[英]How to speed up this calculation
Given two ARGB colors represented as integers, 8 bit/channel (alpha, red, green, blue), I need to compute a value that represents a sort of distance (also integer) between them. 鉴于两个ARGB颜色表示为整数,8位/通道(alpha,红色,绿色,蓝色),我需要计算一个值,表示它们之间的一种距离(也是整数)。
So the formula for the distance is: Delta=|R1-R2|+|G1-G2|+|B1-B2|
因此距离的公式为:
Delta=|R1-R2|+|G1-G2|+|B1-B2|
where Rx, Gx and Bx are the values of the channles of color 1 and 2. Alpha channel is always ignored. 其中Rx,Gx和Bx是颜色1和2的通道值.Alpha通道始终被忽略。
I need to speed up this calculation because is done a lot of times on a slow machine. 我需要加快这个计算速度,因为在慢速机器上进行了很多次。 What is the 'geekies' way to calculate this on a single thread given the two integers.
在给定两个整数的情况下,在单个线程上计算这个的'geekies'方法是什么。
My best so far is but I guess this can be improved further: 到目前为止,我最好的是,但我想这可以进一步改进:
//Used for color conversion from/to int
private const int ChannelMask = 0xFF;
private const int GreenShift = 8;
private const int RedShift = 16;
public int ComputeColorDelta(int color1, int color2)
{
int rDelta = Math.Abs(((color1 >> RedShift) & ChannelMask) - ((color2 >> RedShift) & ChannelMask));
int gDelta = Math.Abs(((color1 >> GreenShift) & ChannelMask) - ((color2 >> GreenShift) & ChannelMask));
int bDelta = Math.Abs((color1 & ChannelMask) - (color2 & ChannelMask));
return rDelta + gDelta + bDelta;
}
Long Answer: 答案很长:
How many is "a lot" 有多少是“很多”
I have a fast machine I guess, but I wrote this little script: 我想有一台快速的机器,但我写了这个小脚本:
public static void Main() {
var s = Stopwatch.StartNew();
Random r = new Random();
for (int i = 0; i < 100000000; i++) {
int compute = ComputeColorDelta(r.Next(255), r.Next(255));
}
Console.WriteLine(s.ElapsedMilliseconds);
Console.ReadLine();
}
And the output is: 6878 输出是:6878
So 7 seconds for 100 million times seems pretty good. 所以7亿次1亿次看起来相当不错。
We can definitely speed this up though. 我们绝对可以加快速度。 I changed your function to look like this:
我改变你的功能看起来像这样:
public static int ComputeColorDelta(int color1, int color2) {
return 1;
}
With that change, the output was: 5546. So, we managed to get a 1 second performance gain over 100 million iterations by returning a constant. 随着这一变化,输出为:5546。因此,通过返回常量,我们设法获得超过1亿次迭代的1秒性能增益。 ;)
;)
Short answer: this function is not your bottleneck. 简短回答:这个功能不是你的瓶颈。 :)
:)
I'm trying to let runtime to make calculation for me. 我正试图让运行时为我计算。
First of all I define struct with explicit field offset 首先,我使用显式字段偏移定义struct
[StructLayout(LayoutKind.Explicit)]
public struct Color
{
[FieldOffset(0)] public int Raw;
[FieldOffset(0)] public byte Blue;
[FieldOffset(8)] public byte Green;
[FieldOffset(16)] public byte Red;
[FieldOffset(24)] public byte Alpha;
}
the calculation function will be: 计算功能将是:
public int ComputeColorDeltaOptimized(Color color1, Color color2)
{
int rDelta = Math.Abs(color1.Red - color2.Red);
int gDelta = Math.Abs(color1.Green - color2.Green);
int bDelta = Math.Abs(color1.Blue - color2.Blue);
return rDelta + gDelta + bDelta;
}
And the usage 和用法
public void FactMethodName2()
{
var s = Stopwatch.StartNew();
var color1 = new Color(); // This is a structs, so I can define they out of loop and gain some performance
var color2 = new Color();
for (int i = 0; i < 100000000; i++)
{
color1.Raw = i;
color2.Raw = 100000000 - i;
int compute = ComputeColorDeltaOptimized(color1, color2);
}
Console.WriteLine(s.ElapsedMilliseconds); //5393 vs 7472 of original
Console.ReadLine();
}
One idea would be to use the same code you already have, but in a different order: apply the mask, take the difference, then shift. 一个想法是使用您已有的相同代码,但顺序不同:应用掩码,取差异,然后移动。
Another modification that might help is to inline this function: that is, instead of calling it for each pair of colors, just compute the difference directly, inside whatever loop executes this code. 可能有帮助的另一个修改是内联这个函数:也就是说,不是为每对颜色调用它,而是直接计算差异,在任何循环中执行此代码。 I assume it is inside a tight loop, because otherwise its cost would be negligible.
我认为它是在一个紧凑的循环内,因为否则它的成本可以忽略不计。
Lastly, since you're probably getting image pixel data, you'd save a lot by going the unsafe
route: make your bitmaps like this EditableBitmap , then grab the byte* and read the image data out of it. 最后,由于您可能正在获取图像像素数据,因此通过使用
unsafe
路径可以节省很多:使您的位图像这个EditableBitmap ,然后获取字节*并从中读取图像数据。
You can do this in order to reduce the AND operations: 您可以这样做以减少AND操作:
public int ComputeColorDelta(int color1, int color2)
{
int rDelta = Math.Abs((((color1 >> RedShift) - (color2 >> RedShift))) & ChannelMask)));
// same for other color channels
return rDelta + gDelta + bDelta;
}
not much but something... 不多但是......
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