How I get 300 DPI with 648 X 1016 Using SKBitmap

Question

I am trying to PNG image to BMP image via using SKBitmap, the BMP image not set in 300 DPI why? below i mentioned my code, if there is any mistakes please correct my code

using (SKBitmap pngBitmap = SKBitmap.Decode(inputFilePath))

            {

                // Calculate the scaling factor for 300 DPI


                

                // Calculate the scaled dimensions for the BMP bitmap

                int bmpWidth = pngBitmap.Width;

                int bmpHeight = pngBitmap.Height;

                // Create a new SKBitmap with the scaled dimensions

                using (SKBitmap bmp = new SKBitmap(bmpWidth, bmpHeight))

                {

                    // Copy the PNG bitmap to the BMP bitmap

                    pngBitmap.CopyTo(bmp);

                    // Set the DPI for the BMP bitmap

                   float dpiScale = 300f / 96f;

                    // Save the BMP bitmap to a file

                    using (SKImage img = SKImage.FromBitmap(bmp))

                    using (SKData data = img.Encode())

                    using (var stream = System.IO.File.OpenWrite(outputFilePath))

                    {

                        data.SaveTo(stream);

                    }

                }

Answer 1

Hi @Saranya Karthik , Welcome to Microsoft Q&A,

You may consider using the System.Drawing namespace in .NET Framework or .NET Core.

System.Drawing provides a set of classes and methods for processing images that can be used to achieve your target effects.

Here is sample code implemented using System.Drawing to convert a PNG image to a BMP image and set the DPI:

using System.Drawing;
using System.Drawing.Imaging;

string inputFilePath = "input.png";
string outputFilePath = "output.bmp";

using (Bitmap pngBitmap = new Bitmap(inputFilePath))
{
    // Create a new Bitmap with the same dimensions as the original PNG bitmap
    Bitmap bmpBitmap = new Bitmap(pngBitmap.Width, pngBitmap.Height);

    // Copy the PNG bitmap to the BMP bitmap
    using (Graphics graphics = Graphics.FromImage(bmpBitmap))
    {
        graphics.DrawImage(pngBitmap, 0, 0);
    }

    // Set the DPI for the BMP bitmap
    bmpBitmap.SetResolution(300, 300);

    // Save the BMP bitmap to a file
    bmpBitmap.Save(outputFilePath, ImageFormat.Bmp);
}

Best Regards,

Jiale

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Answer 2

Hi @Saranya Karthik ,

System.Drawing.Common is not supported on UWP.

It is recommended that you use WriteableBitmap to read png files and save them as new bmp files.

private async void Button_Click_1(object sender, RoutedEventArgs e)
{
    FileOpenPicker fileOpenPicker = new FileOpenPicker();
    fileOpenPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
    fileOpenPicker.FileTypeFilter.Add(".png");
    fileOpenPicker.ViewMode = PickerViewMode.Thumbnail;
    var inputFile = await fileOpenPicker.PickSingleFileAsync();
    if (inputFile == null)
    {
        // The user cancelled the picking operation
        return;
    }
    using (IRandomAccessStream stream = await inputFile.OpenAsync(FileAccessMode.Read))
    {
        // Create the decoder from the stream
        BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
        // Get the SoftwareBitmap representation of the file
        WriteableBitmap writeableBitmap = new WriteableBitmap((int)decoder.PixelWidth, (int)decoder.PixelHeight);
        await writeableBitmap.SetSourceAsync(stream);
        Windows.Storage.StorageFolder storageFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
        Windows.Storage.StorageFile bmpFile = await storageFolder.CreateFileAsync("bitmap.bmp", Windows.Storage.CreationCollisionOption.ReplaceExisting);
        SaveSoftwareBitmapToFile(writeableBitmap, bmpFile);
    }
}
private async void SaveSoftwareBitmapToFile(WriteableBitmap softwareBitmap, StorageFile outputFile)
{
    using (IRandomAccessStream stream = await outputFile.OpenAsync(FileAccessMode.ReadWrite))
    {
        // Create an encoder with the desired format
        BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, stream);
                
        var pixelStream = softwareBitmap.PixelBuffer.AsStream();
        byte[] pixels = new byte[softwareBitmap.PixelBuffer.Length];
        await pixelStream.ReadAsync(pixels, 0, pixels.Length);
        encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Ignore, (uint)softwareBitmap.PixelWidth, (uint)softwareBitmap.PixelHeight, 300, 300, pixels);           
                
        await encoder.FlushAsync();
                         
    }
}

Thank you.

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