5
这是功能性代码，可将图像缩小至指定的较小尺寸。但它也有几件事情是不擅长：将jpeg图像调整为指定大小
- 它的速度慢
- 可以得到缩放后的图像每次必须确定它有整个图像加载到大小时
- 前做几次迭代一个memoryStream
我想改进它。有没有办法得到一个更好的初步估计，以排除如此多的迭代？我是否全部错了？我创建它的原因是接受任何未知尺寸的图像并将其缩放到一定的尺寸。这将允许更好地规划存储需求。当您缩放到某个高度/宽度时，图像尺寸可能会因我们的需要而变化太多。
您将需要System.Drawing的引用。
//Scale down the image till it fits the given file size.
public static Image ScaleDownToKb(Image img, long targetKilobytes, long quality)
{
//DateTime start = DateTime.Now;
//DateTime end;
float h, w;
float halfFactor = 100; // halves itself each iteration
float testPerc = 100;
var direction = -1;
long lastSize = 0;
var iteration = 0;
var origH = img.Height;
var origW = img.Width;
// if already below target, just return the image
var size = GetImageFileSizeBytes(img, 250000, quality);
if (size < targetKilobytes * 1024)
{
//end = DateTime.Now;
//Console.WriteLine("================ DONE. ITERATIONS: " + iteration + " " + end.Subtract(start));
return img;
}
while (true)
{
iteration++;
halfFactor /= 2;
testPerc += halfFactor * direction;
h = origH * testPerc/100;
w = origW * testPerc/100;
var test = ScaleImage(img, (int)w, (int)h);
size = GetImageFileSizeBytes(test, 50000, quality);
var byteTarg = targetKilobytes * 1024;
//Console.WriteLine(iteration + ": " + halfFactor + "% (" + testPerc + ") " + size + " " + byteTarg);
if ((Math.Abs(byteTarg - size)/(double)byteTarg) < .1 || size == lastSize || iteration > 15 /* safety measure */)
{
//end = DateTime.Now;
//Console.WriteLine("================ DONE. ITERATIONS: " + iteration + " " + end.Subtract(start));
return test;
}
if (size > targetKilobytes * 1024)
{
direction = -1;
}
else
{
direction = 1;
}
lastSize = size;
}
}
public static long GetImageFileSizeBytes(Image image, int estimatedSize, long quality)
{
long jpegByteSize;
using (var ms = new MemoryStream(estimatedSize))
{
SaveJpeg(image, ms, quality);
jpegByteSize = ms.Length;
}
return jpegByteSize;
}
public static void SaveJpeg(Image image, MemoryStream ms, long quality)
{
((Bitmap)image).Save(ms, FindEncoder(ImageFormat.Jpeg), GetEncoderParams(quality));
}
public static void SaveJpeg(Image image, string filename, long quality)
{
((Bitmap)image).Save(filename, FindEncoder(ImageFormat.Jpeg), GetEncoderParams(quality));
}
public static ImageCodecInfo FindEncoder(ImageFormat format)
{
if (format == null)
throw new ArgumentNullException("format");
foreach (ImageCodecInfo codec in ImageCodecInfo.GetImageEncoders())
{
if (codec.FormatID.Equals(format.Guid))
{
return codec;
}
}
return null;
}
public static EncoderParameters GetEncoderParams(long quality)
{
System.Drawing.Imaging.Encoder encoder = System.Drawing.Imaging.Encoder.Quality;
//Encoder encoder = new Encoder(ImageFormat.Jpeg.Guid);
EncoderParameters eparams = new EncoderParameters(1);
EncoderParameter eparam = new EncoderParameter(encoder, quality);
eparams.Param[0] = eparam;
return eparams;
}
//Scale an image to a given width and height.
public static Image ScaleImage(Image img, int outW, int outH)
{
Bitmap outImg = new Bitmap(outW, outH, img.PixelFormat);
outImg.SetResolution(img.HorizontalResolution, img.VerticalResolution);
Graphics graphics = Graphics.FromImage(outImg);
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.DrawImage(img, new Rectangle(0, 0, outW, outH), new Rectangle(0, 0, img.Width, img.Height), GraphicsUnit.Pixel);
graphics.Dispose();
return outImg;
}
调用这将创建一个第二图象是接近大小要求值：
var image = Image.FromFile(@"C:\Temp\test.jpg");
var scaled = ScaleDownToKb(image, 250, 80);
SaveJpeg(scaled, @"C:\Temp\test_REDUCED.jpg", 80);
对于这个具体的例子：
- 原始文件大小：628 KB
- 请求文件大小：250 kB
- 缩放后的文件大小：238 kB
我做了类似的建议什么的。这样的工作，但后来有次在那里，例如，目标规模为250 KB和缩放图像为440 KB（原稿尺寸628 KB）因为有图像或什么的更多细节。这太错误了。感谢您的建议。 – jbobbins