A detailed description of grayscale technology in C #

Last year bought this Digital image processing algorithm, has not seen, the first few weeks have been busy working on the work, take advantage of this stage leisurely, play a picture processing, this thing is still very interesting.

Before we do the user registration on the web, usually do a verification code, we all know to prevent violent registration, of course, mention the verification code we all know C # inside there is a bitmap class specifically used to deal with the picture, OK, this one from the simplest "image grayscale" speaking.

One: Image grayscale

As we all know, bitmaps are made up of a single pixel point, which may be red, orange, pink, and so on, which we all know are represented by RGB.

Each color component is a byte (0-255), so the average pixel point is 24 bits, of course there are 32 bits, 64 bits, when RGB is a different value between 0-255, then the pixel is rendered "colorful", and when RGB is the same value is, then the pixel is rendered "gray", If you have played CSS, you must know that giving a font color is usually #999999, #666666, #333333这些不同深度的灰色.

1. Calculation formula

How do we set a reasonable grayscale value? Of course, use the current RGB as a template, and then multiply the RGB by a reasonable weight is OK

The code is as follows:

Gary (i,j) =0.299*r (i,j) +0.587*g (i,j) +0.114*b (I,J);

2. Programming

With the formula, it is no problem to realize it. There is a getpixel/setpixel in the bitmap class that can get and set the current pixel point.

static void Main (string[] args) {  Bitmap Bitmap = new Bitmap (environment.currentdirectory + "//1.jpg");  for (int i = 0; i < bitmap. Width; i++)  {for    (int j = 0; J < bitmap. Height; J + +)    {      //Take picture the current pixel point      var color = bitmap. GetPixel (i, j);      var gray = (int) (color. R * 0.299 + color. G * 0.587 + color. B * 0.114);      Re-sets the current pixel point      bitmap. SetPixel (i, J, Color.FromArgb (Gray, Gray, Gray));    }  }  Bitmap. Save (environment.currentdirectory + "//2.jpg");}

3. Improvements

The above method is very simple, get/set is OK, of course, this is our point of view of the pixel point to consider the problem, it seems as long as O (N2) time can KO problem, but Get/set is far from O (1), based on performance considerations, we can have better methods, At this point we can stand in the perspective of the byte, but here we have to pay attention to a problem is: width=21px, a pixel occupies 3 bytes, but 21 pixels does not necessarily occupy 63 bytes, because the system based on performance considerations, in each row is stored in a "unused area", To make sure that the number of bytes in each row of a picture is a multiple of 4, how do you read the number of bits in a row?

C # There is a stride attribute that can be used to get it, very simple.

static void Main (string[] args) {Bitmap Bitmap = new Bitmap (environment.currentdirectory + "//1.jpg"); Defines a specified range of bounds for a rect that locks bitmap Rectangle rect = new Rectangle (0, 0, bitmap. Width, Bitmap.      Height); Add lock area pixel var bitmapData = bitmap. LockBits (Rect, Imagelockmode.readwrite, bitmap.      PixelFormat);      The first address of the bitmap is var ptr = bitmapdata.scan0; Stride: Scan line int len = bitmapdata.stride * Bitmap.      Height;      var bytes = new Byte[len];      The pixel value of the locked area is copied to the byte array in marshal.copy (PTR, bytes, 0, Len); for (int i = 0; i < bitmap. Height; i++) {for (int j = 0; J < bitmap. Width * 3; j = j + 3) {var color = bytes[i * Bitmapdata.stride + j + 2] * 0.299 + bytes[i * bitmapdat          A.stride + j + 1] * 0.597 + bytes[i * bitmapdata.stride + j] * 0.114; Bytes[i * bitmapdata.stride + j] = Bytes[i * Bitmapdata.stride + j + 1] = Bytes[i * BitmapData . Stride + j + 2] = (byte) COLor      }}//copy back to bitmap marshal.copy (bytes, 0, PTR, Len); Unlock bitmap.      Unlockbits (BitmapData); Bitmap.    Save (environment.currentdirectory + "//3.jpg"); }

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A detailed description of grayscale technology in C #

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A detailed description of grayscale technology in C #