我已经编写了一些例程来使用3x3内核来锐化灰度图像,
-1 -1 -1
-1 9 -1
-1 -1 -1
以下代码在非FFT(空间域)卷积的情况下工作良好,但在基于FFT(频域)卷积的情况下不起作用。
输出图像似乎模糊。
我有几个问题:
(1)此例程无法生成所需的结果。它还会冻结该应用程序。
public static Bitmap ApplyWithPadding(Bitmap image, Bitmap mask)
{
if(image.PixelFormat == PixelFormat.Format8bppIndexed)
{
Bitmap imageClone = (Bitmap)image.Clone();
Bitmap maskClone = (Bitmap)mask.Clone();
/////////////////////////////////////////////////////////////////
Complex[,] cPaddedLena = ImageDataConverter.ToComplex(imageClone);
Complex[,] cPaddedMask = ImageDataConverter.ToComplex(maskClone);
Complex[,] cConvolved = Convolution.Convolve(cPaddedLena, cPaddedMask);
return ImageDataConverter.ToBitmap(cConvolved);
}
else
{
throw new Exception("not a grascale");
}
}
(2)此例程产生了良好的结果。但是,慢到地狱。
public static Bitmap Apply(Bitmap sourceBitmap)
{
Sharpen filter = new Sharpen();
BitmapData sourceData = sourceBitmap.LockBits(new Rectangle(0, 0,
sourceBitmap.Width, sourceBitmap.Height),
ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
byte[] pixelBuffer = new byte[sourceData.Stride * sourceData.Height];
byte[] resultBuffer = new byte[sourceData.Stride * sourceData.Height];
Marshal.Copy(sourceData.Scan0, pixelBuffer, 0, pixelBuffer.Length);
sourceBitmap.UnlockBits(sourceData);
double blue = 0.0;
double green = 0.0;
double red = 0.0;
int filterWidth = filter.FilterMatrix.GetLength(1);
int filterHeight = filter.FilterMatrix.GetLength(0);
int filterOffset = (filterWidth - 1) / 2;
int calcOffset = 0;
int byteOffset = 0;
for (int offsetY = filterOffset; offsetY < sourceBitmap.Height - filterOffset; offsetY++)
{
for (int offsetX = filterOffset; offsetX <
sourceBitmap.Width - filterOffset; offsetX++)
{
blue = 0;
green = 0;
red = 0;
byteOffset = offsetY *
sourceData.Stride +
offsetX * 4;
for (int filterY = -filterOffset;
filterY <= filterOffset; filterY++)
{
for (int filterX = -filterOffset;
filterX <= filterOffset; filterX++)
{
calcOffset = byteOffset +
(filterX * 4) +
(filterY * sourceData.Stride);
blue += (double)(pixelBuffer[calcOffset]) *
filter.FilterMatrix[filterY + filterOffset,
filterX + filterOffset];
green += (double)(pixelBuffer[calcOffset + 1]) *
filter.FilterMatrix[filterY + filterOffset,
filterX + filterOffset];
red += (double)(pixelBuffer[calcOffset + 2]) *
filter.FilterMatrix[filterY + filterOffset,
filterX + filterOffset];
}
}
blue = filter.Factor * blue + filter.Bias;
green = filter.Factor * green + filter.Bias;
red = filter.Factor * red + filter.Bias;
if (blue > 255)
{ blue = 255; }
else if (blue < 0)
{ blue = 0; }
if (green > 255)
{ green = 255; }
else if (green < 0)
{ green = 0; }
if (red > 255)
{ red = 255; }
else if (red < 0)
{ red = 0; }
resultBuffer[byteOffset] = (byte)(blue);
resultBuffer[byteOffset + 1] = (byte)(green);
resultBuffer[byteOffset + 2] = (byte)(red);
resultBuffer[byteOffset + 3] = 255;
}
}
Bitmap resultBitmap = new Bitmap(sourceBitmap.Width, sourceBitmap.Height);
BitmapData resultData = resultBitmap.LockBits(new Rectangle(0, 0,
resultBitmap.Width, resultBitmap.Height),
ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
Marshal.Copy(resultBuffer, 0, resultData.Scan0, resultBuffer.Length);
resultBitmap.UnlockBits(resultData);
return resultBitmap;
}
(3)以下是我的GUI代码。SharpenFilter.ApplyWithPadding()
如果我将图像用作遮罩,则可以正常工作。但是,如果我使用3
x3
内核,则不起作用。
string path = @"E:\lena.png";
string path2 = @"E:\mask.png";
Bitmap _inputImage;
Bitmap _maskImage;
private void LoadImages_Click(object sender, EventArgs e)
{
_inputImage = Grayscale.ToGrayscale(Bitmap.FromFile(path) as Bitmap);
/*
_maskImage = Grayscale.ToGrayscale(Bitmap.FromFile(path2) as Bitmap);
*/
SharpenFilter filter = new SharpenFilter();
double[,] mask = new double[,] { { -1, -1, -1, },
{ -1, 9, -1, },
{ -1, -1, -1, }, };
_maskImage = ImageDataConverter.ToBitmap(mask);
inputImagePictureBox.Image = _inputImage;
maskPictureBox.Image = _maskImage;
}
Bitmap _paddedImage;
Bitmap _paddedMask;
private void padButton_Click(object sender, EventArgs e)
{
Bitmap lena = Grayscale.ToGrayscale(_inputImage);
Bitmap mask = Grayscale.ToGrayscale(_maskImage);
////Not working...
