," << c << ") ="
                 << " R" << (int)src(c,r,0,0)
                 << " G" << (int)src(c,r,0,1)
                 << " B" << (int)src(c,r,0,2) << endl;
    return 0;
}

Compile and run:

g++ cimg_test.cpp -lX11 -lpthread -o cimg_test

./cimg_test 
3x3
(0,0) = R0 G0 B0
(0,1) = R255 G0 B0
(0,2) = R0 G255 B0
(1,0) = R0 G0 B255
(1,1) = R128 G128 B128
(1,2) = R0 G0 B128
(2,0) = R128 G0 B0
(2,1) = R0 G128 B0
(2,2) = R255 G255 B255

It works.

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红尘作伴 2024-09-17 19:09:28

来自CImg 文档 - 第 34 页第 6.13 节和第 120 页第 8.1.4.16 节-- 看起来 data 方法可以采用四个参数：x、y、z 和 c:

T* data(const unsigned int x, const unsigned int y = 0, 
        const unsigned int z = 0, const unsigned int c = 0)

...其中 c 指的是颜色通道。我猜测，如果您的图像确实是 RGB 图像，那么对 c 使用 0、1 或 2 的值将为您提供给定 处的红色、绿色和蓝色分量x, y 位置。

例如：（

unsigned char *r = src.data(10, 10, 0, 0);
unsigned char *g = src.data(10, 10, 0, 1);
unsigned char *b = src.data(10, 10, 0, 2);

但这只是一个猜测！）

编辑：

CImg 似乎还有一个以类似方式工作的operator()：

unsigned char r = src(10, 10, 0, 0);

From the CImg documentation -- section 6.13 on page 34, and section 8.1.4.16 on page 120 -- it looks like the data method can take four arguments: x, y, z, and c:

T* data(const unsigned int x, const unsigned int y = 0, 
        const unsigned int z = 0, const unsigned int c = 0)

...where c refers to the color channel. I'm guessing that if your image is indeed an RGB image, then using values of 0, 1, or 2 for c will give you the red, green, and blue components at a given x, y location.

For example:

unsigned char *r = src.data(10, 10, 0, 0);
unsigned char *g = src.data(10, 10, 0, 1);
unsigned char *b = src.data(10, 10, 0, 2);

(But this is just a guess!)

Edit:

It looks like there's also an operator() for CImg that works in a similar manner:

unsigned char r = src(10, 10, 0, 0);

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谎言月老 2024-09-17 19:09:28

访问数据的最简单方法是使用 () 运算符：

unsigned char r = img(10,10,0,0);
unsigned char g = img(10,10,0,1);
unsigned char b = img(10,10,0,2);

您可能会感到困惑，因为 CImg 以非交错方式存储原始数据。即您的原始数据存储为 R1, R2, ..., G1, G2, ..., B1, B2, ... 而不是 R1, G1, B1, R2, G2 ，B2，...参见：http://cimg.eu/reference/group__cimg__storage.html

.data() 仅返回一个指针，因此要像上面那样直接访问数据，您可以执行以下操作：

CImg<unsigned char> src("image.jpg");
int width = src.width();
int height = src.height();
unsigned char* ptr = src.data(10,10);
unsigned char r = ptr[0];
unsigned char g = ptr[0+width*height];
unsigned char b = ptr[0+2*width*height];

The easiest way to access data is with the () operator:

unsigned char r = img(10,10,0,0);
unsigned char g = img(10,10,0,1);
unsigned char b = img(10,10,0,2);

You are probably hitting confusion because CImg stores the raw data non-interleaved. i.e. your raw data is stored R1, R2, ..., G1, G2, ..., B1, B2, ... instead of R1, G1, B1, R2, G2, B2, ... see: http://cimg.eu/reference/group__cimg__storage.html

.data() just returns a pointer, so to access the data directly as above you would do:

CImg<unsigned char> src("image.jpg");
int width = src.width();
int height = src.height();
unsigned char* ptr = src.data(10,10);
unsigned char r = ptr[0];
unsigned char g = ptr[0+width*height];
unsigned char b = ptr[0+2*width*height];

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