图片缩放算法实现与应用

引用工具地址：http://www.codeproject.com/Articles/146/Two-Pass-Scaling-using-Filters

Unlike traditional scaling of images, where every n'th pixel is sampled and copied to the result image, this template provides much more accurate image scaling features.

It takes a buffer of RGB values (as COLORREFs) and creates another buffer with new dimensions. The input / output buffers are sequential pixels (not compressed) compatible with the format used in 24-bit DIBs.

The template is instantiated with a specific filter. The filter determines the quality of the output image. Different basic filters are supplied with this template and additional filters can be easily added.

Major features:

• Provides professional quality image scaling.
• Code is optimized for image quality, not speed.
• Supports various image filters:
  • Box filter.
  • Bilinear filter.
  • Gaussian filter.
  • Hamming filter.
  • Blackman filter.
  • ...New filters can be easily added.
• Supports both magnification and minification.
• Does not force aspect ratio limitations. e.g. an image can be magnified horizontally and minified vertically.
• Supports 24-bit images. With little change can support other image formats / depths.
• Template based - no need for libraries, DLLs etc. No linkage problems.

How to use the scaling template:

Assuming you have a non-compressed true-color 24-bit DIB in memory (the bits array is pointed by m_pBits), where the original bitmap width is m_dwWidth and height is m_dwHeight.

Your code should look something like this:

1. #include <2PassScale.h>
   ...
   void CMyDIB::ScaleTo (DWORD dwNewWidth, DWORD dwNewHeight)
   {
       C2PassScale <CBilinearFilter> ScaleEngine;
       COLORREF *pOldBitmap = m_pBits;
       m_pBits = ScaleEngine.AllocAndScale (   m_pBits,
                                               m_dwWidth,
                                               m_dwHeight,
                                               dwNewWidth,
                                               dwNewHeight
                                           );
       if (NULL == m_pBits)
       {
           //
           // Handle errors here
           //
       }
       m_dwWidth = dwNewWidth;
       m_dwHeight = dwNewHeight;
       delete pOldBitmap;
   }
   //
   // Alternatively, if you already have a pre-allocated destination buffer
   // in the new size you can call ScaleEngine.Scale (...) and give it that buffer
   //

   通过模板的方式，可以轻松比较各种图片缩放方法。