win10 uwp modify picture quality compress picture

本文告诉大家如何在 UWP Reduce image size by modifying the quality of the image,This method only supports output jpg 文件

通过创建 BitmapEncoder 的时候指定 BitmapPropertySet You can set the quality of the picture,只有对 JPG format to set the picture quality

The value of picture quality is from 0 到 1 其中 1 Indicates the best quality

    var propertySet = new BitmapPropertySet();
    // 图片质量,值范围是 0到1 其中 1 的质量最好
    var qualityValue = new BitmapTypedValue(imageQuality,
        Windows.Foundation.PropertyType.Single);
    propertySet.Add("ImageQuality", qualityValue);
    var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, imageWriteAbleStream,
        propertySet);

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这里的 imageQuality It's the picture quality,This needs to be passed in

The method of compressing the image size from an image file can be written like this,Create a method to pass in the original image file,and the file that needs to be output,and picture quality

        private async Task<StorageFile> ConvertImageToJpegAsync(StorageFile sourceFile, StorageFile outputFile,
            double imageQuality)

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Get the image size first,This will give you an idea of ​​how much compressed,Compare the file size of the original image and the compressed image size

            var sourceFileProperties = await sourceFile.GetBasicPropertiesAsync();
            var fileSize = sourceFileProperties.Size;

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An easier way to get the file size is via WinRTXamlToolkit 的 StorageItemExtensions.GetSizeAsync 拿到文件大小

Read the original image file,The original image needs to be decoded first,Then modify the picture quality by encoding

            var imageStream = await sourceFile.OpenReadAsync();

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The decoding method does not need to know the format of the picture

                var decoder = await BitmapDecoder.CreateAsync(imageStream);
                var pixelData = await decoder.GetPixelDataAsync();
                var detachedPixelData = pixelData.DetachPixelData();

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打开输出文件,进行编码

                var imageWriteAbleStream = await outputFile.OpenAsync(FileAccessMode.ReadWrite);

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Set the image quality when creating the codec

    var propertySet = new BitmapPropertySet();
    // 图片质量,值范围是 0到1 其中 1 的质量最好
    var qualityValue = new BitmapTypedValue(imageQuality,
        Windows.Foundation.PropertyType.Single);
    propertySet.Add("ImageQuality", qualityValue);
    var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, imageWriteAbleStream,
        propertySet);

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Write the encoding to a file

    encoder.SetPixelData(decoder.BitmapPixelFormat, decoder.BitmapAlphaMode, decoder.OrientedPixelWidth,
        decoder.OrientedPixelHeight, decoder.DpiX, decoder.DpiY, detachedPixelData);
    await encoder.FlushAsync();
    await imageWriteAbleStream.FlushAsync();

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Get the size of the compressed file only,对比一下

    var jpegImageSize = imageWriteAbleStream.Size;
    // 欢迎访问我博客 https://blog.lindexi.com/ 里面有大量 UWP WPF 博客
    Debug.WriteLine($"The compressed file is smaller than the uncompressed file{fileSize - jpegImageSize}");

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The code for this method of compressing images looks a lot though,But it still seems very simple to open the original image file to decrypt the original image and then output to a new file

        /// <summary>
        /// Convert the original picture to picture quality and compression quality
        /// </summary>
        /// <param name="sourceFile">原来的图片</param>
        /// <param name="outputFile">输出的文件</param>
        /// <param name="imageQuality">图片质量,取值范围是 0 到 1 其中 1 的质量最好,This value is only set correctly jpg 图片有效</param>
        /// <returns></returns>
        private async Task<StorageFile> ConvertImageToJpegAsync(StorageFile sourceFile, StorageFile outputFile,
            double imageQuality)
        {
            var sourceFileProperties = await sourceFile.GetBasicPropertiesAsync();
            var fileSize = sourceFileProperties.Size;
            var imageStream = await sourceFile.OpenReadAsync();
            using (imageStream)
            {
                var decoder = await BitmapDecoder.CreateAsync(imageStream);
                var pixelData = await decoder.GetPixelDataAsync();
                var detachedPixelData = pixelData.DetachPixelData();
                var imageWriteAbleStream = await outputFile.OpenAsync(FileAccessMode.ReadWrite);
                using (imageWriteAbleStream)
                {
                    var propertySet = new BitmapPropertySet();
                    // 图片质量,值范围是 0到1 其中 1 的质量最好
                    var qualityValue = new BitmapTypedValue(imageQuality,
                        Windows.Foundation.PropertyType.Single);
                    propertySet.Add("ImageQuality", qualityValue);
                    var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, imageWriteAbleStream,
                        propertySet);
                    //key thing here is to use decoder.OrientedPixelWidth and decoder.OrientedPixelHeight otherwise you will get garbled image on devices on some photos with orientation in metadata
                    encoder.SetPixelData(decoder.BitmapPixelFormat, decoder.BitmapAlphaMode, decoder.OrientedPixelWidth,
                        decoder.OrientedPixelHeight, decoder.DpiX, decoder.DpiY, detachedPixelData);
                    await encoder.FlushAsync();
                    await imageWriteAbleStream.FlushAsync();
                    var jpegImageSize = imageWriteAbleStream.Size;
                    // 欢迎访问我博客 https://blog.lindexi.com/ 里面有大量 UWP WPF 博客
                    Debug.WriteLine($"The compressed file is smaller than the uncompressed file{fileSize - jpegImageSize}");
                }
            }

            return outputFile;
        }

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So write a test program below

Create a button in the interface

        <Button Content="压缩图片" HorizontalAlignment="Center" VerticalAlignment="Center" Click="Button_OnClick" />

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Get a file at the button,Then create the output file in your own temporary folder,If you really need to use this program to compress pictures then please let the user choose another file

        private async void Button_OnClick(object sender, RoutedEventArgs e)
        {
            var pick = new FileOpenPicker();
            pick.FileTypeFilter.Add(".jpg");
            var file = await pick.PickSingleFileAsync();

            if (file != null)
            {
                await ConvertImageToJpegAsync(file,
                    await ApplicationData.Current.TemporaryFolder.CreateFileAsync("lindexi"),
                    0.75);
            }
        }

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现在尝试运行代码,Click the interface button,You can see the selection by clicking the button

代码放在 github

This code is referencedAlex Sorokoletov的代码

How to convert image to JPEG and specify quality parameter in UWP C# XAML

BitmapEncoder options reference - Windows UWP applications

Create, edit, and save bitmap images - Windows UWP applications