RMagick: class Image (instance methods, part 2)

###### RMagick User's Guide and Reference

# class Image < Object (class and instance methods, part 2)
mixes in Comparable

## instance methods

### enhance

image.enhance -> anImage

#### Description

Applies a digital filter that improves the quality of a noisy image.

#### Returns

A new image

#### Example

The left-hand side has had noise added by `add_noise`. The right-hand side is the result after using `enhance`.

#### See also

median_filter, reduce_noise, unsharp_mask

#### Magick API

EnhanceImage

### equalize

image.equalize -> anImage

#### Description

Applies a histogram equalization to the image.

#### Returns

A new image

#### Example

#### Magick API

EqualizeImage

### erase!

image.erase! -> image

#### Description

Sets the entire image to the background color.

#### Returns

self

#### See also

color_reset!

#### Magick API

SetImage

### export_pixels

image.export_pixels(x=0, y=0, columns=image.columns, rows=image.rows, map="RGB") -> anArray

#### Description

Extracts the pixel data from the specified rectangle and returns it as an array of `Integer` values.

The array returned by `export_pixels` is suitable for use as an argument to `import_pixels`.

#### Arguments

x, y
  The offset of the rectangle from the upper-left corner of the image.
columns, rows
  The width and height of the rectangle.
map
  A string that describes which pixel channel data is desired and the order in which it should be stored. It can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow, M = magenta, K = black, I = intensity (for grayscale), or P = pad.

#### Returns

An array

#### Example

    # Export the r'th scanline from an image in red-green-blue order
    scanline = img.export_pixels(0, r, img.columns, 1, "RGB");

#### See also

dispatch, export_pixels_to_str, import_pixels, get_pixels

#### Magick API

ExportImagePixels

#### Note

This method replaces the `dispatch` method.

### export_pixels_to_str

image.export_pixels_to_str(x=0, y=0, columns=image.columns, rows=image.rows, map="RGB", type=`Magick::CharPixel`) -> aString

#### Description

Extracts the pixel data from the specified rectangle and returns it as a string. If you need to get the pixel data in a memory buffer (as input to another application, for example), this method is much, much faster than export_pixels or get_pixels.

The string returned by `export_pixels_to_str` is suitable for use as an argument to `import_pixels`.

Note: You can also use to_blob to convert an image into a string.

#### Arguments

x, y
  The offset of the rectangle from the upper-left corner of the image.
columns, rows
  The width and height of the rectangle.
map
  A string that describes which pixel channel data is desired and the order in which it should be stored. It can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow, M = magenta, K = black, I = intensity (for grayscale), or P = pad.
type
  A StorageType value that specifies the C datatype to which the pixel data will be converted. The default is `CharPixel`, which means that the pixel values will be stored as C `unsigned char`s.

#### Returns

A string

#### See also

dispatch, export_pixels, import_pixels, get_pixels

#### Magick API

ExportImagePixels

### find_similar_region

image.find_similar_region(target, x=0, y=0) -> [rx, ry]

#### Description

This interesting method searches for a rectangle in the image that is similar to the target. For the rectangle to be similar each pixel in the rectangle must match the corresponding pixel in the target image within the range specified by the `fuzz` attributes of the image and the target image.

#### Arguments

target
  An image that forms the target of the search. This image can be any size.
x, y
  The starting x- and y-offsets for the search. If omitted both x and y default to 0.

#### Returns

If the search succeeds, the return value is an array with 2 elements. These elements are the x- and y-offsets of the matching rectangle. If the search fails the return value is `nil`.

#### Magick API

IsImageSimilar (available in ImageMagick 6.2.8)

### flip

image.flip -> anImage

#### Description

Create a vertical mirror image of the receiver.

#### Returns

A new image

#### Example

#### See also

affine_transform, flip!, flop, rotate, transpose, transverse

#### Magick API

FlipImage

### flip!

image.flip! -> image

#### Description

In-place form of flip.

#### Returns

self

### flop

image.flop -> anImage

#### Description

Create a horizontal mirror image of the receiver.

#### Returns

A new image

#### Example

#### See also

affine_transform, flip, flop!, rotate, transpose, transverse

#### Magick API

FlopImage

### flop!

image.flop! -> image

#### Description

In-place form of flop.

