如何将此方法与Bitmap并行化 [英] How do I parallelize this method with Bitmap
问题描述
我尝试在本文中并行化序列代码
语言学：C＃中的简单实现 [ ^ ]
我知道如何使用Parallel.For，但在这种情况下，我需要在循环内返回值（Bitmap对象）。有3个嵌套和一些if。
下面我发布了序列和修改后的并行代码以及关于该返回的2个错误。
< b>以下是错误：
错误2无法将匿名方法转换为委托类型'System.Action< long，system.threading.tasks.parallelloopstate>'因为某些返回类型在块中不能隐式转换为委托返回类型。
错误1因为'System.Action< long，system.threading.tasks.parallelloopstate>'返回void ，一个return关键字后面不能跟一个对象表达式。
有人可以帮我这个吗？我会非常感激，因为我不知道该怎么办：/
这是原作序列码：
Hi,
I try to parallelize sequence code in this article
Steganography: Simple Implementation in C#[^]
I know how to use Parallel.For, but in this case, I need return value (Bitmap object) inside the loop. There is 3 nested for and some if.
Below I post both sequence and modified parallel code and 2 errors regarding that return.
Here are the errors:
Error 2 Cannot convert anonymous method to delegate type 'System.Action<long,system.threading.tasks.parallelloopstate>' because some of the return types in the block are not implicitly convertible to the delegate return type.
Error 1 Since 'System.Action<long,system.threading.tasks.parallelloopstate>' returns void, a return keyword must not be followed by an object expression.
Can someone help me with this? I would be very grateful, because I don't know what to do with it :/
Here is the original sequence code:
public static Bitmap embedText(string text, Bitmap bmp)
{
State s = State.hiding;
int charIndex = 0;
int charValue = 0;
long colorUnitIndex = 0;
int zeros = 0;
int R = 0, G = 0, B = 0;
for (int i = 0; i < bmp.Height; i++)
{
for (int j = 0; j < bmp.Width; j++)
{
Color pixel = bmp.GetPixel(j, i);
pixel = Color.FromArgb(pixel.R - pixel.R % 2,
pixel.G - pixel.G % 2, pixel.B - pixel.B % 2);
R = pixel.R; G = pixel.G; B = pixel.B;
for (int n = 0; n < 3; n++)
{
if (colorUnitIndex % 8 == 0)
{
if (zeros == 8)
{
if ((colorUnitIndex - 1) % 3 < 2)
{
bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
}
return bmp;
}
if (charIndex >= text.Length)
{
s = State.filling_with_zeros;
}
else
{
charValue = text[charIndex++];
}
}
switch (colorUnitIndex % 3)
{
case 0:
{
if (s == State.hiding)
{
R += charValue % 2;
charValue /= 2;
}
} break;
case 1:
{
if (s == State.hiding)
{
G += charValue % 2;
charValue /= 2;
}
} break;
case 2:
{
if (s == State.hiding)
{
B += charValue % 2;
charValue /= 2;
}
bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
} break;
}
colorUnitIndex++;
if (s == State.filling_with_zeros)
{
zeros++;
}
}
}
}
return bmp;
}
并修改了并行版本的代码：
And there is modified code to parallel version:
public static Bitmap embedText(string text, Bitmap bmp)
{
State s = State.hiding;
int charIndex = 0;
int charValue = 0;
long colorUnitIndex = 0;
int zeros = 0;
int R = 0, G = 0, B = 0;
Parallel.For (0, bmp.Height, delegate(int i)
{
Parallel.For (0, bmp.Width, delegate(int j)
{
Color pixel = bmp.GetPixel(j, i);
pixel = Color.FromArgb(pixel.R - pixel.R % 2,
pixel.G - pixel.G % 2, pixel.B - pixel.B % 2);
R = pixel.R; G = pixel.G; B = pixel.B;
for (int n = 0; n < 3; n++)
{
if (colorUnitIndex % 8 == 0)
{
if (zeros == 8)
{
if ((colorUnitIndex - 1) % 3 < 2)
{
bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
}
return bmp; return bmp; //In this line is both 2 errors
}
if (charIndex >= text.Length)
{
s = State.filling_with_zeros;
}
else
{
charValue = text[charIndex++];
}
}
switch (colorUnitIndex % 3)
{
case 0:
{
if (s == State.hiding)
{
R += charValue % 2;
charValue /= 2;
}
} break;
case 1:
{
if (s == State.hiding)
{
G += charValue % 2;
charValue /= 2;
}
} break;
case 2:
{
if (s == State.hiding)
{
B += charValue % 2;
charValue /= 2;
}
bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
} break;
}
colorUnitIndex++;
if (s == State.filling_with_zeros)
{
zeros++;
}
}
}
});
return bmp;
}
推荐答案
请不要使用GetPixel来代替并行化 / SetPixel;这些方法非常慢，只能用于获取或设置很少的像素。相反，锁定位并在内存中处理它们：
http://msdn.microsoft.com/en-us/library/system.drawing.bitmap.lockbits%28v=vs.110%29.aspx [ ^ ]。
有关代码示例的第一种方法，请参阅文档页面。
-SA
Instead of "parallelizing" the way you do, don't useGetPixel/SetPixel; these methods are prohibitively slow and can only be used to get or set very few pixels. Instead, lock bit and process them in memory:
http://msdn.microsoft.com/en-us/library/system.drawing.bitmap.lockbits%28v=vs.110%29.aspx[^].
See the documentation page for the first of these two methods for code sample.
—SA
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