原文:如何用MediaCapture解决二维码扫描问题(有修改)
二维码扫描的实现,简单的来说可以分三步走:“成像”、“截图”与“识别”。
UWP开发中,最常用的媒体工具非MediaCapture莫属了,下面就来简单介绍一下如何利用MediaCapture来实现扫描和截图并且利用Zxing识别二维码,以及会遇到的问题和需要注意的地方。
1. 初始化与成像
private async void InitMediaCaptureAsync() { //选择后置摄像头 var cameraDevice = await FindCameraDeviceByPanelAsync(Windows.Devices.Enumeration.Panel.Back); if (cameraDevice == null) { System.Diagnostics.Debug.WriteLine("No camera device found!"); return; } var settings = new MediaCaptureInitializationSettings { StreamingCaptureMode = StreamingCaptureMode.Video, //MediaCategory = MediaCategory.Other, //AudioProcessing = AudioProcessing.Default, PhotoCaptureSource = PhotoCaptureSource.VideoPreview, AudioDeviceId = string.Empty, VideoDeviceId = cameraDevice.Id }; await _mediaCapture.InitializeAsync(settings); //摄像头旋转90度 //_mediaCapture.SetPreviewRotation(VideoRotation.Clockwise90Degrees); var fff = _mediaCapture.MediaCaptureSettings; capturePreview.Source = _mediaCapture; await _mediaCapture.StartPreviewAsync(); var focusControl = _mediaCapture.VideoDeviceController.FocusControl; if (focusControl.Supported) { var focusSettings = new FocusSettings() { Mode = focusControl.SupportedFocusModes.FirstOrDefault(f => f == FocusMode.Continuous), DisableDriverFallback = true, AutoFocusRange = focusControl.SupportedFocusRanges.FirstOrDefault(f => f == AutoFocusRange.FullRange), Distance = focusControl.SupportedFocusDistances.FirstOrDefault(f => f == ManualFocusDistance.Nearest) }; //设置聚焦,最好使用FocusMode.Continuous,否则影响截图会很模糊,不利于识别 focusControl.Configure(focusSettings); } if (focusControl.Supported) { //开始聚焦 await focusControl.FocusAsync(); } if (_mediaCapture.VideoDeviceController.FlashControl.Supported) { //关闭闪光灯 _mediaCapture.VideoDeviceController.FlashControl.Enabled = false; } }
private static async Task<DeviceInformation> FindCameraDeviceByPanelAsync(Windows.Devices.Enumeration.Panel desired) { var allVideoDevices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture); DeviceInformation desiredDevice = allVideoDevices.FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == desired); return desiredDevice ?? allVideoDevices.FirstOrDefault(); }
2. 截图与识别
private void InitTimer() { _timer = new DispatcherTimer(); //每50毫秒截一次图 _timer.Interval = TimeSpan.FromMilliseconds(50); _timer.Tick += _timer_Tick; _timer.Start(); }
private async void _timer_Tick(object sender, object e) { using (var stream = new InMemoryRandomAccessStream()) { var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; //将截图写入内存流中 await _mediaCapture.CapturePhotoToStreamAsync(ImageEncodingProperties.CreateJpeg(), stream); //利用Zxing识别,成功:停止timer;失败:继续 var reader = new BarcodeReader(); var bitmapWriteable = new WriteableBitmap((int)previewProperties.Width, (int)previewProperties.Height); bitmapWriteable.SetSource(stream.CloneStream()); //bitmapWriteable.SetSource(stream);有问题 var result = reader.Decode(bitmapWriteable); if (!string.IsNullOrEmpty(result.Text)) { _timer.Stop(); } } }
这里顺便说一下如何安装Zxing,打开nuget管理器 命令窗口输入 Install-Package ZXing.Net ,回车; 关于Zxing如何使用,到网上搜索一下有很多教程,这里不再赘述
3. 问题与优化
A) 截图有响声
使用CapturePhotoToStreamAsync来截取图片有的时候会有“咔擦咔擦”声,很影响用户体验,最理想的做法是找到一种能从视频流中直接截取图片的方法,在这里不得不说一句MediaCapture真的真的很强大,MediaCapture给我们提供了直接从视频流中取出其中一帧的方法GetPreviewFrameAsync,于是我把代码进行了如下修改,即流畅又没有烦人的“咔擦咔擦”声