#### Returns

self

### frame

image.frame(width=25, height=25, x=25, y=25, inner_bevel=6, outer_bevel=6, color=`matte_color`) -> anImage

#### Description

Adds a simulated 3D border.

#### Arguments

width
  The width of the left and right sides.
height
  The height of the top and bottom sides.
x, y
  The image does not have to be centered in the border. These two arguments specify the offset of the image from the upper-left outside corner of the border.
inner_bevel, outer_bevel
  The width of the inner and outer shadows of the border. These values should be much smaller than the width and height and cannot be greater than 1/2 the lesser of the width or height.
color
  The border color. By default the color is the matte color.

#### Returns

A new image

#### Example

#### See also

border

#### Magick API

FrameImage

### freeze

image.freeze -> self

#### Description

Prevent further modifications to the image.

#### Returns

self

### gamma_channel

image.gamma_channel(gamma, [channel...]) = anImage

#### Description

Gamma-correct a particular image channel. The same image viewed on different devices will have perceptual differences in the way the image's intensities are represented on the screen.

#### Arguments

gamma
  Values typically range from 0.8 to 2.3. You can also reduce the influence of a particular channel with a gamma value of 0.
channel...
  0 or more ChannelType arguments. If no channels are specified, all the channels are corrected using the gamma value.

#### Returns

A new image

#### See also

The older gamma_correct method is implemented in terms of `gamma_channel`.

#### Magick API

GammaImageChannel

### gamma_correct

image.gamma_correct(red_gamma[,green_gamma[, blue_gamma]]) -> anImage

#### Description

Gamma-correct an image. The same image viewed on different devices will have perceptual differences in the way the image's intensities are represented on the screen.

#### Arguments

You must specify at least `red_gamma`. Omitted arguments take on the value of the last specified argument. Values typically range from 0.8 to 2.3.

#### Returns

A new image

#### See also

gamma_channel

#### Magick API

GammaImage

### gaussian_blur

image.gaussian_blur(radius=0.0, sigma=1.0) -> anImage

#### Description

Blurs an image. We convolve the image with a Gaussian operator of the given radius and standard deviation (sigma).

#### Arguments

radius
  A `Float` value representing the radius of the Gaussian, in pixels, not counting the center pixel.
sigma
  A `Float` value representing the standard deviation of the Gaussian operator, in pixels. This argument must be > 0.0.

#### Returns

A new image

#### Example

`gaussian_blur(0.0, 3.0)`

#### See also

blur_image, motion_blur, radial_blur

#### Magick API

GaussianBlurImage

### gaussian_blur_channel

image.gaussian_blur_channel(radius=0.0, sigma=1.0[, channel...]) -> anImage

#### Description

Blurs the selected channel or channels using a Gaussian operator of the specified radius and standard deviation.

#### Arguments

radius
  A `Float` value representing the radius of the Gaussian, in pixels, not counting the center pixel.
sigma
  A `Float` value representing the standard deviation of the Gaussian operator, in pixels. This argument must be > 0.0.
channel...
  0 or more ChannelType arguments. If no channels are specified, all the channels are blurred. This is the same as using gaussian_blur.

#### Returns

A new image

#### See also

blur_channel

#### Magick API

GaussianBlurImageChannel (available in ImageMagick 6.0.0)

### get_exif_by_entry

image.get_exif_by_entry([name]*) -> anArray

#### Description

Returns the value associated with the specified EXIF entry name or names. If no names are specified, returns all the entries. The return value is an array containing one or more [name, value] elements.

#### Arguments

Zero or more EXIF entry names.

#### Returns

The elements in the returned array are 2-element arrays in the form [name, value]. If ×Magick does not know the name for an entry it uses "unknown." There may be more than one entry for "unknown" in the returned array. If there is no entry with the specified name the value is set to `nil`.

#### Example

    image.get_exif_by_entry('Make') » [["Make", "Canon"]]
    image.get_exif_by_entry("ShutterSpeedValue") »
        [["ShutterSpeedValue", "189/32"]]
    image.get_exif_by_entry() »
        [["Make", "Canon"], ["ShutterSpeedValue", "189/32"] ...]

