Miscellaneous classes

Table of Contents

The Image::View class

The Geometry class

The Pixel class

Struct classes

Fill classes

Exception classes

The Image::View class

Introduction

A view is a rectangle in an image. Within the view pixels can be addressed by specifying their [i][j] coordinates. The i, j index values can identify a single pixel or multiple pixels. Pixels can be accessed or modified individually or collectively. Pixel channels (that is, the red, green, blue, and opacity components) can be accessed or modified individually or collectively. The sync method stores modified pixels back into the image.

class Image::View < Object

new

Image::View.new(img, x, y, width, height) -> view

Description

The easiest way to use an Image::View object is to create it with the Image#view method, which provides a block-scoped view and automatic syncing. You probably won't want to create a view by calling new.

Arguments
img
The image from which the view is taken.
x, y
The x- and y-offsets of the view relative to the top-left corner of the image. Within the view, pixel addresses are relative to the top-left corner of the view.
width, height
The number of columns and the number of rows in the view.

It is an error to specify a view that exceeds the boundaries of the image.

[][]

view[i][j] -> pixel or array

Description

Return one or more pixels in the view. If i and j are each a single integer value, returns a single pixel. For any other indexes, returns an array of one or more pixels. If any index exceeds the boundaries of the view, raises IndexError.

Arguments

The i index identifies a set of rows in the view. The j index identifies a set of columns in the view. The pixels that are returned are the intersection of these two sets. The indexes can be:

omitted
If i is omitted, all the rows are used. If j is omitted, all the columns are used.
an integer
or an object that can be converted to an integer. A single integer identifies a single row or column. Identify a single pixel by specifying integers for both indexes. If the index is negative, counts from the bottom row or right column of the view.
start, length
Identifies the set of length rows or columns starting with start. If start is negative, starts at the bottom row or right column of the view.
an object that responds to each
The index may be any object that responds to each by returning a sequence of objects that can be converted to integers. An array with integer values or a range of integers are two examples.
Examples
  # Get the 2nd pixel in the 4th row of the view.
  pixel = view[3][1]  # returns a pixel
  # Returns an array with only one value
  pixels = view[[3]][[1]]
  # Get all the pixels in the 4th row
  pixels = view[3][]
  # Use arrays to specify a non-contiguous set of rows and columns
  pixels = view[[1,3,5]][[2,4,6]]
  # Use ranges to specify a contiguous set of rows and columns
  pixels = view[1..5][2..6]

[][].red
[][].green
[][].blue
[][].opacity

[i][j].red -> integer or array
[i][j].green -> integer or array
[i][j].blue -> integer or array
[i][j].opacity -> integer or array

Description

If the indexes identify a single pixel, these methods return the value of the red, green, blue, or opacity channel of that pixel. If the indexes identify more than one pixel, these methods return an array of values. See [][] for a description of possible index arguments.

Examples
  # Get the value of the green channel of
  # the top-left pixel in the view.
  view[0][0] = Pixel(0,128,255)
  g = view[0][0].green  # returns 128

  # Get the maximum value of the red channel
  # for all the pixels in the top row of the view.
  m = view[0][].red.max

[][]=

view[i][j] = rvalue

Description

Replaces each pixel identified by the indexes with a duplicate of rvalue. The rvalue is either a Pixel object or a color name. If rvalue is a color name, calls Pixel.from_color to create a pixel.

Arguments

The indexes are the same as [][], above.

rvalue
Either a pixel or a color name.

[][].red=
[][].green=
[][].blue=
[][].opacity=

[i][j].red = integer
[i][j].green = integer
[i][j].blue = integer
[i][j].opacity = integer

Description

Assigns integer to the red, green, blue, or opacity channel of the pixel or pixels identified by the indexes.

Examples
  # Set the red channel of all the pixels in the 2nd
  # row of the view to QuantumRange
  view[1][].red = QuantumRange
  # Set the green channel of the pixel at [20][30] to
  # half that of its left-hand neighbor.
  view[20][30].green = view[20][29].green * 0.5

sync

view.sync(force=false) -> true or false

Description

If any of the pixels in the view have been modified, this method stores them in the image. If no pixels have been modified, this method has no effect.

