Method: Magick::Image#difference

Defined in:

ext/RMagick/rmimage.cpp

#difference(other) ⇒ Array<Float>

Compares two images and computes statistics about their difference.

Parameters:

• other (Magick::Image, Magick::ImageList) —

  Either an imagelist or an image. If an imagelist, uses the current image.

Returns:

• (Array<Float>) —

  An array of three Float values:

  • mean error per pixel

    • The mean error for any single pixel in the image.

  • normalized mean error

    • The normalized mean quantization error for any single pixel in the image. This distance measure is normalized to a range between 0 and 1. It is independent of the range of red, green, and blue values in the image.

  • normalized maximum error

    • The normalized maximum quantization error for any single pixel in the image. This distance measure is normalized to a range between 0 and 1. It is independent of the range of red, green, and blue values in your image.

# File 'ext/RMagick/rmimage.cpp', line 5539

VALUE
Image_difference(VALUE self, VALUE other)
{
    Image *image;
    Image *image2;
    VALUE mean, nmean, nmax;
#if defined(IMAGEMAGICK_7)
    double distortion;
    ExceptionInfo *exception;
#endif

    image = rm_check_destroyed(self);
    other = rm_cur_image(other);
    image2 = rm_check_destroyed(other);

#if defined(IMAGEMAGICK_7)
    exception = AcquireExceptionInfo();
    GVL_STRUCT_TYPE(GetImageDistortion) args = { image, image2, MeanErrorPerPixelErrorMetric, &distortion, exception };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(GetImageDistortion), &args);
    CHECK_EXCEPTION();
    DestroyExceptionInfo(exception);
#else
    GVL_STRUCT_TYPE(IsImagesEqual) args = { image, image2 };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(IsImagesEqual), &args);
    rm_check_image_exception(image, RetainOnError);
#endif

    mean  = rb_float_new(image->error.mean_error_per_pixel);
    nmean = rb_float_new(image->error.normalized_mean_error);
    nmax  = rb_float_new(image->error.normalized_maximum_error);

    RB_GC_GUARD(mean);
    RB_GC_GUARD(nmean);
    RB_GC_GUARD(nmax);

    return rb_ary_new3(3, mean, nmean, nmax);
}