Learn Java
Learn Java and other programming languages for free.
Friday, May 17, 2013
Sunday, November 18, 2012
Class AlphaComposite
java.lang.Objectjava.awt.AlphaComposite
- All Implemented Interfaces:
- Composite
The
AlphaComposite
class implements basic alpha compositing rules for combining source and destination colors to achieve blending and transparency effects with graphics and images. The specific rules implemented by this class are the basic set of 12 rules described in T. Porter and T. Duff, "Compositing Digital Images", SIGGRAPH 84, 253-259. The rest of this documentation assumes some familiarity with the definitions and concepts outlined in that paper.This class extends the standard equations defined by Porter and Duff to include one additional factor. An instance of the
AlphaComposite
class can contain an alpha value that is used to modify the opacity or coverage of every source pixel before it is used in the blending equations.It is important to note that the equations defined by the Porter and Duff paper are all defined to operate on color components that are premultiplied by their corresponding alpha components. Since the
ColorModel
and Raster
classes allow the storage of pixel data in either premultiplied or non-premultiplied form, all input data must be normalized into premultiplied form before applying the equations and all results might need to be adjusted back to the form required by the destination before the pixel values are stored.Also note that this class defines only the equations for combining color and alpha values in a purely mathematical sense. The accurate application of its equations depends on the way the data is retrieved from its sources and stored in its destinations. See Implementation Caveats for further information.
The following factors are used in the description of the blending equation in the Porter and Duff paper:
Using these factors, Porter and Duff define 12 ways of choosing the blending factors Fs and Fd to produce each of 12 desirable visual effects. The equations for determining Fsand Fd are given in the descriptions of the 12 static fields that specify visual effects. For example, the description for
Factor Definition As the alpha component of the source pixel Cs a color component of the source pixel in premultiplied form Ad the alpha component of the destination pixel Cd a color component of the destination pixel in premultiplied form Fs the fraction of the source pixel that contributes to the output Fd the fraction of the destination pixel that contributes to the output Ar the alpha component of the result Cr a color component of the result in premultiplied form
SRC_OVER
specifies that Fs = 1 and Fd = (1-As). Once a set of equations for determining the blending factors is known they can then be applied to each pixel to produce a result using the following set of equations:Fs = f(Ad) Fd = f(As) Ar = As*Fs + Ad*Fd Cr = Cs*Fs + Cd*FdThe following factors will be used to discuss our extensions to the blending equation in the Porter and Duff paper:
Factor Definition Csr one of the raw color components of the source pixel Cdr one of the raw color components of the destination pixel Aac the "extra" alpha component from the AlphaComposite instance Asr the raw alpha component of the source pixel Adr the raw alpha component of the destination pixel Adf the final alpha component stored in the destination Cdf the final raw color component stored in the destination
Preparing Inputs
TheAlphaComposite
class defines an additional alpha value that is applied to the source alpha. This value is applied as if an implicit SRC_IN rule were first applied to the source pixel against a pixel with the indicated alpha by multiplying both the raw source alpha and the raw source colors by the alpha in the AlphaComposite
. This leads to the following equation for producing the alpha used in the Porter and Duff blending equation:As = Asr * AacAll of the raw source color components need to be multiplied by the alpha in the
AlphaComposite
instance. Additionally, if the source was not in premultiplied form then the color components also need to be multiplied by the source alpha. Thus, the equation for producing the source color components for the Porter and Duff equation depends on whether the source pixels are premultiplied or not:Cs = Csr * Asr * Aac (if source is not premultiplied) Cs = Csr * Aac (if source is premultiplied)No adjustment needs to be made to the destination alpha:
Ad = AdrThe destination color components need to be adjusted only if they are not in premultiplied form:
Cd = Cdr * Ad (if destination is not premultiplied) Cd = Cdr (if destination is premultiplied)
Applying the Blending Equation
The adjusted As, Ad, Cs, and Cd are used in the standard Porter and Duff equations to calculate the blending factors Fs and Fd and then the resulting premultiplied componentsAr and Cr.Preparing Results
The results only need to be adjusted if they are to be stored back into a destination buffer that holds data that is not premultiplied, using the following equations:Adf = Ar Cdf = Cr (if dest is premultiplied) Cdf = Cr / Ar (if dest is not premultiplied)Note that since the division is undefined if the resulting alpha is zero, the division in that case is omitted to avoid the "divide by zero" and the color components are left as all zeros.
Performance Considerations
For performance reasons, it is preferrable thatRaster
objects passed to the compose
method of a CompositeContext
object created by the AlphaComposite
class have premultiplied data. If either the source Raster
or the destination Raster
is not premultiplied, however, appropriate conversions are performed before and after the compositing operation.Implementation Caveats
- Many sources, such as some of the opaque image types listed in the
BufferedImage
class, do not store alpha values for their pixels. Such sources supply an alpha of 1.0 for all of their pixels. - Many destinations also have no place to store the alpha values that result from the blending calculations performed by this class. Such destinations thus implicitly discard the resulting alpha values that this class produces. It is recommended that such destinations should treat their stored color values as non-premultiplied and divide the resulting color values by the resulting alpha value before storing the color values and discarding the alpha value.
