Method: Magick::Image#ordered_dither

Defined in:
ext/RMagick/rmimage.c

#ordered_dither(*args) ⇒ Object

Perform ordered dither on image.

Ruby usage:

- @verbatim Image#ordered_dither @endverbatim
- @verbatim Image#ordered_dither(threshold_map) @endverbatim

Notes:

- Default threshold_map is '2x2'
- Order of threshold_map must be 2, 3, or 4.
- If using ImageMagick >= 6.3.0, order can be any of the threshold strings
  listed by "convert -list Thresholds"
- Does not call OrderedDitherImages anymore. Sometime after ImageMagick
  6.0.0 it quit working. Uses the same routines as ImageMagick and
  GraphicsMagick for their "ordered-dither" option.

Parameters:

  • argc —

    number of input arguments

  • argv —

    array of input arguments

  • self —

    this object

Returns:

  • a new image

[View source]

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# File 'ext/RMagick/rmimage.c', line 9509

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 = StringValuePtr(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);

    GetExceptionInfo(&exception);

    // ImageMagick >= 6.2.9
    (void) OrderedPosterizeImage(new_image, threshold_map, &exception);
    rm_check_exception(&exception, new_image, DestroyOnError);

    (void) DestroyExceptionInfo(&exception);

    return rm_image_new(new_image);
}