如何在 UWP C# 中設置圖片和 PDF 大小

Question

我正在嘗試在我的項目中生成一個 pdf，我將圖像轉換為 Pdf 並從布局生成圖像。 生成的圖像尺寸非常大，而且沒有收到好的質量。 請幫我解決這個問題。

我在程序中使用此代碼。

 RenderTargetBitmap renderTargetBitmapimg = new RenderTargetBitmap();

            var mainlayoutHeight = pageStackPanel.ActualHeight;
            var mainlayoutWidth = pageStackPanel.ActualWidth;
            int mlHeight = Convert.ToInt32(mainlayoutHeight);
            int mlWidth = Convert.ToInt32(mainlayoutWidth);


            
            await renderTargetBitmapimg.RenderAsync(pageStackPanel, mlWidth, mlHeight);
            
            ///SAVE IMAGE IN FOLDER 
            var pixelBufferimg = await renderTargetBitmapimg.GetPixelsAsync();
            var pixels = pixelBufferimg.ToArray();
            var displayInformation = DisplayInformation.GetForCurrentView();
            var storageFolder = await KnownFolders.GetFolderForUserAsync(null, KnownFolderId.PicturesLibrary);

            StorageFolder projectFolder = await storageFolder.CreateFolderAsync("TestImage", CreationCollisionOption.OpenIfExists);
            var file = await projectFolder.CreateFileAsync(jpgFilename, CreationCollisionOption.GenerateUniqueName);

            using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
            {
                var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, stream);
                encoder.SetPixelData(BitmapPixelFormat.Bgra8,
                                     BitmapAlphaMode.Premultiplied,
                                    (uint)renderTargetBitmapimg.PixelWidth,
                                    (uint)renderTargetBitmapimg.PixelHeight,
                                    200, 200,
                                    pixels);

                await encoder.FlushAsync();
                StorageFile prescriptionJpgFile = await projectFolder.GetFileAsync(jpgFilename);
                await stream.FlushAsync();
                stream.Seek(0);
                stream.Dispose();
                renderTargetBitmapimg = null;

Answer 1

答案是否定的，不能設置生成的圖片文件的大小。 但是您可以嘗試通過指定特定的寬度和高度來調整它的大小以減小其物理尺寸。 您可以使用 BitmapEncoder class 對原始圖像進行編碼，更改圖像的BitmapInterpolationMode 。 代碼如下所示：

    //open file as stream
        using (IRandomAccessStream fileStream = await imagefile.OpenAsync(FileAccessMode.ReadWrite))
        {
            var decoder = await BitmapDecoder.CreateAsync(fileStream);

            var resizedStream = new InMemoryRandomAccessStream();

            BitmapEncoder encoder = await BitmapEncoder.CreateForTranscodingAsync(resizedStream, decoder);
            double widthRatio = (double)reqWidth / decoder.PixelWidth;
            double heightRatio = (double)reqHeight / decoder.PixelHeight;

            double scaleRatio = Math.Min(widthRatio, heightRatio);

            if (reqWidth == 0)
                scaleRatio = heightRatio;

            if (reqHeight == 0)
                scaleRatio = widthRatio;

            uint aspectHeight = (uint)Math.Floor(decoder.PixelHeight * scaleRatio);
            uint aspectWidth = (uint)Math.Floor(decoder.PixelWidth * scaleRatio);

            encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Linear;

            encoder.BitmapTransform.ScaledHeight = aspectHeight;
            encoder.BitmapTransform.ScaledWidth = aspectWidth;

            await encoder.FlushAsync();
            resizedStream.Seek(0);
            var outBuffer = new byte[resizedStream.Size];
            await resizedStream.ReadAsync(outBuffer.AsBuffer(), (uint)resizedStream.Size, InputStreamOptions.None);


            StorageFolder storageFolder = ApplicationData.Current.LocalFolder;
            Debug.WriteLine(storageFolder.Path);
            StorageFile sampleFile = await storageFolder.CreateFileAsync("testfile.pdf", CreationCollisionOption.ReplaceExisting);
            await FileIO.WriteBytesAsync(sampleFile, outBuffer);

        }

有關更多信息，您可以查看此文檔： How to Compress image and change its Size 。

另一個建議是您可以只使用 UWP 打印 API 來生成 PDF 文件。 你可以看看 Windows Community Toolkit 的Print Helper 。 您可以選擇不打印，而是將其另存為 PDF 文件。