Cannot convert from AVIF to BMP

[SebastianStehle]

Magick.NET version

11.12

Environment (Operating system, version and so on)

Windows, .NET 6

Description

I have an asset library that supports different formats and stores. I have tests for conversion for all formats, and when I run the test for AVIF -> BMP I have the following behaviors:

1. The bmp file is way too big. 6MB instead of 1.3MB or so, for a 600x600 image.
2. When I load the bmp I get the following error: {"length and filesize do not match ' @ error/bmp.c/ReadBMPImage/847"}`

Steps to Reproduce

Checkout: [email protected]:Squidex/assets.git

Run the following test:

[dlemstra]

Could you reduce this to a small code sample that I can use to reproduce your issue? Otherwise I would need to debug your code.

[SebastianStehle]

Here it is: https://github.com/SebastianStehle/magicktest/tree/main/MagickTest

[dlemstra]

The problem here is how the image is written. Because you are using the Async method the image is first written to a byte array in memory and then saved to the file to make it possible to do the IO part asynchronous. When you don't use the async method separate files would be created. This is a bug that has to be fixed in Magick.NET but that won't solve your issue because looking at your code it seems that you are using a stream instead of a file. And when you are using a stream each "file"/frame will be written to that output stream sequentially. This is by design but I don't know if anyone even uses that.

In your situation I would advise you to use MagickFormatInfo.Create(MagickFormat) and then use the IsMultiFrame property to determine what you want to do. You should probably use a MagickImage when IsMultiFrame returns false instead of a MagickImageCollection.

[SebastianStehle]

But it only happens with bmp and in my sample I do not use streams. All other conversions work.

[SebastianStehle]

Okay, my code was probably wrong. I have changed the saving to this: https://github.com/Squidex/assets/blob/master/Squidex.Assets.ImageMagick/ImageMagickThumbnailGenerator.cs#L125

And this works.

It seems that when I load the avif as collection it has 5 images. No idea, why. And therefore all five images are saved to the bmp stream or file.

[dlemstra]

When you load an image with the MagickImageCollection you will get all the layers/frames of the image.

[SebastianStehle]

Yes. I know. But I created the avif by converting from png manually. So I don't see how it can have more than one 1 layer.