图像操作-缩略图的自动调整大小/裁剪
本文关键字：调整 裁剪 操作 略图 图像 | 更新日期: 2023-09-27 18:24:41
我用这个碰壁了。。。我知道我的缺陷在逻辑上，但我会解释我的处境。
我正在（尝试）编写代码，为Silverlight应用程序底部的导航栏动态创建一个方形（75x75）像素缩略图。当我调试下面的代码时，在缩放嵌套循环的过程中，我一直会得到一个"数组索引越界"错误（我只调试过srcWidth>srcHeight，一次一步）
我测试的源图像是307x162（49734像素）此操作的dest大小（每个当前逻辑）为150x75（11250像素）当然，在这之后，我打算将结果裁剪为75x75
在到达11251作为目的地索引之前，它只通过了源图像的一半。我知道这是我的逻辑，我只是不知道我用来建造目的地的尺寸是否出错了，或者在从铸造浮体到int所使用的近似中，或者它既不是
我不知道，这就是我在这里发帖的原因。。。不管怎样，这是我的来源：
private void ResizeNavBarImage(Image src)
{
const int SizeOfRGB = 4;
WriteableBitmap bmpSource = new WriteableBitmap((BitmapSource)src.Source);
int[] iSourcePixels = bmpSource.Pixels;
int srcWidth = bmpSource.PixelWidth;
int srcHeight = bmpSource.PixelHeight;
int destWidth = 75;
int destHeight = 75;
float xFactor = srcWidth / destWidth;
float yFactor = srcHeight / destHeight;
float xSource, ySource;
int iApprox;
int iIndex = 0;
if (srcWidth > srcHeight)
{
WriteableBitmap bmpDest = new WriteableBitmap((int)(destWidth * yFactor), destHeight);
int[] iDestPixels = bmpDest.Pixels;
// Resize srcHeight to destHeight, srcWidth to same ratio
for (int i = 0; i < srcHeight; i++)
{
for (int j = 0; j < srcWidth; j++)
{
xSource = j * yFactor;
ySource = i * yFactor;
iApprox = (int)(ySource * srcWidth + xSource);
iDestPixels[iIndex++] = iSourcePixels[iApprox];
}
}
// Crop half of difference from each side of the width
srcWidth = bmpDest.PixelWidth;
srcHeight = bmpDest.PixelHeight;
int xLeftOffset = (srcWidth - srcHeight) / 2;
WriteableBitmap bmpFinalDest = new WriteableBitmap(destWidth, destHeight);
for (int iPixelRow = 0; iPixelRow < destHeight; iPixelRow++)
{
int srcOffset = (iPixelRow * srcWidth + xLeftOffset) * SizeOfRGB;
int destOffset = iPixelRow * destWidth * SizeOfRGB;
Buffer.BlockCopy(bmpDest.Pixels, srcOffset, bmpFinalDest.Pixels, destOffset, destWidth * SizeOfRGB);
}
src.Source = (ImageSource)bmpFinalDest;
}
else if (srcWidth < srcHeight)
{
WriteableBitmap bmpDest = new WriteableBitmap(destWidth, (int)(destHeight * xFactor));
int[] iDestPixels = bmpDest.Pixels;
// Resize srcWidth to destWidth, srcHeight to same ratio
for (int i = 0; i < srcHeight; i++)
{
for (int j = 0; j < srcWidth; j++)
{
xSource = j * xFactor;
ySource = i * xFactor;
iApprox = (int)(ySource * srcWidth + xSource);
iDestPixels[iIndex++] = iSourcePixels[iApprox];
}
}
// Crop half of difference from each side of the height
srcWidth = bmpDest.PixelWidth;
srcHeight = bmpDest.PixelHeight;
int yTopOffset = (srcHeight - srcWidth) / 2;
WriteableBitmap bmpFinalDest = new WriteableBitmap(destWidth, destHeight);
for (int iPixelRow = yTopOffset; iPixelRow < (destHeight - (yTopOffset * 2)); iPixelRow++)
{
int srcOffset = iPixelRow * srcWidth * SizeOfRGB;
int destOffset = iPixelRow * destWidth * SizeOfRGB;
Buffer.BlockCopy(bmpDest.Pixels, srcOffset, bmpFinalDest.Pixels, destOffset, destWidth * SizeOfRGB);
}
src.Source = (ImageSource)bmpFinalDest;
}
else // (srcWidth == srcHeight)
{
WriteableBitmap bmpDest = new WriteableBitmap(destWidth, destHeight);
int[] iDestPixels = bmpDest.Pixels;
// Resize and set source
for (var i = 0; i < srcHeight; i++)
{
for (var j = 0; j < srcWidth; j++)
{
xSource = j * xFactor;
ySource = i * yFactor;
iApprox = (int)(ySource * srcWidth + xSource);
iDestPixels[iIndex++] = iSourcePixels[iApprox];
}
}
src.Source = (ImageSource)bmpDest;
}
}
=================================================
以下是我为子孙后代编写的工作代码（使用WriteableBitmapEx）：
private void ResizeNavBarImage(Image src)
{
WriteableBitmap bmpSource = new WriteableBitmap((BitmapSource)src.Source);
int srcWidth = bmpSource.PixelWidth;
int srcHeight = bmpSource.PixelHeight;
int finalDestWidth = 75;
int finalDestHeight = 75;
// Resize
float xFactor = ((float)finalDestWidth / (float)srcWidth);
float yFactor = ((float)finalDestHeight / (float)srcHeight);
float Factor = 0;
if (xFactor < yFactor)
Factor = yFactor;
else
Factor = xFactor;
int destWidth = (int)(srcWidth * Factor);
int destHeight = (int)(srcHeight * Factor);
if (destWidth < destHeight && destWidth != finalDestWidth)
destWidth = finalDestWidth;
else if (destWidth > destHeight && destHeight != finalDestHeight)
destHeight = finalDestHeight;
WriteableBitmap bmpDest = bmpSource.Resize(destWidth, destHeight, WriteableBitmapExtensions.Interpolation.Bilinear);
// Crop
int Offset;
WriteableBitmap bmpFinalDest = new WriteableBitmap(finalDestWidth, finalDestHeight);
if (destWidth > destHeight)
{
Offset = (bmpDest.PixelWidth - bmpDest.PixelHeight) / 2;
if (finalDestWidth % 2 != 0 && Offset % 2 == 0)
Offset -= 1;
bmpFinalDest = bmpDest.Crop(Offset, 0, finalDestWidth, finalDestHeight);
}
else if (destWidth < destHeight)
{
Offset = (bmpDest.PixelHeight - bmpDest.PixelWidth) / 2;
if (finalDestHeight % 2 != 0 && Offset % 2 == 0)
Offset -= 1;
bmpFinalDest = bmpDest.Crop(0, Offset, finalDestWidth, finalDestHeight);
}
else
bmpFinalDest = bmpDest;
src.Source = (ImageSource)bmpFinalDest;
}
i和j的循环将转到srcHeight和srcWidth，而不是destHeight和destWidth。
这可能也不是这段代码中的最后一个错误。
我同意Mark Ransom的观点，调整图像大小的正确方法是使用Graphics对象绘制到另一个图像中。
http://www.switchonthecode.com/tutorials/csharp-tutorial-image-editing-saving-cropping-and-resizing
这将允许您使用不同的、更好的过滤器来获得良好的图像质量，更不用说速度了。
为什么不使用WriteableBitmap的内置缩放功能？
WriteableBitmap wb = new WriteableBitmap(src, new ScaleTransform() { ScaleX = 0.25, ScaleY = 0.25 });
wb.Invalidate();
src.Source = wb;