#### See also

get_exif_by_number

### get_exif_by_number

image.get_exif_by_number([tag]*) -> aHash

#### Description

Returns the value associated with the specified EXIF tag number or numbers. If no numbers are specified, returns all the tags. The return value is a hash. The hash keys are EXIF tag numbers. The values are the values associated with the tags.

#### Arguments

Zero or more EXIF tag numbers.

#### Returns

A hash. If there is no tag with the specified number the value is set to `nil`.

#### Example

    image.get_exif_by_number(271) » {271=>"Canon"}
    image.get_exif_by_number(37377) » {37377=>"189/32"}
    image.get_exif_by_number() »
        {271=>"Canon", 37377=>"189/32" ...}

#### See also

get_exif_by_entry

### get_iptc_dataset

image.get_iptc_dataset(ds) -> aString

#### Description

Retrieves the data field for the specified DataSet, or `nil` if the DataSet is not used or the data field has length 0.

#### Arguments

RMagick defines the following constants for use as arguments to this method. All the constants are in the Magick::IPTC namespace. Notice that some DataSets have two names.

Constant | Record:DataSet
--- | ---
Envelope::Model_Version | 1:00
Envelope::Destination | 1:05
Envelope::UNO | 1:100
Envelope::Unique_Name_of_Object | 1:100
Envelope::ARM_Identifier | 1:120
Envelope::ARM_Version | 1:122
Envelope::File_Format | 1:20
Envelope::File_Format_Version | 1:22
Envelope::Service_Identifier | 1:30
Envelope::Envelope_Number | 1:40
Envelope::Product_ID | 1:50
Envelope::Envelope_Priority | 1:60
Envelope::Date_Sent | 1:70
Envelope::Time_Sent | 1:80
Envelope::Coded_Character_Set | 1:90
Application::Object_Type_Reference | 2:03
Application::Object_Name | 2:05
Application::Title | 2:05
Application::Edit_Status | 2:07
Application::Editorial_Update | 2:08
Application::Urgency | 2:10
Application::Country_Primary_Location_Code | 2:100
Application::Country_Primary_Location_Name | 2:101
Application::Original_Transmission_Reference | 2:103
Application::Headline | 2:105
Application::Credit | 2:110
Application::Source | 2:115
Application::Copyright_Notice | 2:116
Application::Contact | 2:118
Application::Subject_Reference | 2:12
Application::Abstract | 2:120
Application::Caption | 2:120
Application::Caption_Writer | 2:122
Application::Editor | 2:122
Application::Rasterized_Caption | 2:125
Application::Image_Type | 2:130
Application::Image_Orientation | 2:131
Application::Language_Identifier | 2:135
Application::Category | 2:15
Application::Audio_Type | 2:150
Application::Audio_Sampling_Rate | 2:151
Application::Audio_Sampling_Resolution | 2:152
Application::Audio_Duration | 2:153
Application::Audio_Outcue | 2:154
Application::Supplemental_Category | 2:20
Application::ObjectData_Preview_File_Format | 2:200
Application::ObjectData_Preview_File_Format_Version | 2:201
Application::ObjectData_Preview_Data | 2:202
Application::Fixture_Identifier | 2:22
Application::Keywords | 2:25
Application::Content_Location_Code | 2:26
Application::Content_Location_Name | 2:27
Application::Release_Date | 2:30
Application::Release_Time | 2:35
Application::Expiration_Time | 2:35
Application::Expiration_Date | 2:37
Application::Special_Instructions | 2:40
Application::Action_Advised | 2:42
Application::Reference_Service | 2:45
Application::Reference_Date | 2:47
Application::Reference_Number | 2:50
Application::Date_Created | 2:55
Application::Time_Created | 2:60
Application::Digital_Creation_Date | 2:62
Application::Digital_Creation_Time | 2:63
Application::Originating_Program | 2:65
Application::Program_Version | 2:70
Application::Object_Cycle | 2:75
Application::Author | 2:80
Application::By_Line | 2:80
Application::Author_Position | 2:85
Application::By_Line_Title | 2:85
Application::City | 2:90
Application::Sub_Location | 2:92
Application::Province | 2:95
Application::State | 2:95
Pre_ObjectData_Descriptor::Size_Mode | 7:10
Pre_ObjectData_Descriptor::Max_Subfile_Size | 7:20
Pre_ObjectData_Descriptor::ObjectData_Size_Announced | 7:90
Pre_ObjectData_Descriptor::Maximum_ObjectData_Size | 7:95
ObjectData::Subfile | 8:10
Post_ObjectData_Descriptor::Confirmed_ObjectData_Size | 9:10

