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Home modified by StephenG

StephenG — Thu, 28 Nov 2013 15:30:35 -0000

--- v2
+++ v3
@@ -23,7 +23,7 @@
 Building JLibJPEG
 ------------------

-To build JLibJPEG you first need to compile the Java file and then use that to build the C include file with javah.  Finally you compile the C file with the native code.  THis is an example from teh developer's own system :
+To build JLibJPEG you first need to compile the Java file and then use that to build the C include file with javah.  Finally you compile the C file with the native code.  This is an example from the developer's own system :

 ~~~~~~
 javac JLibJPEG.java
@@ -38,7 +38,20 @@

 The resulting JAR and shared library files need to be on your application's classpath to use them, of course.

-A test file is also available 
+A test java file is also available 
+
+
+Under The Hood
+---------------
+
+JLibJPEG uses standard Java and C calls and invokes only one library - libjpeg.  That's a standard library on Linux systems and available for most systems, including MS Windows.  Most systems use the libjpeg-turbo fork in practice.
+
+JLibJPEG exploits the fact that both libjpeg and Java's BUfferedImage class support the image format 3BYTE_BGR ( i.e. each pixel being three bytes in the order Blue, Green, Red ).  Of course monochrome images are just bytes and this is also supported by BufferedImage.
+
+The C code allows direct access to the libjpeg decoder.
+
+Note that the Java VM has one frustration that cannot easily be avoided.  To pass the decoded JPEG data to Java we must use a byte array.  To safely allocate this and not risk issues with the JVM we unfortunately need to allocate the byte array through Java and Java will always ( and unavoidably ) zero every single byte when we allocate.  There is no safe way around this ( although there is at least one very unsafe way around it ).  This means that we're first zeroing every byte in our multi-megapixel image array and immediately writing over all those zeros when we decode the JPEG.  Unless the Java VM is extended to add support for non-zering allocations at some point in the future, we're stuck with this waste of time.  Despite this, JLibJPEG can still provide a considerable increase in load times, especially when coupled with libjpeg-turbo ( the Linux default ).
+

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Home modified by StephenG

StephenG — Thu, 28 Nov 2013 15:13:03 -0000

--- v1
+++ v2
@@ -1,8 +1,44 @@
-Welcome to your wiki!
+JLibJPEG is a small Java class interfacing to C code using JNI.  Ut is designed to load large JPEGs as quickly as possible.

-This is the default page, edit it as you see fit. To add a new page simply reference it within brackets, e.g.: [SamplePage].
+JPEG images are a major, perhaps *the* major, image file type used in applications.  Java's standard methods for loadig a JPEG to a BufferedImage are very slow.  This is particularl;y frsutrating if you want to develop applications that view the large image files from modern cameras.  JLibJPEG tries to address this by providing an explicit call to load JPEGs.

-The wiki uses [Markdown](/p/jlibjpeg/wiki/markdown_syntax/) syntax.
+JLibJPEG should work with both RGB and B&W images - it has been tested with both.
+
+Performance tests on the developer's system using an AMD A8 APU indicate a speedup of up to a factor of ten over ImageIO for a 16Mp JPEG straight from a digital camera.  The smaller the image, the less the gain.  In practical terms this made the difference between a photo viewer application that could flip between images ona key stroke and one that had serious lag when images were switched.
+
+
+Using JLibJPEG
+----------------
+
+Using JLIbJPEG is very simple - it's just one call to a static method.  For example ;
+
+~~~~~~
+BufferedImage bi = JLibJPEG.loadImage( "location/name.jpg" ) ;
+~~~~~~
+
+
+The loadImage() method returns *null* if the load operation fails for any reason.  **No** exceptions should be thrown.
+
+
+Building JLibJPEG
+------------------
+
+To build JLibJPEG you first need to compile the Java file and then use that to build the C include file with javah.  Finally you compile the C file with the native code.  THis is an example from teh developer's own system :
+
+~~~~~~
+javac JLibJPEG.java
+
+javah -jni JLibJPEG
+
+jar cf JLibJPEG.jar *.class
+
+gcc -g -shared -fPIC -I/usr/lib/jvm/java-7-openjdk-amd64/include -o libJLibJPEG.so JLibJPEG.c -ljpeg
+~~~~~~
+
+
+The resulting JAR and shared library files need to be on your application's classpath to use them, of course.
+
+A test file is also available 

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Home modified by StephenG

StephenG — Wed, 27 Nov 2013 12:25:06 -0000

Welcome to your wiki!

This is the default page, edit it as you see fit. To add a new page simply reference it within brackets, e.g.: [SamplePage].

The wiki uses Markdown syntax.

Project Members:

StephenG (admin)