Images In JavaPaul Cockshott

ALMA TADEMA RIVALES INCONSCIENTES 1893

Introduction

• The AWT and how to put a simple image onto the screen

• Layout managers• The Jimage Class,

Summary of this section

• At the end of this lecture you should have an idea of how to display a JPEG image on the screen, and how to load it into the Jimage class to carry out further image processing.

Agenda

• AWT Images• Image Producers and Consumers• Jimage class• Pixel Representations• JPEG files

Overview

• AWT abstract windows toolkit, supported by JavaSoft

• Operating system independent layer for windowing in Java

• Fiendishly obscure• Designed around requirements of images

being streamed off the web

Connections

• Simple image display program to show how to display a JPEG file

• Pipeline model of image production• Jimages act as image consumers• Jimages allow arithmetic on image• Jimages provide output to AWT images

and JPEG

How to display a picture 1

import java.awt.*;

import java.awt.image.*;

import java.util.*;

class JPEGshow extends Frame {

...

static public void main(String[] args) {

if (args.length == 1) new JPEGshow(args[0]);

else System.err.println("usage: java JPEGshow <image file>");

}

}

This is a standard Java Program class with a public static void main method

Constructor for JPEGshow

JPEGshow(String filename) {

super("JPEG show Example");

add(

new ImageCanvas(getToolkit().getImage(filename) ),

BorderLayout.CENTER);

setSize(700, 540);

show();

}

See slide on these

Read in a JPEG file

Size of a frame

The toolkit

• Each frame has associated with it a toolkit object the provides an interface to OS specific operations.

• CreateImage

• CreateMenu

• CreateLabel

• CreateMenuBar …. etc

Roll your own ImageCanvas

class ImageCanvas extends Component {

Image image;

ImageCanvas(Image image)

{this.image = image;}

public void paint(Graphics g)

{ g.drawImage(image, 0, 0, this);}

}

Paint is called whenever a component must be shown,the Graphics object does the actual drawing, it has to bepassed in because it is what knows about physicallydrawing on the screen

Constructor just stores the image

Image Class

• Pipeline flow model of image processing• Images are just tokens linking producers and

consumers

ImageImageProducer ImageConsumer

ImageProducer Methods

• addConsumer(ImageConsumer ic) This method is used to register an ImageConsumer with the ImageProducer for access to the image data during a later reconstruction of the Image.

• removeConsumer(ImageConsumer ic) This method removes the given ImageConsumer object from the list of consumers currently registered to receive image data.

• startProduction(ImageConsumer ic) This method starts an immediate reconstruction of the image data

ImageConsumer methods

•  void setDimensions(int width, int height)

 The dimensions of the source image are reported using the setDimensions method call.

•  Void setPixels(int x, int y, int w, int h, ColorModel model, byte[] pixels, int off, int scansize)

The pixels of the image are delivered using one or more calls to the setPixels method.

Image Class continued

ImageImageProducer ImageConsumer

Images contain a pointer to their producer which holds the actualdata for the image. This can be recovered using the getSource method. This allows a consumer to get at the pixel data ofan image by adding itself to the producer and starting production

Image.getSource

Summary

• AWT is operating system independent• Streaming image model• Images as tokens• Producer - consumer pipeline• See chapters 6 of textbook

Buffered Image Class

• Standard AWT images are just tokens for data streams.

• A BufferedImage actually contains the data.

Colour model Raster

BufferedImage

JPEGCodec class

• This class has factory methods to create JPEG encoders and decoders:

• createJPEGDecoder(InputStream s)• createJPEGEncoder(OutputStream d)

Read a BufferedImage

FileInputStream in = new FileInputStream(“myfile.jpg”);

JPEGImageDecoder dec= JPEGCodec.createJPEGDecoder(in);

BufferedImage im = decoder.decodeAsBufferedImage();

getRGB

• You can access the pixels of a buffered image using

int getRGB(int x, int y)The default colour representation is:

alpha red green blue

Bit 0Bit 31

Writing pixels

• This can be done with the setRGB method.

• This takes x, and y co-ordinates and a pixel encoded as a 32 bit integer

• im . setRGB(2, 5, 255);• Would set pixel 2,5 to 255 = bright blue.

Creating sub images

• You can create a sub area within a buffered image using the

• public BufferedImage getSubimage(– int x, – int y,– int w,– int h);

Method of BufferedImage

Jimage implements ImageConsumer

• Library of image processing classes developed in the department

• Available for student practicals• Algebraic rather than stream oriented• Interfaces to MMX hardware under

windows

Algebraic orientation

By this we mean the it is structured around algebraic expressions whose values are images

Thus if and are images and is some operator then

is also an image

Jimage operators

• Arithmetic J Universal plus(Universal)

• I-JUniversal minus(Universal)• I×JUniversal times(Universal)• I÷JUniversal divide(Universal) IUniversal abs()• Filtering• Jimage convolve(double[] k) convolve with symmetrical separable

kernel.• public abstract Jimage convolve(double[][] kernel)with non

separable kernel

Scaling

• Jimage getScaledInstance(int nwidth, int nheight) This scales with bicubic interpolation.

