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

# Constants

### Miscellaneous constants

Long_version
  An extended form of the `Version` constant with the format shown here:
  `This is RMagick 1.4.0 ($Date: 2005/09/26 23:35:06 $) Copyright (C) 2005 by Timothy P. Hunter
  Built with ImageMagick 6.0.0 02/25/04 Q8 http://www.imagemagick.org
  Built for ruby 1.8.1 (2003-12-25) [i686-linux]
  Web page: http://rmagick.rubyforge.org
  Email: rmagick@rubyforge.org`
MagickVersion
  The ×Magick version string. This has the form:
  `@(#)ImageMagick X.Y.Z MM/DD/YY Q:16 http://www.imagemagick.org`
  or
  `GraphicsMagick 1.0 05/05/03 Q8 http://www.GraphicsMagick.org/`
MaxRGB
  The maximum value of a Quantum. A quantum is one of the red, green, blue, or opacity elements of a pixel in the RGB colorspace, or cyan, yellow, magenta, or black elements in the CYMK colorspace.
QuantumDepth
  The number of bits in a quantum. The relationship between QuantumDepth and MaxRGB is summarized in this table.

  How MaxRGB and QuantumDepth are related
  QuantumDepth | MaxRGB
  --- | ---
  8 | 255
  16 | 65535
  32 | 4294967295

Version
  The RMagick version string. This has the form:
  `RMagick major.minor.teeny`

### AlignType

Specify text alignment. See align=, text_align.

UndefinedAlign
LeftAlign
CenterAlign
RightAlign

### ChannelType

Specify an image channel. See channel.

UndefinedChannel
RedChannel
GreenChannel
BlueChannel
CyanChannel
MagentaChannel
YellowChannel
BlackChannel
OpacityChannel
AllChannels
GrayChannel

### ClassType

Specify the image storage class. See class_type.

UndefinedClass
  No storage class has been specified.
DirectClass
  Image is composed of pixels which represent literal color values.
PseudoClass
  Image is composed of pixels which specify an index in a color palette.

### ColorspaceType

Specify the colorspace that quantization (color reduction and mapping) is done under or to specify the colorspace when encoding an output image. Colorspaces are ways of describing colors to fit the requirements of a particular application (e.g. Television, offset printing, color monitors). Color reduction, by default, takes place in the RGBColorspace. Empirical evidence suggests that distances in color spaces such as YUVColorspace or YIQColorspace correspond to perceptual color differences more closely than do distances in RGB space. These color spaces may give better results when color reducing an image.

When encoding an output image, the colorspaces RGBColorspace, CMYKColorspace, and GRAYColorspace may be specified. The CMYKColorspace option is only applicable when writing TIFF, JPEG, and Adobe Photoshop bitmap (PSD) files. See colorspace.

UndefinedColorspace
  No colorspace has been specified.
RGBColorspace
  Red-Green-Blue colorspace
GRAYColorspace
TransparentColorspace
  The Transparent color space behaves uniquely in that it preserves the matte channel of the image if it exists.
OHTAColorspace
XYZColorspace
YCbCrColorspace
YIQColorspace
YPbPrColorspace
YUVColorspace
  Y-signal, U-signal, and V-signal colorspace. YUV is most widely used to encode color for use in television transmission.
CMYKColorspace
  Cyan-Magenta-Yellow-Black colorspace. CYMK is a subtractive color system used by printers and photographers for the rendering of colors with ink or emulsion, normally on a white surface.
SRGBColorspace
  In ×Magick, this constant is named sRGBColorspace, but since Ruby constants must start with an uppercase letter, I had to change it.
HSLColorspace
  Available in ImageMagick 5.5.7.
HWBColorspace
  Available in ImageMagick 5.5.7.

### ComplianceType

Specify the color standard from which color names are chosen. See to_color.

SVGCompliance
  Adhere to SVG color standard.
X11Compliance
  Adhere to X11 color standard.
XPMCompliance
  Adhere to XPM color standard.
AllCompliance
  The union of the 3 color standards.

### CompositeOperator

Select the image composition algorithm used to compose a `composite image` with a `image`. By default, each of the `composite image` pixels are replaced by the corresponding `image` tile pixel. Specify `CompositeOperator` to select a different algorithm. See composite.

