摘要: 关于空间域图像处理算法框架，直方图处理，空间域滤波器算法框架的编程心得，使用GDI+(C++)
一，图像文件的读取
初学数字图像处理时，图像文件的读取往往是一件麻烦的事情，我们要面对各种各样的图像文件格式，如果仅用C++的fstream库那就必须了解各种图像编码格式，这对于初学图像处理是不太现实的，需要一个能帮助轻松读取各类图像文件的库。在Win32平台上GDI+(C++)是不错的选择，不光使用上相对于Win32 GDI要容易得多，而且也容易移植到.Net平台上的GDI+。
Gdiplus::Bitmap类为我们提供了读取各类图像文件的接口，Bitmap::LockBits方法产生的BitmapData类也为我们提供了高速访问图像文件流的途径。这样我们就可以将精力集中于图像处理算法的实现，而不用关心各种图像编码。具体使用方式请参考MSDN中GDI+文[来源：GameRes.com]档中关于Bitmap类和BitmapData类的说明。另外GDI+仅在Windows XP/2003上获得直接支持，对于Windows 2000必须安装相关DLL，或者安装有Office 2003，Visual Studio 2003 .Net等软件。
二，空间域图像处理算法框架
(1) 在空间域图像处理中，对于一个图像我们往往需要对其逐个像素的进行处理，对每个像素的处理使用相同的算法（或者是图像中的某个矩形部分）。即，对于图像f(x,y),其中0≤x≤M,0≤y≤N,图像为M*N大小，使用算法algo，则f(x,y) = algo(f(x,y))。事先实现一个算法框架，然后再以函数指针或函数对象(functor,即实现operator()的对象)传入算法，可以减轻编程的工作量。
如下代码便是一例:
#ifndef PROCESSALGO_H
#define PROCESSALGO_H
#include
#include
namespace nsimgtk
{
template
bool ProcessPixelsOneByOne(Gdiplus::Bitmap* const p_bitmap, Processor processor, unsigned int x, unsigned int y,
unsigned int width, unsigned int height)
{
if (p_bitmap == NULL)
{
return false;
}
if ((width + x > p_bitmap->GetWidth()) || (height + y >p_bitmap->GetHeight()))
{
return false;
}
Gdiplus::BitmapData bitmapData;
Gdiplus::Rect rect(x, y, width,height);
if (p_bitmap->LockBits(&rect, Gdiplus::ImageLockModeWrite, pixelFormat, &bitmapData) != Gdiplus::Ok)
{
return false;
}
pixelType *pixels = (pixelType*)bitmapData.Scan0;
for (unsigned int row=0; row { for (unsigned int col=0; col { processor(&pixels[col+row*bitmapData.Stride/sizeof(pixelType)]); } } if (p_bitmap->UnlockBits(&bitmapData) != Gdiplus::Ok) { return false; } return true; } } #endif ProcessPixelsOneByOne函数可以对图像中从(x,y)位置起始，width*height大小的区域进行处理。模板参数pixelType用于指定像素大小，例如在Win32平台上传入unsigned char即为8位，用于8阶灰度图。模板参数Processor为图像处理算法实现，可以定义类实现void operator(pixelType *)函数，或者传入同样接口的函数指针。 如下便是一些算法示例(说明见具体注释): #ifndef SPATIALDOMAIN_H #define SPATIALDOMAIN_H #include #include namespace nsimgtk { // 8阶灰度图的灰度反转算法 class NegativeGray8 { public: void operator()(unsigned char *const p_value) { *p_value ^= 0xff; } }; // 8阶灰度图的Gamma校正算法 class GammaCorrectGray8 { private: unsigned char d_s[256]; public: GammaCorrectGray8::GammaCorrectGray8(double c, double gamma); void operator()(unsigned char*const p_value) { *p_value = d_s[*p_value]; } }; // 8阶灰度图的饱和度拉伸算法 class ContrastStretchingGray8 { private: unsigned char d_s[256]; public: ContrastStretchingGray8::ContrastStretchingGray8(double a1, double b1, unsigned int x1, double a2, double b2, unsigned int x2, double a3, double b3); void operator()(unsigned char*const p_value) { *p_value = d_s[*p_value]; } }; // 8阶灰度图的位平面分割，构造函数指定位平面号 class BitPlaneSliceGray8 { private: unsigned char d_s[256]; public: BitPlaneSliceGray8(unsigned char bitPlaneNum); void operator()(unsigned char* const p_value) { *p_value = d_s[*p_value]; } }; } #endif // 上述类中各构造函数的实现代码，应该分在另一个文件中，此处为说明方便，一并列出 #include "SpatialDomain/spatialDomain.h" namespace nsimgtk { GammaCorrectGray8::GammaCorrectGray8(double c, double gamma) { double temp; for (unsigned int i=0; i<256; ++i) { temp = ceil(c * 255.0 * pow(double(i)/255.0, gamma)); d_s[i] = unsigned char(temp); } } ContrastStretchingGray8::ContrastStretchingGray8(double a1, double b1, unsigned int x1, double a2, double b2, unsigned int x2, double a3, double b3) { if (x1 > 255 || x2 > 255 || x1 > x1) { for (unsigned int i=0; i<256; ++i) d_s[i] = i; } else { double tmp; for (unsigned int i=0; i { tmp = ceil(a1*double(i)+b1); d_s[i] = (unsigned char)tmp; } for (unsigned int i=x1; i { tmp = ceil(a2*double(i)+b2); d_s[i] = (unsigned char)tmp; } for (unsigned int i=x2; i<256; ++i) { tmp = ceil(a3*double(i)+b3); d_s[i] = (unsigned char)tmp; } } } BitPlaneSliceGray8::BitPlaneSliceGray8(unsigned char bitPlaneNum) { unsigned char bitMaskArray[8] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 }; for (unsigned int i=0; i<256; ++i) { unsigned char tmp = i; tmp &= bitMaskArray[bitPlaneNum]; tmp = (tmp >> bitPlaneNum) * 255; d_s[i] = tmp; } } } (2) 直方图在GDI+1.0中没有获得支持，我们必须自行实现。