async void _timer_Tick(object sender, object e) { var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; using (var videoFrame = new VideoFrame(BitmapPixelFormat.Rgba8, (int) previewProperties.Width, (int) previewProperties.Height)) { using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame)) { using (var previewFrame = currentFrame.SoftwareBitmap) { WriteableBitmap bitmap = new WriteableBitmap(previewFrame.PixelWidth, previewFrame.PixelHeight); previewFrame.CopyToBuffer(bitmap.PixelBuffer); var buffer = new Windows.Storage.Streams.Buffer((uint)(4 * previewFrame.PixelWidth * previewFrame.PixelHeight)); previewFrame.CopyToBuffer(buffer); //利用Zxing识别,成功:停止timer;失败:继续 var reader = new BarcodeReader(); var result = reader.Decode(bitmap.PixelBuffer.ToArray(), bitmap.PixelWidth, bitmap.PixelHeight, RGBLuminanceSource.BitmapFormat.Unknown); //var result = reader.Decode(bitmapWriteable); if (!string.IsNullOrEmpty(result.Text)) { _timer.Stop(); } } } } }
顺便提一下记得要使用如下两个命名空间
using System.IO; using System.Runtime.InteropServices.WindowsRuntime;
否则无法实现buffer.AsStream().AsRandomAccessStream()
B) 连续聚焦
并不是所有机型都支持连续聚焦的(FocusMode.Continuous),这个时候只能自己实现间断性持续聚焦了
C) 截图之后图片处理
有的时候为了实现一些功能(比如说扫描框)或者提高识别率,我们需要对截取出来的图片进行一些二次处理,或剪裁或缩放或旋转,我们可以使用BitmapDecoder和BitmapEncoder来实现
var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties; using (var videoFrame = new VideoFrame(BitmapPixelFormat.Rgba8, (int)previewProperties.Width, (int)previewProperties.Height)) { using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame)) { using (var previewFrame = currentFrame.SoftwareBitmap) { WriteableBitmap bitmap = new WriteableBitmap(previewFrame.PixelWidth, previewFrame.PixelHeight); previewFrame.CopyToBuffer(bitmap.PixelBuffer); var buffer = new Windows.Storage.Streams.Buffer((uint)(4 * previewFrame.PixelWidth * previewFrame.PixelHeight)); previewFrame.CopyToBuffer(buffer); imageShowPicture.Source = bitmap;//show the picture //利用Zxing识别,成功:停止timer;失败:继续 var reader = new BarcodeReader(); var result = reader.Decode(bitmap.PixelBuffer.ToArray(), bitmap.PixelWidth, bitmap.PixelHeight, RGBLuminanceSource.BitmapFormat.Unknown); using (var stream = buffer.AsStream() .AsRandomAccessStream()) { //var decoder = await BitmapDecoder.CreateAsync(stream); var destStream = new InMemoryRandomAccessStream(); BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, destStream); //var encoder = await BitmapEncoder.CreateForTranscodingAsync(destStream, decoder); encoder.SetSoftwareBitmap(previewFrame); //剪裁 encoder.BitmapTransform.Bounds = new BitmapBounds() { X = 0, Y = 0, Width = 100, Height = 100 }; //缩放 encoder.BitmapTransform.ScaledWidth = 100; encoder.BitmapTransform.ScaledHeight = 100; //旋转 encoder.BitmapTransform.Rotation = BitmapRotation.Clockwise90Degrees; await encoder.FlushAsync(); await destStream.FlushAsync(); var bitmapImage = new BitmapImage(); bitmapImage.SetSource(destStream); imageShowPicture.Source = bitmapImage;//show the picture } } } } if (!string.IsNullOrEmpty(result.Text)) { _timer.Stop(); }
D) 挂起和唤醒
另外值得注意的是,程序在Suspending和Resuming还有Activated时出现的一系列状态转换,这时候很容易引起bug,需要处理好避免crash。
4. 最后
识别出来的字符串处理一般也就超链接和普通文本两种,当然也可以增加条码扫描功能,识别出的是编码,不管怎样,大家可以根据项目具体需求做相应的处理。