Em 19-05-2011 05:12, Sakari Ailus escreveu:
> Sylwester Nawrocki wrote:
>>>> These were mostly fixed point arithmetic numbers in [32-bit numerator/
>>>> 32-bit denominator] form carrying exposure time, shutter speed, aperture,
>>>> brightness, flash, etc. information. The tags could be read from ISP after
>>>> it buffered a frame in its memory and processed it.
>>>> In case of a JPEG image format the tags can be embedded into the main
>>>> image file. But the image processors not always supported that so we used
>>>> to have an ioctl for the purpose of retrieving the metadata in user space.
>>>> In some cases it is desired to read data directly from the driver rather
>>>> than parsing a relatively large buffer.
>>>> It would be good to have a uniform interface for passing such data to
>>>> applications. I think in that particular use case a control id/value pair
>>>> sequences would do.
> - Which formats are your rational numbers in? A kernel interface can't
> really have floating point numbers, so there would need to be a sane way
> to pass these to user space.
The V4L2 API has support for rational numbers. The frame rate is specified as a
rational number. There's a struct for that:
struct v4l2_fract {
__u32 numerator;
__u32 denominator;
};
Cheers,
Mauro
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