CImg：如何保存灰度？

发布于 2024-11-06 05:18:32 字数 339 浏览 1 评论 0原文

当我使用CImg加载.BMP时，我如何知道它是灰度图像还是彩色图像？我尝试了如下，但失败了：

cimg_library::CImg<unsigned char> img("lena_gray.bmp");

const int spectrum = img.spectrum();

img.save("lenaNew.bmp");

按照我的预期，无论我加载哪种.BMP，频谱总是3。因此，当我加载灰度并保存时它，结果大小将比实际大 3 倍。

我只想保存加载时相同的图像。如何保存为灰度？

原文

When I use CImg to load a .BMP, how can I know whether it is a gray-scale or color image?
I have tried as follows, but failed:

cimg_library::CImg<unsigned char> img("lena_gray.bmp");

const int spectrum = img.spectrum();

img.save("lenaNew.bmp");

To my expectation, no matter what kind of .BMP I have loaded, spectrum will always be 3. As a result, when I load a gray-scale and save it, the result size will be 3 times bigger than it is.

I just want to save a same image as it is loaded. How do I save as gray-scale?

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洛阳烟雨空心柳 2024-11-13 05:18:32

我猜想 BMP 格式总是将图像存储为 RGB 编码数据，因此读取 BMP 总是会生成彩色图像。
如果您知道您的图像是标量，则所有通道都将相同，因此您可以丢弃其中两个（此处保留第一个）。

img.channel(0);

如果您想检查它是否是标量图像，您可以测试通道之间的相等性，如下所示

const CImg<unsigned char> R = img.get_shared_channel(0),
                          G = img.get_shared_channel(1),
                          B = img.get_shared_channel(2);
if (R==G && R==B) {
    .. Your image is scalar !
} else {
    .. Your image is in color.
}

I guess the BMP format always store images as RGB-coded data, so reading a BMP will always result in a color image.
If you know your image is scalar, all channels will be the same, so you can discard two of them (here keeping the first one).

img.channel(0);

If you want to check that it is a scalar image, you can test the equality between channels, as

const CImg<unsigned char> R = img.get_shared_channel(0),
                          G = img.get_shared_channel(1),
                          B = img.get_shared_channel(2);
if (R==G && R==B) {
    .. Your image is scalar !
} else {
    .. Your image is in color.
}

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