Method: Magick::Image#ordered_dither

Defined in:
ext/RMagick/rmimage.cpp

#ordered_dither(threshold_map = '2x2') ⇒ Magick::Image

Dithers the image to a predefined pattern. The threshold_map argument defines the pattern to use.

  • Default threshold_map is ‘2x2’

  • Order of threshold_map must be 2, 3, or 4.

Returns a new image.

Parameters:

  • threshold_map (String, Numeric) (defaults to: '2x2') —

    the threshold

Returns:



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# File 'ext/RMagick/rmimage.cpp', line 10341

VALUE
Image_ordered_dither(int argc, VALUE *argv, VALUE self)
{
    Image *image, *new_image;
    int order;
    const char *threshold_map = "2x2";
    ExceptionInfo *exception;

    image = rm_check_destroyed(self);

    if (argc > 1)
    {
        rb_raise(rb_eArgError, "wrong number of arguments (%d for 0 or 1)", argc);
    }
    if (argc == 1)
    {
        if (TYPE(argv[0]) == T_STRING)
        {
            threshold_map = StringValueCStr(argv[0]);
        }
        else
        {
            order = NUM2INT(argv[0]);
            if (order == 3)
            {
                threshold_map = "3x3";
            }
            else if (order == 4)
            {
                threshold_map = "4x4";
            }
            else if (order != 2)
            {
                rb_raise(rb_eArgError, "order must be 2, 3, or 4 (%d given)", order);
            }
        }
    }

    new_image = rm_clone_image(image);

    exception = AcquireExceptionInfo();

#if defined(IMAGEMAGICK_7)
    GVL_STRUCT_TYPE(OrderedDitherImage) args = { new_image, threshold_map, exception };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(OrderedDitherImage), &args);
#else
    GVL_STRUCT_TYPE(OrderedPosterizeImage) args = { new_image, threshold_map, exception };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(OrderedPosterizeImage), &args);
#endif
    rm_check_exception(exception, new_image, DestroyOnError);

    DestroyExceptionInfo(exception);

    return rm_image_new(new_image);
}