从RGB BMP创建灰度BMP [英] Create greyscale BMP from RGB BMP

问题描述

我有24位图像，我读了位图，并将其转换为灰度并保存像8位。

I have 24-bit image, I read bitmap and transform it to the grayscale and save like 8-bit.

RGBTRIPLE temp;
unsigned char t;
...
t = (temp.rgbtBlue * 0.114 + temp.rgbtGreen * 0.587 + temp.rgbtRed * 0.299);
fwrite(&t, sizeof(UCHAR), 1, newFile);

在该图像没开，我明白我必须在水木清华头改变。
我试着文件，并在头位的大小，改变大小，但它并没有正常工作。

After that image didn't open, I understand I must smth to change in headers. I try change size of file and size of bitmap in headers, but it didn't working.

BITMAPFILEHEADER bfh;
BITMAPINFOHEADER bih;
...
bfh.bfSize = sizeof(UCHAR) * img.Width * img.Height + bfh.bfOffBits;
bih.biSizeImage = sizeof(UCHAR) * img.Width * img.Height;
bih.biCompression = BI_BITFIELDS;
bih.biBitCount = 8;

我需要像8位BMP更改保存图像？

What I need to change for save image like 8-bit BMP?

推荐答案

其实，最简单的方法是不改变在任何头。你读3个值（RGB），将它们转换使用标准的PAL / NTSC公式为灰色，然后你就可以输出所计算出的灰度值的3倍了。这样一来，你又得到1个像素，但改变的值。

Actually, the easiest way is not to change anything in the headers. You read 3 values (RGB), convert them to gray using the standard PAL/NTSC formula, and then you can output the calculated gray value 3 times back. That way, you get 1 pixel again, but with the altered value.

您只需更改只是头不为8位，因为工作，的颜色索引的形象，您还需要提供一个颜色索引地图 - 中的调色板。此外，根据原始图像的大小，你可能需要更改每行的步幅的（这就是它被称为 - 谷歌是你的朋友太）。

Your simply changing just the header doesn't work because for an 8-bit, color indexed image, you also need to provide a color index map -- the palette. In addition, depending on the original image size, you may need to change the stride of each row (that's what it is called -- Google is your friend too!).

正如马克·瑟特查的言论，BI_BITFIELDS是不是你在这里需要什么（维基百科上BMP ）。使用BI_RGB一个真正的颜色或颜色索引图像;其他值的非常的专业 - 我从来没有见过他们在野外

As Mark Setchell remarks, BI_BITFIELDS is not what you need here (Wikipedia on BMP). Use BI_RGB for a true color or color indexed image; the other values are very specialized -- and I've never seen them "in the wild".

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