Arguments
force
If true, forces the view pixels to be stored in the image even if none have been modified.
Returns
Returns true if the pixels were stored in the image either because the dirty flag was true or force was true, false otherwise.

dirty
dirty=

view.dirty -> true or false
view.dirty = true or false

Description

Any modification to a pixel in the view causes the dirty attribute to be set to true. You can (although normally you don't need to) set dirty=true to force sync to store the pixels in the image, or set dirty=false to keep sync from storing the pixels.

x
y
width
height

x -> integer
y -> integer
width -> integer
height -> integer

Description

The x, y, width, and height arguments specified when the view was created.

The Geometry class

Introduction

The Geometry class contains the same information as an ImageMagick geometry string. Geometry objects are interchangeable with geometry strings.

class Geometry < Object

new

Geometry.new(width=nil, height=nil, x=nil, y=nil, flag=nil) -> geometry

Description

Constructs a new Geometry object.

Attributes

A geometry string has the general form "WxH+x+y[!@%<>]. In a Geometry object,

width
specifies the W value
height
specifies the H value
x, y
specify the x and y values, respectively
flag
one of the constants shown in this table:
Geometry flag constants
Constant
name
Geometry
string flag
Explanation
PercentGeometry % Normally the attributes are treated as pixels. Use this flag when the width and height attributes represent percentages. For example, 125x75 means 125% of the height and 75% of the width. The x and y attributes are not affected by this flag.
AspectGeometry ! Use this flag when you want to force the new image to have exactly the size specified by the the width and height attributes.
LessGeometry < Use this flag when you want to change the size of the image only if both its width and height are smaller the values specified by those attributes. The image size is changed proportionally.
GreaterGeometry > Use this flag when you want to change the size of the image if either its width and height exceed the values specified by those attributes. The image size is changed proportionally.
AreaGeometry @ This flag is useful only with a single width attribute. When present, it means the width attribute represents the total area of the image in pixels.
MinimumGeometry ^ Use ^ to set a minimum image size limit. The geometry 640x480^, for example, means the image width will not be less than 640 and the image height will not be less than 480 pixels after the resize. One of those dimensions will match the requested size, but the image will likely overflow the space requested to preserve its aspect ratio.

If any attribute is omitted the default is nil or 0.

Example
g = Magick::Geometry.new(100,200,nil,nil,Magick::AspectGeometry)

from_s

Geometry.from_s(string) -> geometry

Description

Constructs a new Geometry object from a geometry string.

to_s

geom.to_s() -> string

Description

Returns the string equivalent of the Geometry object..

The Pixel class

Introduction

A pixel describes the smallest individually addressable part of an image. In the RGB colorspace, a pixel's color is described by its intensity in the red, green, and blue channels. Its opacity is described by its intensity in the opacity (also called alpha, or matte) channel. In the CMYK colorspace a pixel's color is described by its intensity in the cyan, magenta, yellow and black (K) channels. Intensity is a value between 0 and QuantumRange.

Usually, RMagick methods operate on entire images or on groups of pixels that have been selected by their position or color. Some methods, such as pixel_color and view, operate on individual pixels or even on the RGBA (or CMYK) components thereof.

class Pixel < Object
mixes in Comparable, Observable

new

Pixel.new(red, green, blue, opacity) -> pixel

Description

Constructs a pixel object from the specified red, green, blue, and opacity intensities. The intensity is a number between 0 and QuantumRange.

Attributes
red, green, blue
The red, green, and blue intensities of the pixel, respectively. If the colorspace is CMYKColorspace, these attributes are interpreted as the cyan, magenta, and yellow intensities.
opacity
The opacity level. Higher intensities are more transparent. If the colorspace is CMYKColorspace, this attribute is interpreted as the black intensity.
cyan, magenta, yellow, black
These attributes are aliases for red, green, blue, and opacity, respectively.

from_color

Pixel.from_color(color_name) -> pixel

Description

Constructs a new Pixel object from the color name. Raises ArgumentError if the name is unknown.

from_hsla

Pixel.from_hsla(hue, saturation, lightness, alpha=1.0) -> pixel

Description

Constructs a pixel object from the specified arguments.

Arguments
hue
Either a String percentage (e.g., "25%") or a value in the range [0.0, 360.0).
saturation
Either a String percentage (e.g., "25%") or a value in the range [0.0, 255.0].
lightness
Either a String percentage (e.g., "25%") or a value in the range [0.0, 255.0].
alpha
Either a String percentage (e.g., "25%") or a value in the range [0.0, 1.0], where 1.0 is fully opaque and 0.0 is fully transparent. This argument may be omitted. The default is 1.0.
See also

to_hsla

<=>

pixel1 <=> pixel2 -> -1, 0, or 1

Description

Returns -1, 0, or 1 depending on if pixel1 is "less than," equal, or "greater than" the pixel2.

Since there is no way to rank order pixels, and thus determine if one pixel is "greater than" or "less than" another, this method uses an arbitrary algorithm that ensures these two conditions:

  1. pixels with equal RGBA (or CMYK) values compare equal, and
  2. comparing the same two unequal pixels always returns the same result.
Returns

-1, 0, or 1

See also

fcmp

fcmp

pixel.fcmp(pixel, fuzz=0.0, colorspace=RGBColorspace) -> true or false

Description

Returns true if the argument is the same color as pixel.

Arguments
pixel
The pixel to which the receiver is compared.
fuzz
The amount of fuzz to allow before the colors are considered to be different.
colorspace
If the pixels are in the CMYK colorspace, specify Magick::CMYKColorspace.
Returns

true or false

See also

<=>

intensity

pixel.intensity() -> integer

Description

Returns the intensity of the pixel. The intensity is computed as 0.299*R+0.587*G+0.114*B.

to_color

pixel.to_color(compliance=AllCompliance, matte=false, depth=QuantumDepth, hex=false) -> string

Description

Returns the color name corresponding the the pixel values. If there is no such named color in the specified color standard, returns a string in the form "rgb(r,g,b,a)".

Arguments
compliance
A ComplianceType constant. The default value of AllCompliance causes to_color to search for a color name in any of the 3 defined color standards.
matte
If false, the pixel's opacity attribute is ignored.
depth
An image depth. The default is the quantum depth used when ImageMagick was compiled. The values 16 and 32 can be used only when ImageMagick was compiled with the appropriate QuantumDepth.
hex
If true, represent the color name in hex (#rrggbbaa or #rrrrggggbbbbaaaa) format. In this case compliance is meaningless.
See also

Compare this method to Image#to_color, in which the matte and depth values are taken from an image.

to_hsla

pixel.to_HSL -> array

Description

Converts the RGB representation of the pixel to hue, saturation, lightness, and alpha values.

Returns

An array of the form [hue, saturation, lightness, alpha]. Each value is in the range specified for it, as described in from_hsla, above.

Struct classes

Introduction

These classes are created by the Struct class and are used to create objects used as attribute and argument values in other RMagick classes. Like all the classes created by Struct, these classes define both getter and setter methods for their attributes. That is, for an attribute x both the x and x= methods are defined.

The Pixel and Geometry classes define additional constructors and conversion methods.

class AffineMatrix < Struct

new

AffineMatrix.new(sx, rx, ry, sy, tx, ty) -> matrix

Description

An AffineMatrix object describes a coordinate transformation. This object is used as an argument to the Image#affine_transform, Image#composite_affine, and Draw#affine methods.

Attributes
sx, sy
The amount of scaling on the x- and y- axes.
rx, ry
The amount of rotation on the x- and y-axes, in radians.
tx, ty
The amount of translation on the x- and y-axes, in pixels.

class Chromaticity < Struct

new

Chromaticity.new(red_primary, green_primary, blue_primary, white_point) -> chromaticity

Description

A Chromaticity object represents chromaticity values for the Image#chromaticity attribute.

Attributes

The attribute values are Primary objects.

red_primary
Red primary point (e.g. red_primary.x=0.64, red_primary.y=0.33)
green_primary
Green primary point (e.g. green_primary.x=0.3, green_primary.y=0.6)
blue_primary
Blue primary point (e.g. blue_primary.x=0.15, blue_primary.y=0.06)
white_point
White point (e.g. white_point.x=0.3127, white_point.y=0.329)

class Point < Struct

new

Point.new(x, y) -> point

Description

The value of the pixels_per_em attribute in the TypeMetric struct returned by Draw#get_type_metrics is a Point object..

Attributes
x
Character width
y
Character height

class Primary < Struct

new

Primary.new(x, y, z) -> primary

Description

See class Chromaticity.

Attributes
x
X ordinate
y
Y ordinate
z
Z ordinate. This attribute is always ignored.

class Rectangle < Struct

new

Rectangle.new(width, height, x, y) -> rectangle

Description

The value of the Image#tile_info and Image#bounding_box attributes.

Attributes
width
Rectangle width
height
Rectangle height
x
Offset from the left edge of the image
y
Offset from the top edge of the image

class Segment < Struct

new

Segment.new(x1, y1, x2, y2) -> segment

Description

The value of the bounds attribute in the TypeMetric class.

Attributes

x1, y1, x2, y2

Fill classes

Introduction

The Image#new and ImageList#new_image methods accept a Fill object as an optional third argument. A Fill object is an instance of a Fill class. Fill classes are designed to support custom background fills. Each Fill class defines only two methods, initialize and fill. The initialize method is called from the application to create an instance of the fill class. It accepts any arguments and does whatever is necessary to create the fill. The fill method is called from the initialize method of the new image object, after the image is completely initialized. The fill method gets the image as its only argument and sends whatever methods are necessary to the image to fill the image's background.

RMagick supplies three Fill classes, HatchFill, GradientFill, and TextureFill. These classes are explained below. The HatchFill class is intended as an example of how to write a Fill class and is written in pure Ruby. You can read it in RMagick.rb.

class GradientFill < Object

new

GradientFill.new(x1, y1, x2, y2, start_color, end_color) -> gradient_fill

Description

Creates a gradient fill. The x1, y1, and x2, y2 arguments describe either a line or a point. If x1 != x2 or y1 != y2, then the arguments describe the starting line for the gradient. The gradient will start with start_color at the starting line and gradually transform to end_color as the distance increases from the starting line.

If x1 == x2 and y1 == y2, the gradient radiates from the specified point, gradually transforming from start_color to end_color.

The line or point does not have to lie within the image bounds.

Arguments
x1, y1
One of the starting line end-points.
x2, y2
The other end-point on the starting line.
start_color
The color at the starting line.
end_color
The color to which the gradient transforms.
Example

GradientFill example

class HatchFill < Object

new

HatchFill.new(background_color, hatch_color='white', dist=10) -> hatch_fill

Description

Creates a cross-hatched fill.

Arguments

background_color
The image background color.
hatch_color
The color of the cross-hatch lines.
dist
The distance between cross-hatch lines, in pixels.

Example

HatchFill example

class TextureFill < Object

new

TextureFill.new(texture_image) -> texture_fill

Description

Creates a texture fill by tiling the texture_image to fill the image.

Arguments

The texture to be used as the background. May be an image or imagelist. If texture_image is an imagelist, uses the current image.

Example

TextureFill example

Exception classes

class ImageMagickError < StandardError

Description

RMagick raises this exception when an ImageMagick function returns an error condition.

class FatalImageMagickError < StandardError

Description

RMagick raises this exception when ImageMagick raises a fatal (unrecoverable) error condition.

class DestroyedImageError < StandardError

Description

RMagick raises this exception when any Image method (except destroyed? and inspect) is called after an image has been destroyed.