#### Example

    img.get_iptc_dataset(Magick::IPTC::Application::Keywords)

#### Returns

The data field or nil

#### See also

each_iptc_dataset, iptc_profile

### get_pixels

image.get_pixels(x, y, columns, rows) -> anArray

#### Description

Gets the pixels from the specified rectangle within the image.

#### Arguments

x, y
  The x- and y-offset of the rectangle within the image.
columns, rows
  The width and height of the rectangle.

#### Returns

An array of pixels. There will be `columns*rows` elements in the array.

#### Example

This example composites a black-and-white version of an image over the same image in its original colors. It uses `get_pixels` and store_pixels to make each column of pixels in the black-and-white image slightly more opaque than the column on its left, so that the resulting composite changes smoothly from color on the left to black-and-white on the right.

#### See also

store_pixels, view

#### Magick API

AcquireImagePixels

### gray?

image.gray? -> `true` or `false`

#### Description

Returns `true` if all the pixels in the image have the same red, green, and blue intensities.

#### Returns

`true` or `false`

#### See also

monochrome?

#### Magick API

IsGrayImage

### grayscale_pseudo_class

image.grayscale_pseudo_class(optimize=`true`) -> anImage

#### Description

Converts an image to a PseudoClass grayscale representation with an optionally compressed and sorted colormap.. This method is only available in GraphicsMagick 1.1 and later.

#### Arguments

optimize
  If true, compress and sort the colormap by increasing intensity.

#### Returns

A new image

#### Magick API

GrayscalePseudoClass

### grey?

image.qrey? -> `true` or `false`

#### Description

Synonym for gray?

### implode

image.implode(amount=0.50) -> anImage

#### Description

A funhouse mirror effect. See the example below.

#### Arguments

A `Float` value. Increasing the absolute value of the argument increases the effect. The value may be positive for implosion, or negative for explosion. The default is 0.50.

#### Returns

A new image

#### Example

This example is an animated image. Mouse over the image to start the animation.

#### Magick API

ImplodeImage

### import_pixels

image.import_pixels(x, y, columns, rows, map, pixels, type=Magick::CharPixel) -> image

#### Description

Replaces the pixels in the specified rectangle with pixel data from the supplied array or string. When the pixels argument is an array of pixel data, this method is the reverse of `export_pixels`. When the pixels argument is a string, `import_pixels` is ideal for loading very large amounts of binary pixel data.

#### Arguments

x, y
  The offset of the rectangle from the upper-left corner of the image
columns, rows
  The width and height of the rectangle
map
  A string describing the expected ordering of the pixel array. It can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow, M = magenta, K = black, or I = intensity (for grayscale).
pixels
  The pixel data. Pixel data can be supplied as an array or as a string.
  If pixels responds to `:to_str`
    `import_pixels` assumes that pixels can be converted to a string by `to_str` and that the result is a C array of the type specified by type containing binary pixel data in the order specified by map. The elements in the buffer must be in the range specified by type.
  Otherwise
    `import_pixels` assumes that pixels is an array or an object that can be converted to an array by the `Kernel::Array` method. The elements in the array must be `Numeric` values in the range [0..MaxRGB]. In either case, the pixel data must be stored in scanline order: left-to-right and top-to-bottom.
type
  A StorageType value that specifies the type and range of the pixel data when pixels is a string.

#### Returns

The image as transformed by the pixel data.

