Lubomir: I appreciate the fast response, your suggestion worked like a charm, so I'll take the example a step further - suppose that I actually want to convert floating-point RGBA data to 8bpp integer RGB (I'm going to display the alpha separately, say). The current default policy for conversion from RGBA to RGB is to multiply the RGB channels by the alpha channel, which is inappropriate in this case - I just want to extract RGB and ignore the alpha. I can override the default by creating my own specialization: namespace gil { template <typename T1, typename T2> struct color_converter_default_impl<T1,rgba_t,T2,rgb_t> { template <typename P1, typename P2> void operator()(const P1& src, P2& dst) const { dst.red = channel_convert<T2>(src.red); dst.green = channel_convert<T2>(src.green); dst.blue = channel_convert<T2>(src.blue); } }; } // namespace gil ... but this is a fairly intrusive, blanket replacement of the default. How would you handle this on a case-by-case basis? I'd liken it to providing custom functors for an STL algorithm. Regards, Tim Shead On Mon, 2006-10-16 at 22:21 -0700, Lubomir Bourdev wrote:
Hi Tim,
We don't recommend that you treat half as compatible with bits8.
In general, GIL does not allow standard copying using copy_pixels, operator=, etc. between pixels that are incompatible. For pixels to be compatible they must have the same base color space and channel types. (See PixelsCompatibleConcept) In other words, you must be able to convert back and forth between them with no loss of precision.
In your case you want to perform a lossy conversion between half and bits8. You have to do it via color conversion, which is allowed to be lossy. To do that you must make half model ChannelConvertibleConcept. Here is how to do what you want:
namespace gil { template <> inline bits8 _channel_convert<bits8>(half h) { return bits8(h*255); } }
boost::function_requires<ChannelConvertibleConcept<half,bits32f> >(); rgb16f_image_t a(100, 100); rgb8_image_t b(100, 100); copy_and_convert_pixels(const_view(a), view(b));
Lubomir
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Timothy M. Shead Sent: Monday, October 16, 2006 8:14 PM To: boost@lists.boost.org Subject: [boost] Generic Image Library (GIL) and floating-point types
I am trying to use GIL with the OpenEXR library, which uses half-precision floating-point channels:
typedef image_type<half, rgb_t>::type rgb16f_image_t; typedef pixel<half, rgb_t> rgb16f_pixel_t;
... which works fine. However, I also need to convert to 8bpp integer images for use with a UI toolkit:
rgb16f_image_t a(100, 100); rgb8_image_t b(100, 100); copy_pixels(const_view(a), view(b));
After providing a specialization for PixelsCompatibleConcept the code compiles fine, but I would like to provide my own code for converting channels of type "half" to type "bits8" (e.g: to convert values in the range [0, 1] to [0, 255]).
Any thoughts?
Tim Shead
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