Question

我使用下面的代码生成带水印的图像，问题是，即使生成的文件的尺寸较小，生成的文件也总是比原始文件大，例如：

original.jpg（1920 * 1440）= 1.11 MB

generated.jpg（960 * 720）= 1.77 MB

我错过了什么吗？

C＃：

private void AddWaterMark(string target, string NewName, string newwidth, string newheight)
{
    Image imgToResize = Image.FromFile(Path.Combine(target, NewName));
    Bitmap indexedImage = new Bitmap(imgToResize, newwidth, newheight);
    Graphics g = Graphics.FromImage(indexedImage);
    g.DrawImage(indexedImage, new Rectangle(0, 0, newwidth, newheight), 0, 0, indexedImage.Width, indexedImage.Height, GraphicsUnit.Pixel);

    g.RotateTransform(-35);

    g.DrawString("WWW.example.COM", new Font("Verdana", 24, FontStyle.Bold), new SolidBrush(Color.FromArgb(75, 255, 255, 255)), -100, 350);
    imgToResize.Dispose();
    indexedImage.Save(target + "\\" + NewName);
    indexedImage.Dispose();
    g.Dispose();

}

VB：

Private Sub AddWaterMark(target As String, NewName As String, newwidth As String, newheight As String)

    Dim imgToResize As Image = Image.FromFile(Path.Combine(target, NewName))
    Dim indexedImage As New Bitmap(imgToResize, newwidth, newheight)
    Dim g As Graphics = Graphics.FromImage(indexedImage)
    g.DrawImage(indexedImage, New Rectangle(0, 0, newwidth, newheight), 0, 0, indexedImage.Width, indexedImage.Height, GraphicsUnit.Pixel)

    g.RotateTransform(-35)

    g.DrawString("WWW.example.COM", New Font("Verdana", 24, FontStyle.Bold), New SolidBrush(Color.FromArgb(75, 255, 255, 255)), -100, 350)
    imgToResize.Dispose()
    indexedImage.Save(target + "\" + NewName)
    indexedImage.Dispose()
    g.Dispose()

End Sub

Answer 1

您需要指定质量，例如：

var jpgEncoder = GetEncoder(ImageFormat.Jpeg);
var jpgParameters = new EncoderParameters(1);
jpgParameters.Param[0] = new EncoderParameter(Encoder.Quality, 80L);
indexedImage.Save(target + "\\" + NewName, jpgEncoder, jpgParameters);

并使用此方法：

private ImageCodecInfo GetEncoder(ImageFormat format)
{
    ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

    foreach (ImageCodecInfo codec in codecs)
    {
        if (codec.FormatID == format.Guid)
            return codec;
    }
    return null;
}

Answer 2

JPEG格式具有品质因数。您可以定义生成的图像将被压缩多少。压缩的越多，您丢失的质量就越高。您可以使用Save方法设置质量级别。

看看这里的例子： http://msdn.microsoft.com/en-us/library/ytz20d80%28v=vs.110%29.aspx

可在此处找到不同质量等级的样本：http://en.wikipedia.org/wiki/JPEG#Effects_of_JPEG_compression

为什么生成的水印图像比原始图像大得多？

2 个答案: