C# 如何计算位图的平均 rgb 颜色值
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原文地址: http://stackoverflow.com/questions/1068373/
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How to calculate the average rgb color values of a bitmap
提问by Mats
In my C# (3.5) application I need to get the average color values for the red, green and blue channels of a bitmap. Preferably without using an external library. Can this be done? If so, how? Thanks in advance.
在我的 C# (3.5) 应用程序中，我需要获取位图的红色、绿色和蓝色通道的平均颜色值。最好不使用外部库。这能做到吗？如果是这样，如何？提前致谢。
Trying to make things a little more precise: Each pixel in the bitmap has a certain RGB color value. I'd like to get the average RGB values for all pixels in the image.
试图让事情更精确一点：位图中的每个像素都有一个特定的 RGB 颜色值。我想获得图像中所有像素的平均 RGB 值。
采纳答案by Philippe Leybaert
The fastest way is by using unsafe code:
最快的方法是使用不安全的代码：
BitmapData srcData = bm.LockBits(
new Rectangle(0, 0, bm.Width, bm.Height),
ImageLockMode.ReadOnly,
PixelFormat.Format32bppArgb);
int stride = srcData.Stride;
IntPtr Scan0 = srcData.Scan0;
long[] totals = new long[] {0,0,0};
int width = bm.Width;
int height = bm.Height;
unsafe
{
byte* p = (byte*) (void*) Scan0;
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
for (int color = 0; color < 3; color++)
{
int idx = (y*stride) + x*4 + color;
totals[color] += p[idx];
}
}
}
}
int avgB = totals[0] / (width*height);
int avgG = totals[1] / (width*height);
int avgR = totals[2] / (width*height);
Beware: I didn't test this code... (I may have cut some corners)
当心：我没有测试这段代码......（我可能已经偷工减料了）
This code also asssumes a 32 bit image. For 24-bit images. Change the x*4to x*3
此代码还假定为 32 位图像。对于 24 位图像。将x*4更改为x*3
回答by Loofer
This kind of thing will work but it may not be fast enough to be that useful.
这种事情会起作用，但它可能不够快而没有那么有用。
public static Color GetDominantColor(Bitmap bmp)
{
//Used for tally
int r = 0;
int g = 0;
int b = 0;
int total = 0;
for (int x = 0; x < bmp.Width; x++)
{
for (int y = 0; y < bmp.Height; y++)
{
Color clr = bmp.GetPixel(x, y);
r += clr.R;
g += clr.G;
b += clr.B;
total++;
}
}
//Calculate average
r /= total;
g /= total;
b /= total;
return Color.FromArgb(r, g, b);
}
回答by MusiGenesis
Here's a much simpler way:
这是一个更简单的方法：
Bitmap bmp = new Bitmap(1, 1);
Bitmap orig = (Bitmap)Bitmap.FromFile("path");
using (Graphics g = Graphics.FromImage(bmp))
{
// updated: the Interpolation mode needs to be set to
// HighQualityBilinear or HighQualityBicubic or this method
// doesn't work at all. With either setting, the results are
// slightly different from the averaging method.
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.DrawImage(orig, new Rectangle(0, 0, 1, 1));
}
Color pixel = bmp.GetPixel(0, 0);
// pixel will contain average values for entire orig Bitmap
byte avgR = pixel.R; // etc.
Basically, you use DrawImage to copy the original Bitmap into a 1-pixel Bitmap. The RGB values of that 1 pixel will then represent the averages for the entire original. GetPixel is relatively slow, but only when you use it on a large Bitmap, pixel-by-pixel. Calling it once here is no biggie.
基本上，您使用 DrawImage 将原始位图复制到 1 像素位图。该 1 个像素的 RGB 值将代表整个原件的平均值。GetPixel 相对较慢，但仅当您在大的 Bitmap 上逐个像素地使用它时。在这里调用一次没什么大不了的。
Using LockBits is indeed fast, but some Windows users have security policies that prevent the execution of "unsafe" code. I mention this because this fact just bit me on the behind recently.
使用 LockBits 确实很快，但一些 Windows 用户有防止执行“不安全”代码的安全策略。我之所以提到这一点，是因为这个事实最近让我感到不寒而栗。
Update: with InterpolationMode set to HighQualityBicubic, this method takes about twice as long as averaging with LockBits; with HighQualityBilinear, it takes only slightly longer than LockBits. So unless your users have a security policy that prohibits unsafecode, definitely don't use my method.
更新：将 InterpolationMode 设置为 HighQualityBicubic，此方法所需的时间大约是 LockBits 平均的两倍；使用 HighQualityBilinear，它只需要比 LockBits 稍长的时间。所以除非你的用户有禁止unsafe代码的安全策略，否则绝对不要使用我的方法。
Update 2:with the passage of time, I now realize why this approach doesn't work at all. Even the highest-quality interpolation algorithms incorporate only a few neighboring pixels, so there's a limit to how much an image can be squashed down without losing information. And squashing a image down to one pixel is well beyond this limit, no matter what algorithm you use.
更新 2：随着时间的推移，我现在意识到为什么这种方法根本不起作用。即使是最高质量的插值算法也只包含几个相邻的像素，因此在不丢失信息的情况下压缩图像的程度是有限的。无论您使用什么算法，将图像压缩到一个像素都远远超出了这个限制。
The only way to do this would be to shrink the image in steps (maybe shrinking it by half each time) until you get it down to the size of one pixel. I can't express in mere words what an utter waste of time writing something like this would be, so I'm glad I stopped myself when I thought of it. :)
做到这一点的唯一方法是逐步缩小图像（可能每次缩小一半），直到将其缩小到一个像素的大小。我无法用单纯的语言来表达写这样的东西是多么浪费时间，所以我很高兴我一想到它就停下来了。:)
Please, nobody vote for this answer any more - it might be my stupidest idea ever.
拜托，没有人再投票给这个答案了——这可能是我有史以来最愚蠢的想法。
