Java Doc for IndexColorModel.java in  » 6.0-JDK-Core » AWT » java » awt » image » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Some constructors provide a means to specify an alpha component for each pixel in the colormap, while others either provide no such means or, in some cases, a flag to indicate whether the colormap data contains alpha values. If no alpha is supplied to the constructor, an opaque alpha component (alpha = 1.0) is assumed for each entry. An optional transparent pixel value can be supplied that indicates a pixel to be made completely transparent, regardless of any alpha component supplied or assumed for that pixel value. Note that the color components in the colormap of an IndexColorModel objects are never pre-multiplied with the alpha components.

The transparency of an IndexColorModel object is determined by examining the alpha components of the colors in the colormap and choosing the most specific value after considering the optional alpha values and any transparent index specified. The transparency value is Transparency.OPAQUE only if all valid colors in the colormap are opaque and there is no valid transparent pixel. If all valid colors in the colormap are either completely opaque (alpha = 1.0) or completely transparent (alpha = 0.0), which typically occurs when a valid transparent pixel is specified, the value is Transparency.BITMASK. Otherwise, the value is Transparency.TRANSLUCENT, indicating that some valid color has an alpha component that is neither completely transparent nor completely opaque (0.0 < alpha < 1.0).

If an IndexColorModel object has a transparency value of Transparency.OPAQUE, then the hasAlpha and getNumComponents methods (both inherited from ColorModel) return false and 3, respectively. For any other transparency value, hasAlpha returns true and getNumComponents returns 4.

The values used to index into the colormap are taken from the least significant n bits of pixel representations where n is based on the pixel size specified in the constructor. For pixel sizes smaller than 8 bits, n is rounded up to a power of two (3 becomes 4 and 5,6,7 become 8). For pixel sizes between 8 and 16 bits, n is equal to the pixel size. Pixel sizes larger than 16 bits are not supported by this class. Higher order bits beyond n are ignored in pixel representations. Index values greater than or equal to the map size, but less than 2ⁿ, are undefined and return 0 for all color and alpha components.

For those methods that use a primitive array pixel representation of type transferType, the array length is always one. The transfer types supported are DataBuffer.TYPE_BYTE and DataBuffer.TYPE_USHORT. A single int pixel representation is valid for all objects of this class, since it is always possible to represent pixel values used with this class in a single int. Therefore, methods that use this representation do not throw an IllegalArgumentException due to an invalid pixel value.

Many of the methods in this class are final. The reason for this is that the underlying native graphics code makes assumptions about the layout and operation of this class and those assumptions are reflected in the implementations of the methods here that are marked final. You can subclass this class for other reasons, but you cannot override or modify the behaviour of those methods.
See Also:   ColorModel
See Also:   ColorSpace
See Also:   DataBuffer
version:
   10 Feb 1997

Since IndexColorModel can be subclassed, any subclass that supports greater than 16 bits per pixel must override this method.
Parameters:
  w - the width to apply to the new WritableRaster
Parameters:
  h - the height to apply to the new WritableRaster a WritableRaster object with the specifiedwidth and height.
throws:
  UnsupportedOperationException - if the number of bits in apixel is greater than 16
See Also:   WritableRaster
See Also:   SampleModel

Since IndexColorModel can be subclassed, subclasses inherit the implementation of this method and if they don't override it then they throw an exception if they use an unsupported transferType.
Parameters:
  pixel - the specified pixel
Parameters:
  components - an array that receives the color and alpha components of the specified pixel
Parameters:
  offset - the index into the components array atwhich to begin storing the color and alpha components of thespecified pixel an array containing the color and alpha components of thespecified pixel starting at the specified offset.
throws:
  ArrayIndexOutOfBoundsException - if pixelis not large enough to hold a pixel value for thisColorModel or if the components array is not null and is not large enough to hold all the color and alpha components starting at offset
throws:
  ClassCastException - if pixel is not a primitive array of type transferType
throws:
  UnsupportedOperationException - if transferTypeis not one of the supported transer types
See Also:   ColorModel.hasAlpha
See Also:   ColorModel.getNumComponents

Since IndexColorModel can be subclassed, subclasses inherit the implementation of this method and if they don't override it then they throw an exception if they use an unsupported transferType.
Parameters:
  rgb - the integer pixel representation in the default RGBcolor model
Parameters:
  pixel - the specified pixel an array representation of the specified pixel in thisIndexColorModel.
throws:
  ClassCastException - if pixelis not a primitive array of type transferType
throws:
  ArrayIndexOutOfBoundsException - ifpixel is not large enough to hold a pixel valuefor this ColorModel
throws:
  UnsupportedOperationException - if transferTypeis invalid
See Also:   WritableRaster.setDataElements
See Also:   SampleModel.setDataElements

Since IndexColorModel can be subclassed, subclasses inherit the implementation of this method and if they don't override it then they throw an exception if they use an unsupported transferType
Parameters:
  components - an array of unnormalized color and alphacomponents
Parameters:
  offset - the index into components at which tobegin retrieving color and alpha components
Parameters:
  pixel - the Object representing an array of colorand alpha components an Object representing an array of color andalpha components.
throws:
  ClassCastException - if pixelis not a primitive array of type transferType
throws:
  ArrayIndexOutOfBoundsException - if pixel is not large enough to hold a pixel valuefor this ColorModel or the componentsarray is not large enough to hold all of the color and alphacomponents starting at offset
throws:
  UnsupportedOperationException - if transferTypeis not one of the supported transer types
See Also:   WritableRaster.setDataElements
See Also:   SampleModel.setDataElements