Fast image handling: Image to byte array, byte array to bitmap

If you are going to change the color of pixels fast, you need to convert the original bitmap to byte array. This byte array is one-dimensional. The structure of it is simple:

Position

first line, first pixel

first line, second pixel

first line, third pixel

.

.

.

second line, first pixel

second line, second pixel

second line, third pixel

.

.

.

color values

B     |     R     |     G

B     |     R     |     G

B     |     R     |     G

.

.

.

B     |     R     |     G

B     |     R     |     G

B     |     R     |     G

.

.

.

The picture size in bytes is the length of this array: size in bytes = bmpData.Stride * bmpData.Height

        //convert image to byte array
        
        public byte[] BitmapToByteArray(Bitmap img)      //img is the input image. Image width and height in pixels. PixelFormat is 24 bit per pixel in this case
        {
            BitmapData bmpData=img.LockBits(new Rectangle(0,0,img.Width,img.Height),ImageLockMode.ReadOnly,img.PixelFormat);    //define and lock the area of the picture with rectangle
            int pixelbytes =Image.GetPixelFormatSize(img.PixelFormat) / 8;     //for 24 bpp the value of pixelbytes is 3, for 32 bpp is 4, for 8 bpp is 1
            IntPtr ptr=bmpData.Scan0;      //this is a memory address, where the bitmap starts
            Int32 psize = bmpData.Stride * bmpData.Height;      // picture size in bytes
            byte[] byOut=new byte[psize];     //create the output byte array, which size is obviously the same as the input one

            System.Runtime.InteropServices.Marshal.Copy(ptr, byOut, 0, psize);      //this is a very fast method, which copies the memory content to byteOut array, but implemented for 24 bpp pictures only
            img.UnlockBits(bmpData);      //release the locked memory
            return byOut;      //  e finita la commedia
        }



        //convert byte array to bitmap
        
        public Bitmap ByteArrayToBitmap(byte[] byteIn, int imwidth, int imheight)     // byteIn the input byte array. Picture size should be known
        {
            Bitmap picOut=new Bitmap(imwidth,imheight,PixelFormat.Format24bppRgb);  //define the output picture
            BitmapData bmpData = picOut.LockBits(new Rectangle(0, 0, imwidth, imheight), ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);
            IntPtr ptr=bmpData.Scan0;
            Int32 psize =   bmpData.Stride*imheight;
            System.Runtime.InteropServices.Marshal.Copy(byteIn,0,ptr,psize);
            picOut.UnlockBits(bmpData);
            return picOut;      //  e finita la commedia
        }