UndefinedCompositeOp
  No composite operator has been specified.
OverCompositeOp
  The result is the union of the the two image shapes with `composite image` obscuring `image` in the region of overlap. The matte channel of the composite image is respected, so that if the composite pixel is part or all transparent, the corresponding image pixel will show through.
InCompositeOp
  The result is simply `composite image` cut by the shape of `image`. None of the image data of `image` is included in the result.
OutCompositeOp
  The resulting image is `composite image` with the shape of `image` cut out.
AtopCompositeOp
  The result is the same shape as `image`, with `composite image` obscuring `image` where the image shapes overlap. Note that this differs from OverCompositeOp because the portion of `composite image` outside of `image`'s shape does not appear in the result.
XorCompositeOp
  The result is the image data from both `composite image` and `image` that is outside the overlap region. The overlap region will be blank.
PlusCompositeOp
  The result is just the sum of the image data. Output values are cropped to 255 (no overflow). This operation is independent of the matte channels.
MinusCompositeOp
  The result of composite image - image, with overflow cropped to zero. The matte chanel is ignored (set to 255, full coverage).
AddCompositeOp
  The result of `composite image` + `image`, with overflow wrapping around (mod 256).
SubtractCompositeOp
  The result of `composite image` - `image`, with underflow wrapping around (mod 256). The add and subtract operators can be used to perform reversable transformations.
DifferenceCompositeOp
  The result of abs(`composite image` - `image`). This is useful for comparing two very similar images.
MultiplyCompositeOp
  Multiplies the color of each target image pixel by the color of the corresponding composite image pixel. The result color is always darker.
BumpmapCompositeOp
  The result `image` shaded by `composite image`.
ReplaceCompositeOp
  The resulting image is image replaced with composite image. Here the matte information is ignored. Available in ImageMagick 6.0.0.
CopyCompositeOp
  Replace the target image with the composite image.
CopyRedCompositeOp
  Copy the red channel from the composite image to the target image.
CopyGreenCompositeOp
  Copy the green channel from the composite image to the target image.
CopyBlueCompositeOp
  Copy the blue channel from the composite image to the target image.
CopyOpacityCompositeOp
  If the composite image's matte attribute is `true`, copy the opacity channel from the composite image to the target image. Otherwise, set the target image pixel's opacity to the intensity of the corresponding pixel in the composite image.
ClearCompositeOp
  Make the target image transparent. The composite image is ignored.
DissolveCompositeOp
DisplaceCompositeOp
  Displace target image pixels as defined by a displacement map. The amount of displacement can be controlled via the geometry attribute of the composite image. The default is "20x20".
ModulateCompositeOp
ThresholdCompositeOp
NoCompositeOp
DarkenCompositeOp
  Replace target image pixels with darker pixels from the composite image.
LightenCompositeOp
  Replace target image pixels with lighter pixels from the composite image.
HueCompositeOp
  Each pixel in the result image is the combination of the hue of the target image and the saturation and brightness of the composite image.
SaturateCompositeOp
  Each pixel in the result image is the combination of the saturation of the target image and the hue and brightness of the composite image.
ColorizeCompositeOp
  Each pixel in the result image is the combination of the brightness of the target image and the saturation and hue of the composite image. This is the opposite of LuminizeCompositeOp.
LuminizeCompositeOp
  Each pixel in the result image is the combination of the brightness of the composite image and the saturation and hue of the target image. This is the opposite of ColorizeCompositeOp.
ScreenCompositeOp
  Multiplies the inverse of each image's color information.
OverlayCompositeOp
CopyCyanCompositeOp
  Copy the cyan channel from the composite image to the target image. Available in ImageMagick 5.5.7.
CopyMagentaCompositeOp
  Copy the magenta channel from the composite image to the target image. Available in ImageMagick 5.5.7.
CopyYellowCompositeOp
  Copy the yellow channel from the composite image to the target image. Available in ImageMagick 5.5.7.
CopyBlackCompositeOp
  Copy the black channel from the composite image to the target image. Available in ImageMagick 5.5.7.
DstAtopCompositeOp
  Available in ImageMagick 6.0.0
DstCompositeOp
  Available in ImageMagick 6.0.0
DstInCompositeOp
  Available in ImageMagick 6.0.0
DstOutCompositeOp
  Available in ImageMagick 6.0.0
DstOverCompositeOp
  Available in ImageMagick 6.0.0
SrcAtopCompositeOp
  Available in ImageMagick 6.0.0
SrcCompositeOp
  Available in ImageMagick 6.0.0
SrcInCompositeOp
  Available in ImageMagick 6.0.0
SrcOutCompositeOp
  Available in ImageMagick 6.0.0
SrcOverCompositeOp
  Available in ImageMagick 6.0.0
ColorDodgeCompositeOp
  Available in ImageMagick 6.0.0
ExclusionCompositeOp
  Available in ImageMagick 6.0.0
HardLightCompositeOp
  Available in ImageMagick 6.0.0
SoftLightCompositeOp
  Available in ImageMagick 6.0.0