直方图相关的处理在数字图像处理中占有重要地位，可以通过它获取图像灰度级的统计信息，且可以通过直方图进行一些重要的图像增强技术，如直方图均衡化，直方图规定化，基本全局门限等。 下面是获取8阶图像直方图的算法实现： namespace nsimgtk { bool GetHistogramNormalizeGray8(Gdiplus::Bitmap * const p_bitmap, float *histogramArray) { if (p_bitmap == NULL || histogramArray == NULL) { return false; } Gdiplus::BitmapData bitmapData; Gdiplus::Rect rect(0, 0, p_bitmap->GetWidth(), p_bitmap->GetHeight()); if (p_bitmap->LockBits(&rect, Gdiplus::ImageLockModeRead, PixelFormat8bppIndexed, &bitmapData) != Gdiplus::Ok) { return false; } unsigned char *pixels = (unsigned char*)bitmapData.Scan0; unsigned int histogram[256]; for (int i=0; i<256; ++i) { histogram[i] = 0; } for (unsigned int row=0; row { for (unsigned int col=0; col { ++histogram[pixels[col+row*bitmapData.Stride]]; } } const unsigned int totalPixels = p_bitmap->GetWidth() * p_bitmap->GetHeight(); for (int i=0; i<256; ++i) { histogramArray[i] = float(histogram[i]) / float(totalPixels); } if (p_bitmap->UnlockBits(&bitmapData) != Gdiplus::Ok) { return false; } return true; } } 在获取直方图后(即上面算法的第二个参数)，再将其作为参数传入下面的对象的构造函数，然后以该对象为仿函数传入ProcessPixelsOneByOne即可实现8阶图像直方图均衡化: #ifndef SPATIALDOMAIN_H #define SPATIALDOMAIN_H #include #include namespace nsimgtk { // 8阶灰度图的直方图均衡化 class HistogramEqualizationGray8 { private: unsigned char d_s[256]; public: HistogramEqualizationGray8(const float *const histogramArray); void operator()(unsigned char *const p_value) { *p_value = d_s[*p_value]; } }; } #endif ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// #include "SpatialDomain/spatialDomain.h" namespace nsimgtk { HistogramEqualizationGray8::HistogramEqualizationGray8(const float *const histogramArray) { if (histogramArray != NULL) { float sum = 0.0; for (int i=0; i<256; ++i) { sum += histogramArray[i]; d_s[i] = unsigned char(sum * 255); } } } } (3)空间域滤波器，滤波器是一个m*n大小的掩模，其中m,n均为大于1的奇数。滤波器逐像素地通过图像的全部或部分矩形区域，然后逐像素地对掩模覆盖下的像素使用滤波器算法获得响应，将响应赋值于当前像素即掩模中心像素，另外滤波器算法使用中将会涉及到图像边缘的问题，这可以对边缘部分掩模使用补零法补齐掩模下无像素值的区域，或者掩模的移动范围以不越出图像边缘的方式移动，当然这些处理方法都会给图像边缘部分带来不良效果，但是一般情况下，图像边缘部分往往不是我们关注的部分或者没有重要的信息。 下面的滤波器算法框架SpatialFilterAlgo即以补零法(zero-padding)实现: #ifndef SPATIALFILTER_H #define SPATIALFILTER_H #include #include #include #include #include #include namespace nsimgtk { template bool SpatialFilterAlgo(Gdiplus::Bitmap* const p_bitmap, FilterMask filterMask, unsigned int x, unsigned int y, unsigned int width, unsigned int height) { if (p_bitmap == NULL) { return false; } if ((width + x > p_bitmap->GetWidth()) || (height + y >p_bitmap->GetHeight())) { return false; } Gdiplus::BitmapData bitmapData; Gdiplus::Rect rect(x, y, width,height); if (p_bitmap->LockBits(&rect, Gdiplus::ImageLockModeWrite, pixelFormat, &bitmapData) != Gdiplus::Ok) { return false; } pixelType *pixels = (pixelType*)bitmapData.Scan0; const unsigned int m = filterMask.d_m; // mask's width const unsigned int n = filterMask.d_n; // mask's height std::vector // copy original bitmap to extended image with zero-padding method for (unsigned int row=0; row { for (unsigned int col=0; col { tmpImage[(col+m/2)+(row+n/2)*(bitmapData.Stride/sizeof(pixelType)+m-1)] = pixels[col+row*bitmapData.Stride/sizeof(pixelType)]; } } // process every pixel with filterMask for (unsigned int row=0; row { for (unsigned int col=0; col { // fill the "m*n" mask with the current pixel's neighborhood for (unsigned int i=0; i { for (unsigned int j=0; j { filterMask.d_mask[i*m+j] = tmpImage[(col+j)+(row+i)*(bitmapData.Stride/sizeof(pixelType)+m-1)]; } } // replace the current pixel with filter mask's response pixels[col+row*bitmapData.Stride/sizeof(pixelType)] = filterMask.response(); } } if (p_bitmap->UnlockBits(&bitmapData) != Gdiplus::Ok) { return false; } return true; } } #endif 其中模板参数FilterMask即为滤波掩模算法。通常的滤波算法有均值滤波器，可以模糊化图像，去除图形中的细节部分，使得我们可以关注图像中较为明显的部分，均值滤波器用于周期性噪声。中值滤波器用于图像中存在椒盐噪声也即脉冲噪声的情况下。另外有基于一阶微分的Sobel梯度算子和基于两阶微分的拉普拉斯算子，它们往往被用于边缘检测中。 下面是一些滤波器算法的具体实现，所以滤波器算法都应该实现pixelType response()函数以及有d_mask,d_m,d_n成员，这可以通过继承__filteMask类获得(不需要付出虚函数代价)。 #ifndef SPATIALFILTER_H #define SPATIALFILTER_H #include #include #include #include #include #include namespace nsimgtk { // 滤波器掩模的基类，提供掩模大小d_m,d_n，掩模覆盖下的m*n个像素值d_mask // others filterMask should inherit it template struct __filterMask { const unsigned int d_m; const unsigned int d_n; // image's pixels under the m*n filter mask std::vector // filter mask's width and heigh must be a odd, if not, it will plus one for the width or the height __filterMask(unsigned int m, unsigned int n) : d_m(m%2 ? m:m+1), d_n(n%2 ? n:n+1), d_mask(d_m*d_n) { } }; // 掩模权值为全1的均值滤波器 template class averagingFilterMaskSp : public __filterMask { public: averagingFilterMaskSp(unsigned int m, unsigned int n) : __filterMask { } pixelType response() { return std::accumulate(d_mask.begin(), d_mask.end(), 0) / (d_m * d_n); } }; // 可自定义掩模权值的均值滤波器 template class averagingFilterMask : public __filterMask { private: std::vector int d_weight_sum; // all weights' sum public: averagingFilterMask(unsigned int m, unsigned int n, const std::vector : __filterMask { if (weightVec.size() != d_mask.size()) { // if weight's size isn't equal to mask's size, it will change filter mask as a special filter mask d_weight.resize(d_mask.size(), 1); } d_weight_sum = std::accumulate(d_weight.begin(), d_weight.end(), 0); } pixelType response() { return std::inner_product(d_mask.begin(), d_mask.end(), d_weight.begin(), 0) / d_weight_sum; } }; // 中值滤波器 template class medianFilterMask : public __filterMask { public: medianFilterMask(unsigned int m, unsigned int n) : __filterMask { } pixelType response() { std::sort(d_mask.begin(), d_mask.end()); return d_mask[d_mask.size()/2]; } }; // 3*3拉普拉斯滤波器 // the mask is: [0 1 0 [0 -1 0 // 1 -5 1 or -1 5 -1 // 0 1 0] 0 -1 0] // if pixel's brightness is less than min, set it to min // if pixel's brightness is larger than max, set it to max template class laplacianFilter : public __filterMask { public: laplacianFilter() : __filterMask { } pixelType response() { int ret = (int)(5*(int)d_mask[4]) - ((int)d_mask[5]+d_mask[3]+d_mask[1]+d_mask[7]); if (ret < min) ret = min; if (ret > max) ret = max; return ret; } }; // 3*3Sobel滤波器 // the mask is: [-1 -2 -1 [-1 0 1 // 0 0 0 and -2 0 2 // 1 2 1] -1 0 1] // if pixel's brightness is larger than max, set it to max template class sobelFilter : public __filterMask { public: sobelFilter() : __filterMask { } pixelType response() { int ret = ::abs(d_mask[6]+2*d_mask[7]+d_mask[8]-d_mask[0]-2*d_mask[1]-d_mask[2]) + ::abs(d_mask[2]+2*d_mask[5]+d_mask[8]-d_mask[0]-2*d_mask[3]-d_mask[6]); if (ret > max) ret = max; return ret; } }; } #endif