#### Example

    # Replace the r'th scanline of the image using
    # pixel data stored in red-green-blue order.
    img.import_pixels(0, r, img.columns, 1, "RGB", scanline);

#### Example

This example is contrived since there's no need to convert the `pixels` array into a string by calling `pack`, but it does demonstrate the use of a string pixels argument. Note that this example assumes that ×Magick is configured with QuantumDepth=8.

    hat = Magick::Image.read("Flower_Hat.jpg").first
    pixels = hat.export_pixels(0, 0, hat.columns, hat.rows, "RGB")
    char_buffer = pixels.pack("C*")
    img = Magick::Image.new(hat.columns, hat.rows)
    img.import_pixels(0, 0, hat.columns, hat.rows, "RGB", char_buffer, Magick::CharPixel)

#### See also

constitute, export_pixels, store_pixels

#### Magick API

ImportImagePixels

#### Note

This method replaces the `constitute` method.

### inspect

image.inspect -> aString

#### Description

Constructs a description of the image as a string. The string contains some or all of the following fields:

original_filename=>
  if different from the current filename.
filename
  the current filename
[scene]
  the scene number, if the image is part of an image sequence
format
  the image format (GIF or JPEG, for example)
original width x height
  if different from the current width x height
page width x height + x-offset + y-offset
  if any of these fields is non-zero
storage class
  DirectClass or PseudoClass
number of colors
  total number of colors used in the image
mean error per pixel/normalized mean error/normalized maximum error
  for PseudoClass images, if present
N-bit
  bit depth
blob size
  if present

#### Example

    f.inspect » "images/Flower_Hat.jpg JPEG 200x250 DirectClass 8-bit 9kb"

### level

image.level(black_point=`0.0`, white_point=`MaxRGB`, gamma=`1.0`) -> anImage

#### Description

Adjusts the levels of an image by scaling the colors falling between specified white and black points to the full available quantum range. The parameters provided represent the black, mid, and white points. The black point specifies the darkest color in the image. Colors darker than the black point are set to zero. Gamma specifies a gamma correction to apply to the image. White point specifies the lightest color in the image. Colors brighter than the white point are set to the maximum quantum value

#### Arguments

black_point
  A black point level in the range 0-MaxRGB. The default is 0.0.
mid_point
  A white point level in the range 0-MaxRGB. The default is MaxRGB - black_point.
gamma
  A gamma correction in the range 0.0-10.0 The default is 1.0.

#### Returns

A new image

#### Example

`level(0,1.50)`

#### Compatibility notes

Prior to version 1.11.0 RMagick defined the signature for `level` incorrectly:

    img.level(white_point, gamma, black_point) -> anImage # wrong!

That is, the `gamma` and `white_point` arguments were swapped. In an effort to maintain compatiblity with older scripts that expect that signature, `level` inspects its arguments and will interchange `white_point` and gamma if they "look" incorrect. That is, if `gamma` is > 10.0, or if `white_point` is < 10.0, or if `gamma` > `white_point`, then `level` will swap them.

If you want to avoid this behavior, use the `level2` method instead. The `level2` method is exactly the same as `level` except that it never swaps the arguments.

#### See also

level_channel

#### Magick API

LevelImage

### level_channel

image.level_channel(channel, black_point=0, white_point=MaxRGB - black_point, gamma=1.0) -> anImage

#### Description

Same as level but operates only on the specified channel.

#### Arguments

channel
  A ChannelType value.
black_point
  A black point level in the range 0-MaxRGB. The default is 0.0.
mid_point
  A white point level in the range 0-MaxRGB. The default is MaxRGB - black_point.
gamma
  A gamma correction in the range 0.0-10.0 The default is 1.0.

#### Returns

A new image

#### See also

level

#### Magick API

LevelImageChannel

### magnify

image.magnify -> anImage

#### Description

A convenience method that scales the receiver to twice its size.

#### Returns

A new image

#### See also

magnify!, minify, resize, scal

#### Magick API

MagnifyImage

### magnify!

image.magnify! -> image

#### Description

In-place form of magnify

#### Returns

self

### map

image.map(img, dither=false) -> anImage

#### Description

Replaces the colors of an image with the closest color from a reference image.

#### Arguments

img
  The reference image. May be either another image or an Image object.
dither
  If true, dithers the mapped image.

#### Returns

A new image

#### Example

This image has been mapped to the Netscape 216-color cube.

