Recipe 10.21. Full Listing of the LockImage Class

Sample code folder: Chapter 10\LockImage

This recipe contains the full code for the LockImage class described in Recipes 10.18, 10.19 through 10.20:

 Imports System.Drawing.Imaging Imports System.Runtime.InteropServices.Marshal Public Class LockImage    Private BaseImage As Bitmap    Private BaseImageWidth As Integer    Private BaseImageHeight As Integer    Private TotalPixels As Integer    Private ImageAddress As IntPtr    Private ImageContent As BitmapData    Private ImageBuffer( ) As Integer    Public Property Image( ) As Bitmap       ' ----- User access to the relevant image.       Get          Return BaseImage       End Get       Set(ByVal Value As Bitmap)          Dim canvas As Graphics          BaseImage = New Bitmap(Value.Width, _             Value.Height, Value.PixelFormat)          canvas = Graphics.FromImage(BaseImage)          canvas.DrawImage(Value, 0, 0, _             Value.Width, Value.Height)          canvas.Dispose( )       End Set    End Property    Private Sub LockTheImage( )       ' ----- Lock the image in memory. How much room       '       do we need?       BaseImageWidth = BaseImage.Width       BaseImageHeight = BaseImage.Height       TotalPixels = BaseImageWidth * BaseImageHeight       ' ----- Create a stable (locked) area in memory. It       '       will store 32-bit color images.       ReDim ImageBuffer(TotalPixels - 1)       ImageContent = BaseImage.LockBits( _          New Rectangle(0, 0, BaseImageWidth, _          BaseImageHeight), ImageLockMode.ReadWrite, _          PixelFormat.Format32bppRgb)       ImageAddress = ImageContent.Scan0       ' ----- Associate the buffer and the locked memory.       Copy(ImageAddress, ImageBuffer, 0, TotalPixels)    End Sub    Private Sub UnlockTheImage( )       ' ----- Unlock the memory area.       Copy(ImageBuffer, 0, ImageAddress, TotalPixels)       Image.UnlockBits(ImageContent)       ImageContent = Nothing       ReDim ImageBuffer(0)    End Sub    Public Sub MakeGray( )       ' ----- Make a grayscale version of the image.       Dim pixelIndex As Integer       Dim onePixel As Integer       Dim alphaPart As Integer       Dim redPart As Integer       Dim greenPart As Integer       Dim bluePart As Integer       Dim maxColor As Integer       Dim minColor As Integer       Dim down As Integer       Dim across As Integer       ' ----- Lock the image for speed.       LockTheImage( )       ' ----- Process each pixel in the grid.       For down = 0 To BaseImageHeight - 1          For across = 0 To BaseImageWidth - 1             ' ----- Locate the pixel's color.             pixelIndex = down * BaseImageWidth + across             onePixel = ImageBuffer(pixelIndex)             ' ----- Extract the color values.             alphaPart = (onePixel >> 24) And &HFF             redPart = (onePixel >> 16) And &HFF             greenPart = (onePixel >> 8) And &HFF             bluePart = onePixel And &HFF             ' ----- Get the general color intensity.             maxColor = Math.Max(redPart, Math.Max(greenPart, _                bluePart))             minColor = Math.Min(redPart, Math.Min(greenPart, _                bluePart))             onePixel = (maxColor + minColor) \ 2             ' ----- Use a common intensity for all colors.             bluePart = onePixel             greenPart = onePixel             redPart = onePixel             ' ----- Set the pixel to the new color. Retain             '       the original alpha channel.             ImageBuffer(pixelIndex) = (alphaPart << 24) + _                (redPart << 16) + (greenPart << 8) + bluePart          Next across       Next down       ' ----- Finished. Unlock the image.       UnlockTheImage( )    End Sub    Public Sub Mirror( )       ' ----- Make a left-to-right mirror image.       Dim pixelIndex1 As Integer       Dim pixelIndex2 As Integer       Dim holdPixel As Integer       Dim down As Integer       ' ----- Lock the image for speed.       LockTheImage( )       ' ----- Process each row of the image.       For down = 0 To BaseImageHeight - 1          ' ----- Process each column, up to halfway across.          