Method: Magick::Image#sigmoidal_contrast_channel

Defined in:

ext/RMagick/rmimage.cpp

#sigmoidal_contrast_channel(contrast = 3.0, midpoint = 50.0, sharpen = false, channel = Magick::AllChannels) ⇒ Magick::Image #sigmoidal_contrast_channel(contrast = 3.0, midpoint = 50.0, sharpen = false, *channels) ⇒ Magick::Image

Adjusts the contrast of an image channel with a non-linear sigmoidal contrast algorithm. Increases the contrast of the image using a sigmoidal transfer function without saturating highlights or shadows.

Overloads:

• #sigmoidal_contrast_channel(contrast = 3.0, midpoint = 50.0, sharpen = false, channel = Magick::AllChannels) ⇒ Magick::Image

  Parameters:

  • contrast (Numeric) (defaults to: 3.0) —

    indicates how much to increase the contrast (0 is none; 3 is typical; 20 is pushing it)

  • midpoint (Numeric) (defaults to: 50.0) —

    indicates where midtones fall in the resultant image (0 is white; 50% is middle-gray; 100% is black). Note that “50%” means “50% of the quantum range.” This argument is a number between 0 and QuantumRange. To specify “50%” use QuantumRange * 0.50.

  • sharpen (Boolean) (defaults to: false) —

    Set sharpen to true to increase the image contrast otherwise the contrast is reduced.

  • channel (Magick::ChannelType) (defaults to: Magick::AllChannels) —

    a ChannelType arguments.

• #sigmoidal_contrast_channel(contrast = 3.0, midpoint = 50.0, sharpen = false, *channels) ⇒ Magick::Image

  Parameters:

  • contrast (Numeric) (defaults to: 3.0) —

    indicates how much to increase the contrast (0 is none; 3 is typical; 20 is pushing it)

  • midpoint (Numeric) (defaults to: 50.0) —

    indicates where midtones fall in the resultant image (0 is white; 50% is middle-gray; 100% is black). Note that “50%” means “50% of the quantum range.” This argument is a number between 0 and QuantumRange. To specify “50%” use QuantumRange * 0.50.

  • sharpen (Boolean) (defaults to: false) —

    Set sharpen to true to increase the image contrast otherwise the contrast is reduced.

  • *channels (Magick::ChannelType) —

    one or more ChannelType arguments.

Returns:

• (Magick::Image) —

  a new image

# File 'ext/RMagick/rmimage.cpp', line 13198

VALUE
Image_sigmoidal_contrast_channel(int argc, VALUE *argv, VALUE self)
{
    Image *image, *new_image;
    MagickBooleanType sharpen = MagickFalse;
    double contrast = 3.0;
    double midpoint = 50.0;
    ChannelType channels;
#if defined(IMAGEMAGICK_7)
    ExceptionInfo *exception;
#endif

    image = rm_check_destroyed(self);
    channels = extract_channels(&argc, argv);

    switch (argc)
    {
        case 3:
            sharpen  = (MagickBooleanType) RTEST(argv[2]);
        case 2:
            midpoint = NUM2DBL(argv[1]);
        case 1:
            contrast = NUM2DBL(argv[0]);
        case 0:
            break;
        default:
            raise_ChannelType_error(argv[argc-1]);
            break;
    }

    new_image = rm_clone_image(image);

#if defined(IMAGEMAGICK_7)
    exception = AcquireExceptionInfo();
    BEGIN_CHANNEL_MASK(new_image, channels);
    GVL_STRUCT_TYPE(SigmoidalContrastImage) args = { new_image, sharpen, contrast, midpoint, exception };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(SigmoidalContrastImage), &args);
    END_CHANNEL_MASK(new_image);
    rm_check_exception(exception, new_image, DestroyOnError);
    DestroyExceptionInfo(exception);
#else
    GVL_STRUCT_TYPE(SigmoidalContrastImageChannel) args = { new_image, channels, sharpen, contrast, midpoint };
    CALL_FUNC_WITHOUT_GVL(GVL_FUNC(SigmoidalContrastImageChannel), &args);
    rm_check_image_exception(new_image, DestroyOnError);
#endif

    return rm_image_new(new_image);
}