#### See also

ImageList#map

#### Magick API

MapImage

### matte_fill_to_border

image.matte_fill_to_border(x, y) -> anImage

#### Description

Makes transparent all the pixels that are neighbors of the pixel at x,y and are not the border color.

#### Arguments

The x- and y- coordinates of the target pixel.

#### Returns

A new image

#### Example

In this example the border color is black. The fill starts in the center and makes all the pixels transparent until it reaches a black pixel. The resulting image has been composited over a plasma background, which shows through the transparent pixels.

#### See also

matte_floodfill, Draw#matte

#### Magick API

MatteFloodfillImage

### matte_floodfill

image.matte_floodfill(x, y) -> anImage

#### Description

Makes transparent all the pixels that are the same color as the pixel at x, y, and are neighbors.

#### Arguments

The x- and y-coordinates of the target pixel.

#### Returns

A new image

#### Example

In this example the fill starts at the center pixel and replaces all the yellow pixels - the color of the center pixel. The resulting image has been composited over a plasma background, which shows through the transparent pixels.

#### See also

matte_replace, Draw#matte

#### Magick API

MatteFloodfilImage

### matte_point

image.matte_point(x, y) -> anImage

#### Description

Makes the pixel at x, y transparent. This method makes a copy of the image, just to make one pixel transparent. I recommend using the Draw#matte method instead.

#### Arguments

The x- and y-coordinates of the target pixel.

#### Returns

A new image

#### See also

Draw#matte

### matte_replace

image.matte_replace(x, y) -> anImage

#### Description

Makes transparent all the pixels that are the same color as the pixel at x, y.

#### Arguments

The x- and y-coordinates of the target pixel.

#### Returns

A new image

#### Example

In this example the target pixel is a black pixel in the center of the uppermost circle. The matte_replace method makes all the black pixels in the image transparent. The resulting image has been composited over a plasma background, which shows through the transparent pixels.

#### See also

transparent, Draw#matte

#### Magick API

TransparentImage

### matte_reset!

image.matte_reset! -> image

#### Description

Makes all the pixels in the image transparent.

#### Returns

self

#### See also

opacity=

#### Magick API

SetImageOpacity

### median_filter

image.median_filter(radius=1.0) -> anImage

#### Description

Applies a digital filter that improves the quality of a noisy image. Each pixel is replaced by the median in a set of neighboring pixels as defined by radius.

#### Arguments

The filter radius. The larger the value, the longer it takes to render. Values larger than 8 or 9 may take longer than you want to wait, and will not have significantly better results than much smaller values.

#### Returns

A new image

#### Example

The left side of the image has been modified by add_noise. The right side has been filtered by median_filter(0.05).

#### See also

enhance, reduce_noise, unsharp_mask

#### Magick API

MedianFilterImage

### minify

image.minify -> anImage

#### Description

A convenience method that scales the receiver to half its size.

#### Returns

A new image

#### See also

minify! magnify, resize, sample, scale, thumbnail

#### Magick API

MinifyImage

### minify!

image.minify! -> image

#### Description

In-place form of minify.

#### Returns

self

### modulate

image.modulate(brightness=1.0, saturation=1.0, hue=1.0) -> anImage

#### Description

Changes the brightness, saturation, and hue.

#### Arguments

The percent change in the brightness, saturation, and hue, represented as Float numbers. For example, 0.25 means "25%". All three arguments may be omitted. The default value of each argument is 1.0, that is, 100%.

#### Returns

A new image

#### Example

modulate(0.85)

#### Magick API

ModulateImage

### monochrome?

image.monochrome? -> true or false

#### Description

Returns true if all the pixels have the same red, green, and blue values and the values are either 0 or MaxRGB. That is, the image is black-and-white.

#### See also

gray?

#### Magick API

IsMonochromeImage

### motion_blur

image.motion_blur(radius=0.0, sigma=1.0, angle=0.0) -> anImage

#### Description

Simulates motion blur. We convolve the image with a Gaussian operator of the given radius and standard deviation (sigma). Use a radius of 0 and motion_blur selects a suitable radius for you. Angle gives the angle of the blurring motion.

#### Arguments

radius
  The radius of the Gaussian operator.
sigma
  The standard deviation of the Gaussian operator. Must be non-0.
angle
  The angle (in degrees) of the blurring motion.

