image::Decoder fails to detect several format where the individual decoders succeeds in creation

[amyspark]

Hi,

This is to report that in image-extras the following formats fail at ImageReader::into_decoder() but creating individual Decoder instances do succeed:

• WBMP
• PCX
• SGI
• XPM

Like #39 and image-rs/image#2892 the template for validating MIME type I'm using is as follows:

fn type_find(typefind: &mut gst::TypeFind) {
    use gst::{Caps, TypeFindProbability};

    let cursor = std::io::BufReader::new(W::from(&mut *typefind));
    if let Ok(decoder) = image_extras::wbmp::WbmpDecoder::new(cursor) {
        let d = decoder.dimensions();
        gst::log!(
            CAT,
            "extracted WAP bitmap width and height: {}x{}",
            d.0,
            d.1
        );
        typefind.suggest(
            TypeFindProbability::Maximum,
            &Caps::builder("image/vnd.wap.wbmp").build(),
        );
    }
}

Tthe following is the piece of GStreamer code creating the decoder instance, ImageFormat is my own wrapper over image::Format, which will fail casting if the format doesn't have a valid enum:

        let mut reader = ImageReader::new(source);

        let format = state
            .format_from_caps
            .ok_or(gst::FlowError::NotNegotiated)?;

        if let Ok(v) = ImageFormat::try_from(format) {
            reader.set_format(v);
        }

        if settings.max_alloc != 0 {
            let mut limits = Limits::default();
            limits.max_alloc = Some(settings.max_alloc);
            reader.limits(limits);
        }

        drop(settings);

        let mut decoder = reader.into_decoder().map_err(|v| {
            gst::error!(CAT, imp = self, "Failed decoding single image: {v}");
            gst::FlowError::Error
        })?;

All of the formats above return the same error 0:00:00.639300000 18504 21532 ERROR imagersdec video\image\src\decoder\imp.rs:286:gstimagers::decoder::imp::Decoder::render_single_frame::{{closure}}:<imagersdecoder0> Failed decoding single image: The image format could not be determined.

This should not be possible because the typefinding functions have already created a decoder for the supplied files and read basic metadata.

I attach samples for the above formats. All of them were sourced from known working sites, in particular https://resources.oreilly.com/examples/9781565920583/-/tree/master/CDROM/GFF/SAMPLE/IMAGES/SGIIMAGE, https://people.math.sc.edu/Burkardt/data/pcx/pcx.html, and the corresponding entries in Archiveteam e.g. http://justsolve.archiveteam.org/wiki/WBMP.

hose.zip

[mstoeckl]

I don't exactly follow the example code you've given above, but the error "The image format could not be determined" is probably coming from ImageReader::require_format; are you certain that reader.set_format(v); is being called? Without that (or a call to with_guessed_format(), or construction via ImageReader::open) ImageReader will not choose an image type.

Possibly relevant: image-rs/image#2616

[amyspark]

Without that (or a call to with_guessed_format(), or construction via ImageReader::open) ImageReader will not choose an image type.

There's no public API for setting a Format::Extension instance; moreover, the images are always opened on my side from Read + Seek instances (I don't have access to the file name), so I rely on image-rs's signature sniffing hooks for this to work.

Currently I've added typefinding functions that try-construct Readers and if they work, the file is accepted.

[amyspark]

There's no public API for setting a Format::Extension instance

I should add that I rolled my own Format supertype to implement MIME type instancing/conversion, as image-extras formats are not exposed in the API (plus, I've got some older/different MIME to map to the existing formats).