Re: [Boost-users] [gil] Using gil::color_converted_view with gil::for_each_pixel

Hi Chris, please see below: On Sat, Dec 4, 2010 at 1:00 PM, Chris Yuen wrote:

Hey guys,

I realized that writing to gil::color_converted_view doesn't affect the underlying view's data. I wonder if that's correct?

Yes, you're correct about your findings. The color of a pixel is only converted when you access that pixel. That's the mantra of all mutating views. Which can save a lot operations if you don't need the whole image to be converted.

For example, let's say that I want to write a program that will take the value of the red channel and set the blue channel's value to half of that. Here's my failed attempt:

template <typename SrcView> void half_red_to_blue(SrcView & view) {     // Since SrcView might be RGB or BGR or some other types,     // I decided to use a color_converted_view to ensure that I'm     // accessing the correct channels

Are you aware of "get_color()"? Here is small example: rgb8_image_t img( 10, 10 ); rgb8_pixel_t p = *view( img ).xy_at( 0, 0 ); unsigned char c = get_color( p, red_t() ); This works for rgb, bgr, etc.

    type gil::color_converted_view_type::type MyView;     MyView my_view = gil::color_converted_viewgil::rgb8_pixel_t(view):

    struct my_lambda     {         void operator()(gil::rgb8_pixel_t & p)         {             p[2] = p[0] / 2;         }     };

    gil::for_each_pixel(my_view, my_lambda()); }

Does that answer you question? Please mail back if you have more questions. A complete source code example would be very helpful to address your needs. Regards, Christian PS: There is a review of my io extension for gil going on right now. If you have some time please write a review. Thanks!