pixelIndex1 = down * BaseImageWidth          pixelIndex2 = pixelIndex1 + BaseImageWidth - 1          Do While pixelIndex1 < pixelIndex2             ' ----- Swap two pixels.             holdPixel = ImageBuffer(pixelIndex1)             ImageBuffer(pixelIndex1) = _                ImageBuffer(pixelIndex2)             ImageBuffer(pixelIndex2) = holdPixel             pixelIndex1 += 1             pixelIndex2 -= 1          Loop       Next down       ' ----- Finished. Unlock the image.       UnlockTheImage( )    End Sub    Public Sub EdgeDetect( )       ' ----- Enhance the edges within the image.       Dim onePixel As Integer       Dim redPart As Integer       Dim greenPart As Integer       Dim bluePart As Integer       Dim maxColor As Integer       Dim minColor As Integer       Dim down As Integer       Dim across As Integer       Dim pixArray(,) As Integer       Dim target(,) As Integer       Dim sumX As Integer       Dim sumY As Integer       Dim useSum As Integer       Dim squareX As Integer       Dim squareY As Integer       ' ----- Define the Sobel Edge Detector gradient       '       matrices.       Dim edgeX(,) = {{-1, 0, 1}, {-2, 0, 2}, {-1, 0, 1}}       Dim edgeY(,) = {{1, 2, 1}, {0, 0, 0}, {-1, -2, -1}}       ' ----- Lock the image for speed.       LockTheImage( )       ' ----- Convert the 1D pixel array to 2D for ease       '       of processing.       ReDim pixArray(BaseImageHeight - 1, BaseImageWidth - 1)       For down = 0 To BaseImageHeight - 1          For across = 0 To BaseImageWidth - 1             ' ----- Convert each pixel to a grayscale value.             onePixel = ImageBuffer(down * BaseImageWidth + _                across)             redPart = (onePixel >> 16) And &HFF             greenPart = (onePixel >> 8) And &HFF             bluePart = onePixel And &HFF             maxColor = Math.Max(redPart, Math.Max(greenPart, _                bluePart))              minColor = Math.Min(redPart, Math.Min(greenPart, _                bluePart))             pixArray(down, across) = (maxColor + minColor) \ 2          Next across       Next down       ' ----- Results will be placed in a second pixel array.       ReDim target(BaseImageHeight - 1, BaseImageWidth - 1)       ' ----- Process for edge detection.       For down = 0 To BaseImageHeight - 1          For across = 0 To BaseImageWidth - 1             ' ----- Calculate the edge factor.             sumX = 0             sumY = 0             If (down = 0) Or _                   (down = (BaseImageHeight - 1)) Then                ' ----- Ignore true edges.                useSum = 0             ElseIf (across = 0) Or _                   (across = (BaseImageWidth - 1)) Then                ' ---- Ignore true edges.                useSum = 0             Else                ' ----- Summarize a small square around                '       the point.                For squareX = -1 To 1                   For squareY = -1 To 1                      sumX += pixArray(down + squareY, _                         across + squareX) * _                         edgeX(squareX + 1, squareY + 1)                      sumY += pixArray(down + squareY, _                         across + squareX) * _                         edgeY(squareX + 1, squareY + 1)                   Next squareY                Next squareX                ' ----- Force the value into the 0 to 255 range.                useSum = Math.Abs(sumX) + Math.Abs(sumY)                If (useSum < 0) Then useSum = 0                If (useSum > 255) Then useSum = 255                useSum = 255 - useSum                ' ----- Save it as a grayscale value in                '       the pixel.                target(down, across) = useSum + _                   (useSum << 8) + (useSum << 16)             End If          Next across       Next down       ' ----- Move results back into the locked pixels array.       For down = 0 To BaseImageHeight - 1          For across = 0 To BaseImageWidth - 1             ImageBuffer(down * BaseImageWidth + across) = _                target(down, across)          Next across       Next down       ' ----- Finished. Unlock the image.       UnlockTheImage( )    End Sub End Class