- The accuracy of the results depends on the manner in which pixels are stored in the destination. An image format that provides at least 8 bits of storage per color and alpha component is at least adequate for use as a destination for a sequence of a few to a dozen compositing operations. An image format with fewer than 8 bits of storage per component is of limited use for just one or two compositing operations before the rounding errors dominate the results. An image format that does not separately store color components is not a good candidate for any type of translucent blending. For example,
BufferedImage.TYPE_BYTE_INDEXED
should not be used as a destination for a blending operation because every operation can introduce large errors, due to the need to choose a pixel from a limited palette to match the results of the blending equations. - Nearly all formats store pixels as discrete integers rather than the floating point values used in the reference equations above. The implementation can either scale the integer pixel values into floating point values in the range 0.0 to 1.0 or use slightly modified versions of the equations that operate entirely in the integer domain and yet produce analogous results to the reference equations.Typically the integer values are related to the floating point values in such a way that the integer 0 is equated to the floating point value 0.0 and the integer 2^n-1 (where nis the number of bits in the representation) is equated to 1.0. For 8-bit representations, this means that 0x00 represents 0.0 and 0xff represents 1.0.
- The internal implementation can approximate some of the equations and it can also eliminate some steps to avoid unnecessary operations. For example, consider a discrete integer image with non-premultiplied alpha values that uses 8 bits per component for storage. The stored values for a nearly transparent darkened red might be:
(A, R, G, B) = (0x01, 0xb0, 0x00, 0x00)
If integer math were being used and this value were being composited inSRC
mode with no extra alpha, then the math would indicate that the results were (in integer format):
(A, R, G, B) = (0x01, 0x01, 0x00, 0x00)
Note that the intermediate values, which are always in premultiplied form, would only allow the integer red component to be either 0x00 or 0x01. When we try to store this result back into a destination that is not premultiplied, dividing out the alpha will give us very few choices for the non-premultiplied red value. In this case an implementation that performs the math in integer space without shortcuts is likely to end up with the final pixel values of:
(A, R, G, B) = (0x01, 0xff, 0x00, 0x00)
(Note that 0x01 divided by 0x01 gives you 1.0, which is equivalent to the value 0xff in an 8-bit storage format.)
Alternately, an implementation that uses floating point math might produce more accurate results and end up returning to the original pixel value with little, if any, roundoff error. Or, an implementation using integer math might decide that since the equations boil down to a virtual NOP on the color values if performed in a floating point space, it can transfer the pixel untouched to the destination and avoid all the math entirely.
These implementations all attempt to honor the same equations, but use different tradeoffs of integer and floating point math and reduced or full equations. To account for such differences, it is probably best to expect only that the premultiplied form of the results to match between implementations and image formats. In this case both answers, expressed in premultiplied form would equate to:
(A, R, G, B) = (0x01, 0x01, 0x00, 0x00)
and thus they would all match.
- Because of the technique of simplifying the equations for calculation efficiency, some implementations might perform differently when encountering result alpha values of 0.0 on a non-premultiplied destination. Note that the simplification of removing the divide by alpha in the case of the SRC rule is technically not valid if the denominator (alpha) is 0. But, since the results should only be expected to be accurate when viewed in premultiplied form, a resulting alpha of 0 essentially renders the resulting color components irrelevant and so exact behavior in this case should not be expected.
Friday, November 16, 2012
california divorce lawyer
accounting software
term life
Mesothelioma Lawyers San Diego
Endowment Selling
Car free insurance online quot
Car free insurance online quot
Interface ActiveEvent
- All Known Implementing Classes:
- InvocationEvent
public interface ActiveEvent
dispatch()
method will be called when the event is dispatched, using the EventDispatchThread
.This is a very useful mechanism for avoiding deadlocks. If a thread is executing in a critical section (i.e., it has entered one or more monitors), calling other synchronized code may cause deadlocks. To avoid the potential deadlocks, an
ActiveEvent
can be created to run the second section of code at later time. If there is contention on the monitor, the second thread will simply block until the first thread has finished its work and exited its monitors.For security reasons, it is often desirable to use an
ActiveEvent
to avoid calling untrusted code from a critical thread. For instance, peer implementations can use this facility to avoid making calls into user code from a system thread. Doing so avoids potential deadlocks and denial-of-service attacks.Interface Composite
Secured Loan Calculator,Settlements.
- All Known Implementing Classes:
- AlphaComposite
public interface Composite
Composite
interface, along with CompositeContext
, defines the methods to compose a draw primitive with the underlying graphics area. After the Composite
is set in the Graphics2D
context, it combines a shape, text, or an image being rendered with the colors that have already been rendered according to pre-defined rules. The classes implementing this interface provide the rules and a method to create the context for a particular operation. CompositeContext
is an environment used by the compositing operation, which is created by the Graphics2D
prior to the start of the operation. CompositeContext
contains private information and resources needed for a compositing operation. When the CompositeContext
is no longer needed, the Graphics2D
object disposes of it in order to reclaim resources allocated for the operation.Instances of classes implementing
Composite
must be immutable because the Graphics2D
does not clone these objects when they are set as an attribute with thesetComposite
method or when the Graphics2D
object is cloned. This is to avoid undefined rendering behavior of Graphics2D
, resulting from the modification of theComposite
object after it has been set in the Graphics2D
context.Since this interface must expose the contents of pixels on the target device or image to potentially arbitrary code, the use of custom objects which implement this interface when rendering directly to a screen device is governed by the
readDisplayPixels
AWTPermission
. The permission check will occur when such a custom object is passed to thesetComposite
method of a Graphics2D
retrieved from a Component
.
Subscribe to:
Posts (Atom)