.NET中生成水印更好的方法

C#

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2019-6-30

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.NET中生成水印更好的方法

为了保护知识产权,防止资源被盗用,水印在博客、网店等场景中非常常见。

本文首先演示了基于System.Drawing.Image做正常操作。然后基于Direct2D/WIC/DirectWrite,演示了一种全新、不同的“”操作。

方法1-System.Drawing给图片加水印

System.Drawing.Image原生属于GDI的一部分,是Windows Only,但随着NuGet包System.Drawing.Common的发布,现在System.Drawing.Image已经支持linux

Install-Package System.Drawing.Common -Version 4.5.1

以下代码演示了如何从给图片加水印:

// 加水印
var watermarkedStream = new MemoryStream();
using (var img = Image.FromStream(File.OpenRead(@"D:\_\WatermarkDemo.png")))
{
    using (var graphic = Graphics.FromImage(img))
    {
        var font = new Font("微软雅黑", 30, FontStyle.Bold, GraphicsUnit.Pixel);
        var color = Color.FromArgb(128, 255, 255, 255);
        var brush = new SolidBrush(color);
        var point = new Point(img.Width - 130, img.Height - 50);

        graphic.DrawString("水印在此", font, brush, point);
        img.Save(watermarkedStream, ImageFormat.Png);
    }
}

效果如图(没有黄色剪头):

附:Edi.Wang做了一个NuGet包,可以轻松地配置水印参数:

  • NuGet:https://github.com/EdiWang/Edi.ImageWatermark
  • 文章:https://edi.wang/post/2018/10/12/add-watermark-to-uploaded-image-aspnet-core

方法2-Direct2D/WIC给图片加水印

Direct2D源于Windows 8/IE 10,安装IE 10之后,Windows 7也能用。Direct2D基于Direct3D,很显然,是Windows Only的。

Direct2DWindows下一代的2D渲染库,随着Direct2D一起发布的,还有Windows Imaging Component(简称WIC)和DirectWrite

相关说明和文档链接:

技术 说明 链接
Direct2D 基于硬件加速的2D图形渲染 Go
WIC 高性能图片编码、解码 Go
DirectWrite 基于硬件加速的文字渲染 Go

如果您打开链接看了一眼,就不难看出,这些技术都是基于COM的,但我们使用.NET,不是吗?

好在我们有SharpDX

SharpDX对这些DirectX技术做了封装,在这个Demo中,我们需要安装SharpDX.Direct2D1SharpDX.Mathematics两个包:

Install-Package SharpDX.Direct2D1 -Version 4.2.0
Install-Package SharpDX.Mathematics -Version 4.2.0

以下代码演示了如何使用SharpDX.Direct2D1给图片加水印:

using D2D = SharpDX.Direct2D1;
using DWrite = SharpDX.DirectWrite;
using SharpDX;
using SharpDX.IO;
using WIC = SharpDX.WIC;

MemoryStream AddWatermark(Stream fileName, string watermarkText)
{
    using (var wic = new WIC.ImagingFactory2())
    using (var d2d = new D2D.Factory())
    using (var image = CreateWicImage(wic, fileName))
    using (var wicBitmap = new WIC.Bitmap(wic, image.Size.Width, image.Size.Height, WIC.PixelFormat.Format32bppPBGRA, WIC.BitmapCreateCacheOption.CacheOnDemand))
    using (var target = new D2D.WicRenderTarget(d2d, wicBitmap, new D2D.RenderTargetProperties()))
    using (var bmpPicture = D2D.Bitmap.FromWicBitmap(target, image))
    using (var dwriteFactory = new SharpDX.DirectWrite.Factory())
    using (var brush = new D2D.SolidColorBrush(target, new Color(0xff, 0xff, 0xff, 0x7f)))
    {
        target.BeginDraw();
        {
            target.DrawBitmap(bmpPicture, new RectangleF(0, 0, target.Size.Width, target.Size.Height), 1.0f, D2D.BitmapInterpolationMode.Linear);
            target.DrawRectangle(new RectangleF(0, 0, target.Size.Width, target.Size.Height), brush);
            var textFormat = new DWrite.TextFormat(dwriteFactory, "微软雅黑", DWrite.FontWeight.Bold, DWrite.FontStyle.Normal, 30.0f);
            target.DrawText(watermarkText, textFormat, new RectangleF(target.Size.Width - 130, target.Size.Height - 50, int.MaxValue, int.MaxValue), brush);
        }
        target.EndDraw();

        var ms = new MemoryStream();
        SaveD2DBitmap(wic, wicBitmap, ms);
        return ms;
    }
}

void SaveD2DBitmap(WIC.ImagingFactory wicFactory, WIC.Bitmap wicBitmap, Stream outputStream)
{
    using (var encoder = new WIC.BitmapEncoder(wicFactory, WIC.ContainerFormatGuids.Png))
    {
        encoder.Initialize(outputStream);
        using (var frame = new WIC.BitmapFrameEncode(encoder))
        {
            frame.Initialize();
            frame.SetSize(wicBitmap.Size.Width, wicBitmap.Size.Height);

            var pixelFormat = wicBitmap.PixelFormat;
            frame.SetPixelFormat(ref pixelFormat);
            frame.WriteSource(wicBitmap);

            frame.Commit();
            encoder.Commit();
        }
    }
}

WIC.FormatConverter CreateWicImage(WIC.ImagingFactory wicFactory, Stream stream)
{
    using (var decoder = new WIC.PngBitmapDecoder(wicFactory))
    {
        var decodeStream = new WIC.WICStream(wicFactory, stream);
        decoder.Initialize(decodeStream, WIC.DecodeOptions.CacheOnLoad);
        using (var decodeFrame = decoder.GetFrame(0))
        {
            var converter = new WIC.FormatConverter(wicFactory);
            converter.Initialize(decodeFrame, WIC.PixelFormat.Format32bppPBGRA);
            return converter;
        }
    }
}

调用方式:

File.WriteAllBytes(@"D:\_\Demo2.png", AddWatermark(File.OpenRead(@"D:\_\WatermarkDemo.png"), "水印在此").ToArray());

效果也是一切正常:

有什么区别?

System.Drawing只花了14行,Direct2D却需要整整60行!复杂程度惊人!为什么要舍简单求复杂呢?

因为System.Drawing没有硬件加速,而且生成的图片也没有反走样(Anti-aliasing),这导致使用System.Drawing相比之下较慢,而且生成图片的效果稍差:

很明显可以看出,Direct2D生成的图片更平滑。

作者:周杰
出处:https://www.cnblogs.com/sdflysha
本文采用 知识共享署名-非商业性使用-相同方式共享 2.5 中国大陆许可协议 进行许可,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接。

作者:周杰的代码骚操作