Question

只是想跟你检查一件事。我正在使用WriteableBitmap创建一个我作为实时图块的图像。工作正常，但我注意到文本边缘有阴影。使文本看起来有点脏或乱。

看看下面的图片。左侧部分来自使用WriteableBitmap创建的实时磁贴，右侧部分是Windows Phone标准磁贴（Internet Explorer磁贴）。看到区别？

http://img268.imageshack.us/img268/8749/unled2imo.png http://img268.imageshack.us/img268/8749/unled2imo.png

我能做些什么吗？你以前注意到了吗？

编辑：嗯，我想我正在看错了功能。我认为可能是导致这种情况的wbmp.SaveJpeg？我将文本和背景图像放入网格，然后使用wbmp.SaveJpeg保存。这是什么原因？任何解决方法？

string sIsoStorePath = @"\Shared\ShellContent\tile.png";
using (IsolatedStorageFile appStorage =     IsolatedStorageFile.GetUserStoreForApplication())
{
    //ensure directory exists
    String sDirectory = System.IO.Path.GetDirectoryName(sIsoStorePath);
    if (!appStorage.DirectoryExists(sDirectory))
    {
        appStorage.CreateDirectory(sDirectory);
    }

    using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream(sIsoStorePath, System.IO.FileMode.Create, appStorage))
    {
        wbmp.SaveJpeg(stream, 173, 173, 0, 100);
    }
}

Answer 1

WritableBitmap.Pixels的文档指出“Silverlight WriteableBitmap使用的格式是ARGB32（预乘RGB）”。也许那时的实时图块需要非预乘的像素格式。

我在Silverlight中找不到任何API来更改格式，但我认为本文中的方法可能就是您所需要的：

http://nokola.com/blog/post/2010/01/27/The-Most-Important-Silverlight-WriteableBitmap-Gotcha-Does-It-LoseChange-Colors.aspx

编辑：

根据我的测试，似乎问题出在JPEG压缩工件上，因为即使你用.png扩展名命名，SaveJpeg也会以JPEG格式保存文件。

下面的示例代码对MakeNonPremultiplied（bitmap.Pixels）进行了注释调用，该调用显示了如果使用某个库将其保存为可以使用的文件格式，如何调用过滤器将像素格式修改为非预乘透明度并期望非预乘格式。

using System;
using System.IO;
using System.IO.IsolatedStorage;
using System.Linq;
using System.Windows;
using System.Windows.Media.Imaging;
using Microsoft.Phone.Shell;

namespace LiveTilePlayground
{
    public partial class LiveTileGenerator
    {
        /// <summary>
        /// Renders a FrameworkElement (control) to a bitmap
        /// the size of a live tile or a custom sized square.
        /// </summary>
        /// <param name="element">The element.</param>
        /// <param name="size">
        /// The size of the bitmap (in each dimension).
        /// </param>
        /// <returns></returns>
        public static WriteableBitmap RenderBitmap(
            FrameworkElement element,
            double size = 173.0)
        {
            element.Measure(new Size(size, size));
            element.Arrange(new Rect(0, 0, size, size));
            return new WriteableBitmap(element, null);
        }

        /// <summary>
        /// Updates the primary tile with specific title and background image.
        /// </summary>
        /// <param name="title">The title.</param>
        /// <param name="backgroundImage">The background image.</param>
        public static void UpdatePrimaryTile(string title, Uri backgroundImage)
        {
            ShellTile primaryTile = ShellTile.ActiveTiles.First();
            StandardTileData newTileData = new StandardTileData
            { Title = title, BackgroundImage = backgroundImage };
            primaryTile.Update(newTileData);
        }

        /// <summary>
        /// Saves the tile bitmap with a given file name and returns the URI.
        /// </summary>
        /// <param name="bitmap">The bitmap.</param>
        /// <param name="fileName">Name of the file.</param>
        /// <returns></returns>
        public static Uri SaveTileBitmap(
            WriteableBitmap bitmap, string fileName)
        {
            //MakeNonPremultiplied(bitmap.Pixels);

            using (var store = IsolatedStorageFile.GetUserStoreForApplication())
            {
                if (!store.DirectoryExists(@"Shared\ShellContent"))
                {
                    store.CreateDirectory(@"Shared\ShellContent");
                }

                using (
                    var stream = store.OpenFile(
                        @"Shared\ShellContent\" + fileName,
                        FileMode.OpenOrCreate))
                {
                    bitmap.SaveJpeg(stream, 173, 173, 0, 100);
                }
            }

            return new Uri(
                "isostore:/Shared/ShellContent/" + fileName, UriKind.Absolute);
        }

        /// <summary>
        /// Transforms bitmap pixels to a non-alpha premultiplied format.
        /// </summary>
        /// <param name="bitmapPixels">The bitmap pixels.</param>
        public static void MakeNonPremultiplied(int[] bitmapPixels)
        {
            int count = bitmapPixels.Length;

            // Iterate through all pixels and
            // make each semi-transparent pixel non-premultiplied
            for (int i = 0; i < count; i++)
            {
                uint pixel = unchecked((uint)bitmapPixels[i]);

                // Decompose ARGB structure from the uint into separate channels

                // Shift by 3 bytes to get Alpha
                double a = pixel >> 24;

                // If alpha is 255 (solid color) or 0 (completely transparent) -
                // skip this pixel.
                if ((a == 255) || (a == 0))
                {
                    continue;
                }

                // Shift 2 bytes and filter out the Alpha byte to get Red
                double r = (pixel >> 16) & 255;

                // Shift 1 bytes and filter out Alpha and Red bytes to get Green
                double g = (pixel >> 8) & 255;

                // Filter out Alpha, Red and Green bytes to get Blue
                double b = (pixel) & 255;

                // Divide by normalized Alpha to get non-premultiplied values
                double factor = 256 / a;
                uint newR = (uint)Math.Round(r * factor);
                uint newG = (uint)Math.Round(g * factor);
                uint newB = (uint)Math.Round(b * factor);

                // Compose back to ARGB uint
                bitmapPixels[i] =
                    unchecked((int)(
                        (pixel & 0xFF000000) |
                        (newR << 16) |
                        (newG << 8) |
                        newB));
            }
        }
    }
}

Answer 2

我有完全相同的问题，但对我来说简单的答案是检查使用的透明PNG。它被设置为使用16位颜色深度。将PNG更改为8位颜色深度解决了我的问题。

SaveJpeg导致具有透明度的“阴影”瑕疵

2 个答案: