Some Image and ImageList methods,
such as read and write, accept an
"optional arguments" block in which you can set attributes that
modify the method's output. These attributes belong to the
Image::Info class. The Image::Info
class exists only to accept optional arguments for those
Image and ImageList methods.
This page explains the methods defined in the
Image::Info class. Generally, each
Image or ImageList method that uses
the Image::Info class to get optional arguments
will only accept some of the attributes listed on this page,
that is, only those attributes that are meaningful for the
particular method. Any other attributes that you set are
ignored. Also, some attributes are only used by a subset of the
image formats. See the ×Magick documentation for more
information.
Remember, you do not ever need to create an
Image::Info object. The object is created for you
before the optional arguments block is entered and destroyed
after the block is exited.
All the attributes in the Image::Info class are
read/write. For simplicity, and because usually you only set
these attributes, this page only describes the setter version
of each attribute method.
self[format, key] = value -> self
Define a format-specific option. An alternative to define, below. Use this method to set options for reading or writing certain image formats. ImageMagick and GraphicsMagick support different options, and the list of supported options changes from release to release. For a list of the valid image formats, keys, and values, refer to the documentation for the -define option for the specific release of the library you're using.
to_s. Use
nil to set the key to a null value.self
self["tiff", "bits-per-sample"] = 2
SetImageOption (ImageMagick 6.0.0), AddDefinitions (GraphicsMagick 1.1)
self[format, key] -> value
Returns the value of the specified option for the specified format.
The value of the option. Always a string.
self["tiff", "bits-per-sample"] » 2
GetImageOption (ImageMagick 6.0.0), AccessDefinitions (GraphicsMagick 1.1)
self.channel([channel [, channel...]])
Restrict the method to the specified channel(s). This attribute is set-only.
The arguments may be any ChannelType values.
If you call channel with no arguments,
all channels are included. If you do not call
channel at all, the channels used do not include
the alpha channel.
self.define(format, key[, value])
Define a format-specific option. See []=, above.
to_s. If
omitted, the key is simply defined to an null value.self
self.define("tiff", "bits-per-sample", 2)
SetImageOption (ImageMagick 6.0.0), AddDefinitions (GraphicsMagick 1.1)
self.undefine(format, key)
Delete an option definition set by []=
or define. This is not the same as
setting the option to a null value. The undefine
method removes the option name from the list of options for the
specified format.
self
self.undefine("tiff", "bits-per-sample")
self.antialias= true or false
Control antialiasing of rendered
Postscript and Postscript or TrueType fonts. The default
is true.
self.authenticate= aString
Decrypt an image with this password.
This attribute can be used to specify the password to be used when reading an image or image sequence that is in an encrypted format, such as PDF.
self.background_color= aString or aPixel
Set the image background color. The default is "white".
A color name or a aPixel.
self.border_color= aString or aPixel
Set the image border color. The default is "#dfdfdf".
A color name or a aPixel.
self.colorspace= aColorspaceType
self.comment= aString
Use this option to assign a specific comment to the image, when writing to an image format that supports comments.
You can include the image filename, type, width, height, or other image attribute by embedding special format characters listed under the annotate method.
self.compression= aCompressionType
Specify the type of compression used when writing the image. Only some image formats support compression. For those that do, only some compression types are supported. If you specify an compression type that is not supported, the default compression type (usually NoCompression) is used instead.
Some compression types support varying levels of
compression. See the quality attribute.
The following table shows the image formats that support compression. For each format, the right-hand column shows the supported compression types. The default compression type is shown in bold.
| Format | Compression Types |
|---|---|
| BMP | NoCompression, RLECompression |
| DIB | NoCompression, RLECompression |
| FPX | NoCompression, JPEGCompression |
| GIF | LZWCompression (see Notes, below) |
| JNG | NoCompression, JPEGCompression |
| JP2 | JPEGCompression, LosslessJPEGCompression |
| JPG | JPEGCompression, LosslessJPEGCompression |
| MIFF | NoCompression, RLECompression |
| MNG | NoCompression, JPEGCompression |
| PALM | NoCompression, FaxCompression, RLECompression |
| PDB | NoCompression, RLECompression |
| NoCompression, JPEGCompression, LZWCompression, ZipCompression | |
| PICT | NoCompression, JPEGCompression |
| PNG | NoCompression, ZIPCompression |
| PS | NoCompression, RLECompression |
| PS2 | RLECompression, FaxCompression, JPEGCompression, LZWCompression, NoCompression |
| PS3 | FaxCompression, JPEGCompression, LZWCompression, NoCompression, RLECompression, ZipCompression |
| TIFF | NoCompression, FaxCompression, Group4Compression, JPEGCompression, LZWCompression, RLECompression, ZipCompression |
self.density= aString or aGeometry
Specify the vertical and horizontal resolution in pixels. The default density is "72.0x72.0". This attribute can be used when writing JBIG, PCL, PS, PS2, and PS3 format images.
This attribute can also be used to specify the width and height of HISTOGRAM format images. For HISTOGRAM, the default is 256x200.
The argument can be either a string in the form "XxY" where
"X" is the horizontal resolution and "Y" is the vertical
resolution, or a Geometry
object where width is the horizontal resolution
and height is the vertical resolution.
self.delay= anInteger
This attribute is useful for regulating the animation of image sequences. delay/100 seconds must expire before the display of the next image. The default is no delay between each showing of the image sequence. The maximum delay is 65535.
self.depth= aNumber
Specify the image depth.