### CompressionType

Express the desired compression type when encoding an image. Be aware that most image types only support a sub-set of the available compression types. If the compression type specified is incompatable with the image, ×Magick selects a compression type compatable with the image type. See compression.

UndefinedCompression
  No compression type has been specified.
NoCompression
  The default for most formats.
BZipCompression
  BZip (Burrows-Wheeler block-sorting text compression algorithm and Huffman coding) as used by bzip2 utilities
FaxCompression
  CCITT Group 3 FAX compression
Group4Compression
  CCITT Group 4 FAX compression (used only for TIFF)
JPEGCompression
  JPEG compression. See The JPEG image compression FAQ.
JPEG2000Compression
  JPEG2000 compression for compressed PDF images. (Introduced in ImageMagick 6.2.2.)
LosslessJPEGCompression
  This compression format is almost never used.
LZWCompression
  Lempel-Ziv-Welch (LZW) compression
RLECompression
  See the Wikipedia page for Run-length encoding.
ZipCompression
  Lempel-Ziv compression (LZ77) as used in PKZIP and GNU gzip.

### DecorationType

Use with the decorate= method in the Draw class to specify the text decoration for the annotate method.

NoDecoration
  Don't decorate the text.
UnderlineDecoration
  Underline the text.
OverlineDecoration
  Overline the text.
LineThroughDecoration
  Draw a horizontal line through the middle of the text.

### DisposeType

The value of the dispose attribute.

UndefinedDispose
  No disposal specified.
NoneDispose
  Do not dispose between frames.
BackgroundDispose
  Overwrite the image area with the background color.
PreviousDispose
  Overwrite the image area with what was there prior to rendering the image.

### EndianType

The value of the endian attribute.

UndefinedEndian
LSBEndian
MSBEndian

### FilterTypes

Used to adjust the filter algorithm used when resizing images. Different filters experience varying degrees of success with various images and can take sigificantly different amounts of processing time. ×Magick uses the LanczosFilter by default since this filter has been shown to provide the best results for most images in a reasonable amount of time. Other filter types (e.g. TriangleFilter) may execute much faster but may show artifacts when the image is re-sized or around diagonal lines. The only way to be sure is to test the filter with sample images. See resize.

UndefinedFilter
PointFilter
BoxFilter
TriangleFilter
HermiteFilter
HanningFilter
HammingFilter
BlackmanFilter
GaussianFilter
QuadraticFilter
CubicFilter
CatromFilter
MitchellFilter
LanczosFilter
BesselFilter
SincFilter

### GravityType

Specify positioning of an object (e.g. text, image) within a bounding region (e.g. an image). Gravity provides a convenient way to locate objects irrespective of the size of the bounding region, in other words, you don't need to provide absolute coordinates in order to position an object. A common default for gravity is NorthWestGravity. See annotate and composite.

ForgetGravity
  Don't use gravity.
NorthWestGravity
  Position object at top-left of region
NorthGravity
  Postiion object at top-center of region
NorthEastGravity
  Position object at top-right of region
WestGravity
  Position object at left-center of region
CenterGravity
  Position object at center of region
EastGravity
  Position object at right-center of region
SouthWestGravity
  Position object at left-bottom of region
SouthGravity
  Position object at bottom-center of region
SouthEastGravity
  Position object at bottom-right of region

### ImageType

Indicate the type classification of the image. See image_type and image_type=.

UndefinedType
  No type has been specified.
BilevelType
  Monochrome image
GrayscaleType
  Grayscale image
PaletteType
  Indexed color (palette) image
PaletteMatteType
  Indexed color (palette) image with opacity
TrueColorType
  Truecolor image
TrueColorMatteTypeType
  Truecolor image with opacity
ColorSeparationType
  Cyan/Yellow/Magenta/Black (CYMK) image
ColorSeparationMatteType
OptimizeType

### InterlaceType

Specify the ordering of the red, green, and blue pixel information in the image. Interlacing is usually used to make image information available to the user faster by taking advantage of the space vs time tradeoff. For example, interlacing allows images on the Web to be recognizable sooner and satellite images to accumulate/render with image resolution increasing over time. Use `LineInterlace` or `PlaneInterlace` to create an interlaced GIF or progressive JPEG image. See interlace.

