How to Modify the Pixels of a Bitmap Source

This topic demonstrates how to modify the pixels of a bitmap source using the IWICBitmap and IWICBitmapLock components.

To modify the pixels of a bitmap source

1. Create an IWICImagingFactory object to create Windows Imaging Component (WIC) objects.

   // Create WIC factory
   hr = CoCreateInstance(
       CLSID_WICImagingFactory,
       NULL,
       CLSCTX_INPROC_SERVER,
       IID_PPV_ARGS(&m_pIWICFactory)
       );
   

2. Use the CreateDecoderFromFilename method to create an IWICBitmapDecoder from an image file.

   HRESULT hr = S_OK;
   
   IWICBitmapDecoder *pIDecoder = NULL;
   IWICBitmapFrameDecode *pIDecoderFrame  = NULL;
   
   hr = m_pIWICFactory->CreateDecoderFromFilename(
      L"turtle.jpg",                  // Image to be decoded
      NULL,                           // Do not prefer a particular vendor
      GENERIC_READ,                   // Desired read access to the file
      WICDecodeMetadataCacheOnDemand, // Cache metadata when needed
      &pIDecoder                      // Pointer to the decoder
      );
   

3. Get the first IWICBitmapFrameDecode of the image.

   // Retrieve the first bitmap frame.
   if (SUCCEEDED(hr))
   {
      hr = pIDecoder->GetFrame(0, &pIDecoderFrame);
   }
   

   The JPEG file format only supports a single frame. Because the file in this example is a JPEG file, the first frame (0) is used. For image formats that have multiple frames, see How to Retrieve the Frames of an Image for accessing each frame of the image.

4. Create an IWICBitmap from the previously obtained image frame.

   IWICBitmap *pIBitmap = NULL;
   IWICBitmapLock *pILock = NULL;
   
   UINT uiWidth = 10;
   UINT uiHeight = 10;
   
   WICRect rcLock = { 0, 0, uiWidth, uiHeight };
   
   // Create the bitmap from the image frame.
   if (SUCCEEDED(hr))
   {
      hr = m_pIWICFactory->CreateBitmapFromSource(
         pIDecoderFrame,          // Create a bitmap from the image frame
         WICBitmapCacheOnDemand,  // Cache bitmap pixels on first access
         &pIBitmap);              // Pointer to the bitmap
   }
   

5. Obtain an IWICBitmapLock for a specified rectangle of the IWICBitmap.

   if (SUCCEEDED(hr))
   {
      // Obtain a bitmap lock for exclusive write.
      // The lock is for a 10x10 rectangle starting at the top left of the
      // bitmap.
      hr = pIBitmap->Lock(&rcLock, WICBitmapLockWrite, &pILock);
   

6. Process the pixel data that is now locked by the IWICBitmapLock object.

      if (SUCCEEDED(hr))
      {
         UINT cbBufferSize = 0;
         BYTE *pv = NULL;
   
         // Retrieve a pointer to the pixel data.
         if (SUCCEEDED(hr))
         {
            hr = pILock->GetDataPointer(&cbBufferSize, &pv);
         }
   
         // Pixel manipulation using the image data pointer pv.
         // ...
   
         // Release the bitmap lock.
         SafeRelease(&pILock);
      }
   }
   

   To unlock the IWICBitmap, call IUnknown::Release on all IWICBitmapLock objects associated with the IWICBitmap.

7. Clean up created objects.

   SafeRelease(&pIBitmap);
   SafeRelease(&pIDecoder);
   SafeRelease(&pIDecoderFrame);
   

See Also

Programming Guide

Reference

Samples