Either 8, 16, or 32. You can specify 16 and 32 only when ×Magick was compiled with a QuantumDepth that allows these depth values.
Use depth to specify the depth of CMYK, GRAY,
RGB, RGBA, MAP, and XC format images. See also size.
self.dispose= aDisposeType
The argument indicates the way in which the graphic is to be treated after being displayed.
A DisposeType constant.
self.dither= true or false
This attribute can be used when writing GIF images.
Apply Floyd/Steinberg error diffusion to the image. The basic strategy of dithering is to trade intensity resolution for spatial resolution by averaging the intensities of several neighboring pixels. Images which suffer from severe contouring when reducing colors can be improved with this option.
self.extract= aString or aGeometry
Specify a portion of an image to be extracted when the image is constituted. This attribute can be used to identify a subset of an image that is otherwise too large to keep in memory.
Either a geometry string or a Geometry object. For example:
self.extract = "200x200+100+100".
self.filename= aString
See capture.
self.fill= aString or aPixel
In the Image::Info class, the fill
attribute specifies the fill color to use when creating an
image with the "caption:" format..
A color name or a aPixel.
self.font= aString
Set the text rendering font.
self.format= aString
self.fuzz= aNumeric or aString
Set the level of "fuzziness" for comparing pixels. By
default the pixels must be identical to be considered equal.
The larger the fuzz value the more difference is
tolerated. See Image#fuzz.
The argument may be a numeric value or a string in the form
"NN%". In the second case, the argument is computed as a
percentage of MaxRGB. For
example, a value of '5%' sets fuzz to
0.05*MaxRGB.
self.gravity= aGravityType
The direction text gravitates to when annotating the image.
The direction you choose specifies where to
position the text when annotating the image. For example, a
gravity of CenterGravity forces the text to be
centered within the image. By default, the image gravity is
NorthWestGravity.
This attribute can be used to position the text when creating an image with the "caption:" format.
A GravityType constant.
self.image_type= anImageType
The image type classification. For example, GrayscaleType. Don't confuse this attribute with the format such as "GIF" or "JPG".
An ImageType constant.
self.interlace= anInterlaceType
[S]pecify the type of interlacing scheme for raw image formats such as RGB or YUV. NoInterlace means do not interlace, LineInterlace uses scanline interlacing, and PlaneInterlace uses plane interlacing. PartitionInterlace is like PlaneInterlace except the different planes are saved to individual files (e.g. image.R, image.G, and image.B). Use LineInterlace or PlaneInterlace to create an interlaced GIF or progressive JPEG image. The default is NoInterlace.
An InterlaceType constant.
self.label= aString
Use this option to assign a specific label to the image, when writing to an image format that supports labels, such as TIFF, PNG, MIFF, or PostScript. You can include the the image filename, type, width, height, or other image attribute by embedding special format characters. See annotate for details.
self.matte_color= aString or aPixel
Set the image transparent color. The default is "#bdbdbd".
A color name or a aPixel.
self.monitor= aProc
Set a Proc object as a progress monitor. This
proc can be used to monitor the progress of methods that accept
optional arguments such as read and
write. To stop monitoring, set the monitor to
nil. See Image#monitor for more information
about the proc. This attribute is set-only.
If you assign a monitor to an image with
self.monitor= when the image is created, the image
object inherits the monitor. Any methods applied to the new
image will be monitored as well.
Available in ImageMagick 6.1.0 and later. This method
supercedes the Magick.set_monitor method.
self.monochrome= true or false
Transform the image to black and white on input. Only the EPT, PDF, and PS formats respect this attribute.
self.orientation=anOrientationType
self.origin=aString or aGeometry
Set the image origin.
A geometry string of the
form +x+y (a "-" may be used instead of "+" to
indicate a negative offset) or a Geometry object.
self.page= aString or aGeometry
Set the equivalent size of the Postscript page. The default is "612x792>".
A geometry string or a Geometry object.
self.pointsize= aNumeric
Set the font size in points. Useful when creating "caption:" format images, for example.
self.quality= anInteger
The compression level for JPEG, MPEG, JPEG-2000, MIFF, MNG, and PNG image format. Corresponds to ×Magick's -quality option. The default is 75. See Compressing image files.
self.sampling_factor= aString
sampling factors used by JPEG or MPEG-2 encoder and YUV decoder/encoder.
This attribute specifies the sampling factors to be used by the JPEG encoder for chroma downsampling. If this attribute is omitted, the JPEG library will use its own default values. When reading or writing the YUV format and when writing the M2V (MPEG-2) format, use sampling-factor="2x1" to specify the 4:2:2 downsampling method.
A string in the form "horizontal-factorxvertical-factor"
self.server_name= aString
Set the X11 display to obtain fonts from.
self.size= aString or aGeometry
Set the width and height of the image when reading a built-in image format that does not have an inherent size, or when reading an image from a multi-resolution file format such as Photo CD, JBIG, or JPEG.
Use size to specify the width and height of
images in the CMYK, DIB, EMF, GRAY, RGB, RGBA, UYVY, YUV, or XC
formats, the width and height of some built in formats, or the
subimage size of PTIF-format images.
A geometry string or a Geometry object.
self.texture= image
Set a texture to tile onto the image background. Corresponds to the -texture option to ×Magick's convert and mogrify commands. This attribute is set-only.
An image
self.units= aResolutionType
self.view= aString
FlashPix viewing parameters.