UndefinedInterlace
  No interlace type has been specified.
NoInterlace
  Don't interlace image (RGBRGBRGBRGBRGBRGB...)
LineInterlace
  Use scanline interlacing (RRR...GGG...BBB...RRR...GGG...BBB...)
PlaneInterlace
  Use plane interlacing (RRRRRR...GGGGGG...BBBBBB...)
PartitionInterlace
  Similar to plane interlacing except that the different planes are saved to individual files (e.g. image.R, image.G, and image.B)

### MetricType

The distortion metric type. See compare_channel, distortion_channel.

MeanAbsoluteErrorMetric
MeanSquaredErrorMetric
PeakAbsoluteErrorMetric
PeakSignalToNoiseRatioMetric
RootMeanSquaredErrorMetric

### NoiseType

Select the type of noise to be added to the image. See add_noise.

UniformNoise
GaussianNoise
MultiplicativeGaussianNoise
ImpulseNoise
LaplacianNoise
PoissonNoise

### Opacity

represent the maximum and minimum levels of opacity. You can specify a partial level of opacity by choosing a number between OpaqueOpacity and TransparentOpacity. For example, 25% opacity is `abs(Magick::TransparentOpacity-Magick::OpaqueOpacity) * 0.25`

TransparentOpacity
  The minimum amount of opacity.
OpaqueOpacity
  The maximum amount of opacity.

### PaintMethod

Specify how pixel colors are to be replaced in the image. See matte_floodfill and texture_floodfill.

PointMethod
  Replace pixel color at point.
ReplaceMethod
  Replace color for all image pixels matching color at point.
FloodfillMethod
  Replace color for pixels surrounding point until encountering pixel that fails to match color at point.
FillToBorderMethod
  Replace color for pixels surrounding point until encountering pixels matching border color.
ResetMethod
  Replace colors for all pixels in image with fill color.

### RenderingIntent

Rendering intent is a concept defined by ICC Spec ICC.1:1998-09, "File Format for Color Profiles". ImageMagick uses RenderingIntent in order to support ICC Color Profiles.

From the specification: "Rendering intent specifies the style of reproduction to be used during the evaluation of this profile in a sequence of profiles. It applies specifically to that profile in the sequence and not to the entire sequence. Typically, the user or application will set the rendering intent dynamically at runtime or embedding time."

See rendering_intent.

UndefinedIntent
  No intent has been specified.
SaturationIntent
  A rendering intent that specifies the saturation of the pixels in the image is preserved perhaps at the expense of accuracy in hue and lightness.
PerceptualIntent
  A rendering intent that specifies the full gamut of the image is compressed or expanded to fill the gamut of the destination device. Gray balance is preserved but colorimetric accuracy might not be preserved.
AbsoluteIntent
  Absolute colorimetric
RelativeIntent
  Relative colorimetric

### ResolutionType

By default, ImageMagick defines resolutions in pixels per inch. ResolutionType provides a means to adjust this. See units.

UndefinedResolution
  No resolution has been specified.
PixelsPerInchResolution
  Density specifications are specified in units of pixels per inch (english units).
PixelsPerCentimeterResolution
  Density specifications are specified in units of pixels per centimeter (metric units).

### StretchType

See font_stretch=.

NormalStretch
UltraCondensedStretch
ExtraCondensedStretch
CondensedStretch
SemiCondensedStretch
SemiExpandedStretch
ExpandedStretch
ExtraExpandedStretch
UltraExpandedStretch
AnyStretch

### StyleType

See font_style=.

NormalStyle
ItalicStyle
ObliqueStyle
AnyStyle

### WeightType

The font weight can be specified as one of 100, 200, 300, 400, 500, 600, 700, 800, or 900, or one of the following constants. See font_weight=.

AnyWeight
  No weight specfied.
NormalWeight
  Equivalent to 400
BoldWeight
  Equivalent to 700
BolderWeight
  Increases weight by 100
LighterWeight
  Decreases weight by 100