GDI+白色背景的 JPG 的 DrawImage 不是白色的

发布于 2024-10-10 00:31:49 字数 1294 浏览 0 评论 0原文

我正在使用 GDI+ 在 C++ CWnd 窗口中显示 JPG。 JPG 具有纯白色背景 0xffffff，但使用graphics.DrawImage 显示时，背景为灰白色，混合有 0xfff7f7、0xf7fff7、0xf7f7f7 等像素颜色。下面是代码，我尝试了各种设置，例如CompositingMode、SmoothingMode等。图像没有缩放。

奇怪的是，背景颜色根据图像中的其他非白色内容而不同。如果我制作一个简单的全白色 JPG，那么它就可以工作，甚至可以制作大部分白色，只有一些黑色文本。图像比较如下所示。


  CClientDC dc(this);
  Gdiplus::Graphics graphics(dc);

  Gdiplus::Bitmap* bmp = Gdiplus::Bitmap::FromFile( L"c:\\test.jpg" );
  graphics.SetInterpolationMode(Gdiplus::InterpolationModeHighQuality); 
  //graphics.SetCompositingQuality(Gdiplus::CompositingQualityHighQuality); 
  graphics.SetCompositingQuality(Gdiplus::CompositingQualityDefault); 
  graphics.SetCompositingMode(Gdiplus::CompositingModeSourceCopy); 
  //graphics.SetSmoothingMode( Gdiplus::SmoothingMode::SmoothingModeDefault );
  graphics.DrawImage(bmp, 0, 0, bmp->GetWidth(), bmp->GetHeight() );

在这里，我仅在图像的左侧有文本和一些混合（没有 Alpha，这是 JPG）。右边的一切都是纯白色的。你可以看到背景全是灰色的。

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这里我开始删除内部内容（仅在左侧）。在某一点之后，整个背景开始显示白色。 ???

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在开始显示白色之前删除图像区域的哪一部分并不重要，只要我删除其中的很大一部分。 png 也会发生同样的情况。

这是原始的 test.jpg 图像...

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原文

I am displaying a JPG in a C++ CWnd window using GDI+. The JPG has a pure white background, 0xffffff, but when displayed using graphics.DrawImage, the background is off-white with a mix of pixel colors such as 0xfff7f7, 0xf7fff7, 0xf7f7f7. Below is the code, I have tried various settings such as CompositingMode, SmoothingMode, etc. The image is not scaled.

The weird thing is that the background color is different depending on other non-white content in the image. If I make a simple all white JPG, then it works, or even a mostly white with just some black text. Comparison of images are shown below.


  CClientDC dc(this);
  Gdiplus::Graphics graphics(dc);

  Gdiplus::Bitmap* bmp = Gdiplus::Bitmap::FromFile( L"c:\\test.jpg" );
  graphics.SetInterpolationMode(Gdiplus::InterpolationModeHighQuality); 
  //graphics.SetCompositingQuality(Gdiplus::CompositingQualityHighQuality); 
  graphics.SetCompositingQuality(Gdiplus::CompositingQualityDefault); 
  graphics.SetCompositingMode(Gdiplus::CompositingModeSourceCopy); 
  //graphics.SetSmoothingMode( Gdiplus::SmoothingMode::SmoothingModeDefault );
  graphics.DrawImage(bmp, 0, 0, bmp->GetWidth(), bmp->GetHeight() );

Here I have text and some blending only on the left side of the image (no alphas, this is JPG) . Everything to the right is pure white. You can see the background is all grey.

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Here I started removing the internal content (only on the left side). After a certain point the entire background starts displaying white. ???

alt text

It doesn't really matter which part of the image area I remove before it starts displaying white, as long as I remove a large portion of it. The same occurs for pngs.

Here is the original test.jpg image...

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∞梦里开花 2024-10-17 00:31:49

我正在用我找到的解决方案回答我的问题。在我的例子中，直接在传递的 HDC 上使用graphics.DrawImage 似乎存在一些问题。如果我使用内存 DC 进行初始绘图，然后在 HDC 上进行 BitBlt，那么它就可以工作。

我在 PNG 和透明度方面也遇到了一些问题。使用下面的解决方案，我也能够解决这个问题。我的 PNG 是使用 Bitmap::FromStream 从流加载的。 Alpha 通道丢失，我尝试使用 LockBits 进行不同的尝试，并使用 PixelFormat32bppARGB 重新创建位图以及克隆。我能够得到一些东西来工作（经过大量的努力和额外的代码），但它仍然存在我在这里问的灰色背景问题。

就我而言，透明区域有一个已知的纯色背景色。我使用 Bitmap.GetHBITMAP 并传递背景颜色。然后首先在内存 DC 上绘制位图。在这里我能够解决我的两个问题！


  Gdiplus::Bitmap* bmp = Gdiplus::Bitmap::FromFile( L"c:\test.jpg" )
  Gdiplus::Color backColor( 0xff, 0xff, 0xff );
  HBITMAP hBmp;
  bmp->GetHBITMAP( backColor, &hBmp );
  CDC     bitmapDC;
  bitmapDC.CreateCompatibleDC(hdc);  // pass original HDC for drawing
  HBITMAP oldBmp = bitmapDC.SelectBitmap(hBitmap);
  ::BitBlt( hdc, x, y, cx, cy, bitmapDC.m_hDC, 0, 0, SRCCOPY );
  bitmapDC.SelectBitmap(oldBmp);
  DeleteObject( hBmp );

如果有人知道，我会感兴趣为什么这可以解决问题。

I am answering my question with the solution that I found. It seems that using graphics.DrawImage directly on the passed HDC has some issues in my case. If I use a memory DC for the initial drawing, then BitBlt it on the HDC, then it works.

I also had some problems with PNG and transparency. Using the solution below, I was able to solve this problem as well. My PNG was loaded from a stream using Bitmap::FromStream. The alpha channel was lost and I was trying different attempts using LockBits and re-creating the bitmap with PixelFormat32bppARGB, as well as Cloning. I was able to get something to work (after a lot of effort and extra code), but it still had the grey background problem that I asked here.

In my case, I have a known solid background color for the transparent areas. I used Bitmap.GetHBITMAP and passed the background color. The bitmap was then drawn on the memory DC first. Here I was able to solve both of my problems!


  Gdiplus::Bitmap* bmp = Gdiplus::Bitmap::FromFile( L"c:\test.jpg" )
  Gdiplus::Color backColor( 0xff, 0xff, 0xff );
  HBITMAP hBmp;
  bmp->GetHBITMAP( backColor, &hBmp );
  CDC     bitmapDC;
  bitmapDC.CreateCompatibleDC(hdc);  // pass original HDC for drawing
  HBITMAP oldBmp = bitmapDC.SelectBitmap(hBitmap);
  ::BitBlt( hdc, x, y, cx, cy, bitmapDC.m_hDC, 0, 0, SRCCOPY );
  bitmapDC.SelectBitmap(oldBmp);
  DeleteObject( hBmp );

If anyone knows, I would be interested why this fixes the problem.

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