#### Returns

A new image

#### Example

#### See also

blur_image, gaussian_blur

#### Magick API

MotionBlurImage

### negate

image.negate(grayscale=false) -> anImage

#### Description

Negates the colors in the receiver.

#### Arguments

If the grayscale argument is true, only the grayscale values are negated.

#### Returns

A new image

#### Example

#### See also

negate_channel

#### Magick API

NegateImage

### negate_channel

image.negate_channel(grayscale=false, [channel...]) = anImage

#### Description

Negate a particular image channel or channels.

#### Arguments

grayscale
  if true, only negate grayscale pixels within the image
channel...
  0 or more ChannelType arguments. If no channels are specified, all the channels are negated. Specifying no channel arguments has the same effect as the negate method, above.

#### Returns

A new image

#### Example

negate_channel(false, GreenChannel)

#### See also

negate

.

#### Magick API

NegateImageChannel

### normalize

image.normalize -> anImage

#### Description

Enhances the contrast of a color image by adjusting the pixel color to span the entire range of colors available.

#### Returns

A new image

#### Example

#### Magick API

NormalizeImage

#### See also

normalize_channel

### normalize_channel

image.normalize_channel([channel...]) = anImage

#### Description

Enhances the contrast of a color image by adjusting the pixel color to span the entire range of colors available. Only the specified channels are normalized.

#### Arguments

channel...
  0 or more ChannelType arguments. If no channels are specified, all the channels are normalized. Specifying no channel arguments has the same effect as the normalize method, above.

#### Returns

A new image

#### Magick API

NormalizeImageChannel (available in ImageMagick 6.1.0)

#### See also

normalize

### oil_paint

image.oil_paint(radius=3.0) -> anImage

#### Description

Applies a special effect filter that simulates an oil painting. Each pixel is replaced by the most frequent color occurring in a circular region defined by radius.

#### Returns

A new image

#### Example

#### Magick API

OilPaintImage

### opaque

image.opaque(target, fill) -> anImage

#### Description

Changes all pixels having the target color to the fill color.

#### Arguments

target
  The color to be replaced. May be a color name or a Pixel
fill
  The replacement color. May be a color name or a Pixel

#### Returns

A new image

#### Example

    img.fuzz = 25
    img = img.opaque('white', 'red')

#### See also

color_floodfill

#### Magick API

OpaqueImage

### opaque?

image.opaque? -> true or false

#### Description

Returns true if all of the pixels in the receiver have an opacity value of OpaqueOpacity.

#### Returns

true or false

#### Magick API

IsOpaqueImage

### ordered_dither

image.ordered_dither(order=2) -> anImage

#### Description

Uses the ordered dithering technique of reducing color images to monochrome using positional information to retain as much information as possible.

#### Arguments

order
  The dither order. Must be one of the integers 2, 3, or 4.

#### Returns

A new image

#### Example

#### See also

posterize, quantize

#### Magick API

RandomThresholdImageChannel

### palette?

image.palette? -> true or false

#### Description

Returns true if the image is PseudoClass and has 256 unique colors or less.

#### Returns

true or false

#### Magick API

IsPaletteImage

### pixel_color

image.pixel_color(x, y[, new_color]) -> aPixel

#### Description

Returns the color of the pixel at x, y. Optionally, changes the color of the pixel to a new color.

If new_color is specified, pixel_color changes the image type to DirectClass if necessary.

#### Arguments

x, y
  The x- and y-coordinates of the pixel.
new_color
  If specified, the pixel is set to this color. May be either a color name or a Pixel.

#### Returns

A Pixel having the RGB values of the specified pixel.

#### Example

    old = image.pixel_color(20,40,"white")

#### Magick API

AcquireImagePixels

### posterize

image.posterize(levels=4, dither=false) -> anImage

#### Description

Reduces the image to a limited number of colors for a "poster" effect.

#### Arguments

levels
  Number of color levels allowed in each channel. Very low values (2, 3, or 4) have the most visible effect. The default is 4.
dither
  If true, dither the image. The default is false.

#### Returns

A new image

#### Example

#### See also

ordered_dither, quantize

#### Magick API

PosterizeImage