Method: Magick::Image#level_channel

Defined in:
ext/RMagick/rmimage.cpp

#level_channel(aChannelType, black = 0.0, white = 1.0, gamma = Magick::QuantumRange) ⇒ Magick::Image

Similar to #level2 but applies to a single channel only.

Returns a new image.

Parameters:

  • aChannelType (Magick::ChannelType) —

    A ChannelType value.

  • black (Numeric) (defaults to: 0.0) —

    A black point level in the range 0..QuantumRange.

  • white (Numeric) (defaults to: 1.0) —

    A white point level in the range 0..QuantumRange.

  • gamma (Numeric) (defaults to: Magick::QuantumRange) —

    A gamma correction in the range 0.0 - 10.0.

Returns:

See Also:



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# File 'ext/RMagick/rmimage.cpp', line 8556

VALUE
Image_level_channel(int argc, VALUE *argv, VALUE self)
{
    Image *image, *new_image;
    double black_point = 0.0, gamma_val = 1.0, white_point = (double)QuantumRange;
    ChannelType channel;
#if defined(IMAGEMAGICK_7)
    ExceptionInfo *exception;
#endif

    image = rm_check_destroyed(self);
    switch (argc)
    {
        case 1:             // take all the defaults
            break;
        case 2:
            black_point = NUM2DBL(argv[1]);
            white_point = QuantumRange - black_point;
            break;
        case 3:
            black_point = NUM2DBL(argv[1]);
            white_point = NUM2DBL(argv[2]);
            break;
        case 4:
            black_point = NUM2DBL(argv[1]);
            white_point = NUM2DBL(argv[2]);
            gamma_val   = NUM2DBL(argv[3]);
            break;
        default:
            rb_raise(rb_eArgError, "wrong number of arguments (%d for 1 to 4)", argc);
            break;
    }

    VALUE_TO_ENUM(argv[0], channel, ChannelType);

    new_image = rm_clone_image(image);

#if defined(IMAGEMAGICK_7)
    exception = AcquireExceptionInfo();
    BEGIN_CHANNEL_MASK(new_image, channel);
    GVL_STRUCT_TYPE(LevelImage) args = { new_image, black_point, white_point, gamma_val, exception };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(LevelImage), &args);
    END_CHANNEL_MASK(new_image);
    rm_check_exception(exception, new_image, DestroyOnError);
    DestroyExceptionInfo(exception);
#else
    GVL_STRUCT_TYPE(LevelImageChannel) args = { new_image, channel, black_point, white_point, gamma_val };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(LevelImageChannel), &args);
    rm_check_image_exception(new_image, DestroyOnError);
#endif

    return rm_image_new(new_image);
}