Cross-Platform Support for Saving Images in JPG Format in .NET MAUI

[VishalOmprasad]

I am developing an image-saving feature in a .NET MAUI application and am seeking guidance on ensuring consistent, cross-platform behavior.
The goal is to allow users to save images in the following formats:

• PNG (.png)
• JPEG (.jpeg)
• BMP (.bmp)
• JPG (as an alternative to .jpeg for JPEG-encoded images)

While PNG, JPEG, and BMP are mostly supported across platforms, adding support for .jpg extension has revealed inconsistent behavior across platforms.

Current Implementation Status:

Windows:

• Saving works as expected for .png, .jpeg, .bmp, and .jpg by providing the format as a string.
• When saving JPEG-encoded data, the resulting .jpg and .jpeg files have identical sizes (e.g., both 300 KB). However, unclear whether this behavior is correct.

Android:

• PNG and BMP formats work correctly.
• When saving a JPEG image using Bitmap.CompressFormat.JPEG, Android's MediaStore automatically assigns a .jpg extension based on the image/jpeg MIME type, regardless of whether .jpeg was specified in the filename..
• Reference:
  • Issue in MediaStore - https://codingtechroom.com/question/https-www-yourwebsite-com-fix-android-mediastore-wrong-file-extension.
  • Bitmap.CompressFormat - https://developer.android.com/reference/android/graphics/Bitmap.CompressFormat.
  • Supported image formats - https://developer.android.com/media/platform/supported-formats#image-formats.
  • StackOverflow - https://stackoverflow.com/questions/59182066/wrong-file-extension-and-file-name-after-creating-image-file-with-androids-medi.

iOS/MacCatalyst:

• UIImage.AsJPEG() and UIImage.AsPNG() work reliably for saving files with .jpeg and .png extensions.
• However, saving a JPEG-encoded image with a .jpg extension results in:
  • Unexpected behavior (e.g., file saved with .png extension or not recognized).
  • Only .jpeg and .png extensions seem to work reliably.
• BMP is not supported natively for encoding, so fallback to PNG occurs.

Questions:

1. What is the recommended approach in .NET MAUI to reliably save a JPEG-encoded image with a .jpg extension on all platforms, especially iOS?
2. Is the behavior on iOS a known limitation of UIImage or the underlying OS, where it strictly prefers the .jpeg extension?
3. On Android, is there any way to override MediaStore's default behavior to enforce a user-specified extension, or should we align with the platform's convention and always use .jpg?
4. Should .jpg be treated as an alias for .jpeg within the application's logic, with platform-specific code to handle the final file extension, or is there a more unified approach?
5. Are there any plans in the .NET MAUI roadmap to abstract this file format and extension handling to ensure more consistent cross-platform behavior?

Any insights, workarounds, or roadmap updates would be greatly appreciated. Thanks in advance!

[rokmeglic71]

Talking to CoPilot AI, you could implement your reusable cross‑platform image saver service. Each platform would threat .jpg/.jpeg file extension properly. Learned from CoPilot AI, it's not an MAUI bug, it's an OS specific working you can cover making. I copied your content to CoPilot AI and got reusable cross‑platform image saver service.

[mobilewares]

I just did recent project (just Android/iOS only) where we were pulling images from the Camera and downsizing/compressing them to target max file size and saving out to jpg for submission to backend API.

Not sure if this helps - but this is what I discovered :

• For initially reading in images/decoding them from Camera/Media Storage- it's best to use the MAUI PlatformImage class to read in the file & do an initial jpg MemoryStram encode (via PlatformImage.Save)- this is particularly important for iOS where images from camera etc may be coming in as raw format or something else.

• For final encoding (where our images needed to be processed/used by backend systems) - we then used the Google SkiaSharp libraries to do final jpeg encoding from the initially encoded MemoryStreams created by PlatformImage.Save(). This seemed to be a lot more stable & faster vs using Platform Image - particularly for getting finer control of compression/resizing/cropping and saved images always working.

It sounds weird the file extension for jpeg is making so much difference here - typically the other tooling is primarily looking at the header of the output file - surprised it doesn't work with either extension as both are commonly used. We did use '.jpg' instead of '.jpeg' but I'm not convinced this would cause the issues.