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Exporting Images in .NET Standard
Updated on Apr 27, 2026
.NET Standard specification does not define APIs for getting the image properties. SpreadProcessing needs to have access to GDI+ basic graphics functionality when exporting spreadsheets that contain images. That is why, to allow the library to get the image properties needed for saving the workbook, an implementation inheriting the ImagePropertiesResolverBase abstract class must be set to the ImagePropertiesResolver property of SpreadExtensibilityManager.
The Telerik.Documents.ImageUtils package provides a default implementation of the ImagePropertiesResolver class that could be used when exporting the document.
Example 1: Set the default implementation of the ImagePropertiesResolver class
C#
ImagePropertiesResolverBase imagePropertiesResolver = new ImagePropertiesResolver();
SpreadExtensibilityManager.ImagePropertiesResolver = imagePropertiesResolver;Example 2: Windows Example: Create a custom implementation inheriting the ImagePropertiesResolverBase abstract class
C#
public class ImageInfo : ImagePropertiesResolverBase
{
public override Size GetImageSize(byte[] imageData)
{
Size size = Size.Empty;
try
{
using (SKBitmap decodedBitmap = SKBitmap.Decode(imageData))
{
size = new Size(decodedBitmap.Width, decodedBitmap.Height);
}
}
catch (Exception ex)
{
// Image format not recognized.
throw new NotSupportedException("Unsupported image format.", ex);
}
return size;
}
public override bool TryGetRawImageData(byte[] imageData, out byte[] rawRgbData, out byte[] rawAlpha, out Size size)
{
using (SKBitmap decodedBitmap = SKBitmap.Decode(imageData))
{
size = new Size(decodedBitmap.Width, decodedBitmap.Height);
GetRawDataFromRgbaSource(decodedBitmap, out rawRgbData, out rawAlpha);
return true;
}
}
private static void GetRawDataFromRgbaSource(SKBitmap decodedBitmap, out byte[] data, out byte[] alpha)
{
bool shouldExportAlpha = false;
List<byte> rawRgbData = new List<byte>(decodedBitmap.ByteCount / 4 * 3);
List<byte> rawAlpha = new List<byte>(decodedBitmap.ByteCount / 4);
SKColor[] pixels = decodedBitmap.Pixels;
for (int i = 0; i < pixels.Length; i++)
{
SKColor pixel = pixels[i];
byte r = pixel.Red;
byte g = pixel.Green;
byte b = pixel.Blue;
byte a = pixel.Alpha;
rawRgbData.Add(r);
rawRgbData.Add(g);
rawRgbData.Add(b);
rawAlpha.Add(a);
if (a != 255)
{
shouldExportAlpha = true;
}
}
data = rawRgbData.ToArray();
alpha = rawAlpha.ToArray();
if (!shouldExportAlpha)
{
alpha = null;
}
}
}Example 3: Set the custom implementation inheriting the ImagePropertiesResolverBase abstract class
C#
ImagePropertiesResolverBase imagePropertiesResolver = new ImageInfo();
SpreadExtensibilityManager.ImagePropertiesResolver = imagePropertiesResolver;