//int maxWidth = (int)Math.Max(lena.Width, mask.Width);
//int maxHeight = (int)Math.Max(lena.Height, mask.Height);
////This is working correctly in case if I use a png image as a mask.
int maxWidth = (int)Tools.ToNextPow2(Convert.ToUInt32(lena.Width + mask.Width));
int maxHeight = (int)Tools.ToNextPow2(Convert.ToUInt32(lena.Height + mask.Height));
_paddedImage = ImagePadder.Pad(lena, maxWidth, maxHeight);
_paddedMask = ImagePadder.Pad(mask, maxWidth, maxHeight);
paddedImagePictureBox.Image = _paddedImage;
paddedMaskPictureBox.Image = _paddedMask;
}
private void filterButton_Click(object sender, EventArgs e)
{
// Not working properly.
// Freezes the application.
Bitmap sharp = SharpenFilter.ApplyWithPadding(_paddedImage, _paddedMask);
////Works well. But, very slow.
//Bitmap sharp = SharpenFilter.Apply(_paddedImage);
filteredPictureBox.Image = sharp as Bitmap;
}
输出:
源代码 :
主要问题似乎在于将内核解释为由无符号字节值组成的映像。结果,这些-1
值被转换为255
有效地计算与内核的卷积
255 255 255
255 9 255
255 255 255
可以从“卷积内核”图像中的白色区域立即观察到这一点。因此,所得的核是低通滤波器的核,从而产生相应的模糊效果。
解决此问题的最佳方法可能是将内核读取为带符号值的矩阵,而不是图像。
如果您仍然希望将内核作为映像处理,则需要将映像转换回带符号的值。我可以想到的最简单的方法是创建一个ImageDataConverter.ToInteger(Bitmap)
将字节映射到带符号的值的修改版本:
public static Complex[,] Unwrap(Bitmap bitmap)
{
int Width = bitmap.Width;
int Height = bitmap.Height;
Complex[,] array2D = new Complex[bitmap.Width, bitmap.Height];
...
else// If there is only one channel:
{
iii = (int)(*address);
if (iii >= 128)
{
iii -= 256;
}
}
Complex tempComp = new Complex((double)iii, 0.0);
array2D[x, y] = tempComp;
然后,您可以使用以下方法转换图像SharpenFilter.ApplyWithPadding
:
Complex[,] cPaddedMask = ImageDataConverter.Unwrap(maskClone);
然后,这应该给您以下结果:
虽然这可以提高图像的清晰度,但是您应该立即注意到图像比原始图像要暗得多。这是由于该Convolution.Rescale
功能可以根据图像的最小值和最大值动态地重新缩放图像。这可以方便地显示具有最大动态范围的图像,但可能导致与标准卷积不同的整体缩放比例。要实现此标准缩放(基于FFT实现的缩放),可以使用以下实现:
//Rescale values between 0 and 255.
private static void Rescale(Complex[,] convolve)
{
int imageWidth = convolve.GetLength(0);
int imageHeight = convolve.GetLength(1);
double scale = imageWidth * imageHeight;
for (int j = 0; j < imageHeight; j++)
{
for (int i = 0; i < imageWidth; i++)
{
double re = Math.Max(0, Math.Min(convolve[i, j].Real * scale, 255.0));
double im = Math.Max(0, Math.Min(convolve[i, j].Imaginary * scale, 255.0));
convolve[i, j] = new Complex(re, im);
}
}
}
然后,这应该为您提供具有更适当亮度级别的图像:
最后,对于滤波操作,通常会期望结果与原始图像大小匹配(与包括尾部的卷积不同)。通过以下方式裁剪结果SharpenFilter.ApplyWithPadding
:
...
// -3 terms are due to kernel size
// +5 vertical offset term is due to vertical reflection & offset in SetPixel
Rectangle rect = new Rectangle((cPaddedLena.GetLength(0) / 2 - 3) / 2,
(cPaddedLena.GetLength(1) / 2 - 3) / 2 + 5,
cPaddedLena.GetLength(0) / 2,
cPaddedLena.GetLength(1) / 2);
return ImageDataConverter.ToBitmap(cConvolved).Clone(rect, PixelFormat.Format8bppIndexed);
应该给你:
为了便于视觉比较,以下是原始图像:
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