• Jimage getScaledInstance(int nwidth, int nheight, int ndepth) This method allows the depth as well as area of an image to be altered if it is reduced the planes are aggregated if increased they are interpolated.

More operations

Data accessint rgbpixel(int x,int y)

Converts the plane information into a pixel in the direct color model of java.

public abstract int upixel(int x, int y, int plane) - returns unsigned integer pixelpublic abstract float fpixel(int x, int y, int plane)

Returns the pixel in the range -1 to +1.

Data Access

• public abstract void setPixel(int x,• int y,• int plane,• double pix)

– Pixel information in range -1 to +1• public void setSubImage(int x,• int y,• int z,• Jimage im)

– Update an area of an image with another one. The other one must not run off the edge of the one being written to. The source of the copying is the 0th plane of the source jimage.

Jimage input output

• public void putJPEGImage(• java.lang.String fileName,• int quality)• throws java.io.IOException

– Outputs the image to a jpeg file• public boolean getImage(java.lang.String

fileName)– Initialise the Jimage from the specified file. The file

must be jpeg or gif.

Jimage to AWT Image conversion

• public java.awt.Image getAWTImage()

• public java.awt.image.ImageProducer getProducer()

Jimage implementations

J IM A G E C L A S S H IE R A R C H Y

In te lB Im ageR u n s b e st o n M M X

W ind ow s o n ly

C O M .C 3 D .IM A G EB yte Im age

G e ne ric Ja va

In te lIm ageR u n s b e st o n M M X

W ind o w s O n ly

C O M .C 3 D .IM A G ES ho r tIm a ge

G e ne ric Ja va

In te lF Im a geR u ns be s t o n P III

W ind o w s O n ly

C O M .C 3 D .IM A G EF loa tIm age

G e ne ric Ja va

C O M .C 3 D .IM A G EJ im a gea b s tra ct

An example program

• class Jimageshow extends Frame {• Jimageshow(String filename) {• super("Jimage show Example");• Jimage raw=new ByteImage(100,200,3);• if (raw.getImage(filename)){• Jimage cooked = (Jimage)raw.times(0.3);• add(new ImageCanvas(cooked.getAWTImage()),

BorderLayout.CENTER);• setSize(700, 540);• show();• }• }

Create Jimage with byte pixels

Multiply by 0.3

Convert to AWTfor display

Pixel Representations

When dealing with displays it is conventional to assume that pixels are bytes holding numbers in the range 0 to 255.

0 Is assumed to be black

1 Is assumed to be white or maximum brightness of any given colour.

For multicolour displays with 3 colour components, the convention is to have 3 fields of range 0..255 to hold the colour information.

Pixel Representations AWT

For multicolour displays with 3 colour components, the convention is to have 3 fields of range 0..255 to hold the colour information. The AWT does this with the class Color.

• public Color(int rgb)– Creates a color with the specified RGB value, where the

red component is in bits 16-23 of the argument, the green component is in bits 8-15 of the argument, and the blue component is in bits 0-7. The value zero indicates no contribution from the primary color component.

– A Jimage returns this format with int rgbpixel().

Pixel Representations: Bytes

The byte data type in Java does not take on the values 0..255. Instead it takes on the values -128 to 127.

There are no unsigned bytes in Java.

This creates a problem for the representation of pixels in Jimages.

The solution adopted is to adopt the following representation

• -128 = black

• 0 = mid grey

• 127 = white

Pixel Representations: Floats

If byte pixels are signed then so must other representations be.

The solution adopted is to adopt the following representation for floats

• -1 = black

• 0 = mid grey

• 1 = white

Conversions between representations

unsigned bytes shorts float min value 0 -128 -2048 -1

maxval 255 127 2047 1

medianval 127.5 -0.5 -0.5 0

range 255 255 4095 2

As shown in table a pixel in representationis converted to a pixel in representation by the operation:

Signed Pixels : advantages

Signed pixels seem at first to be counter-intuitive but they have numerous advantages.

• A value of 0 or mid grey can be viewed as the ‘most likely’ value that a pixel takes on in the absence of other information.

• If you do arithmetic on images, in particular subtract one image from another, then negative values of pixels naturally arise.

• Signed pixels allow straightforward implementation of contrast adjustments. For instance multiplying an image by 0.5 halves the contrast in the image.

Signed Pixels : contrast adjustment

Signed pixels allow straightforward implementation of contrast adjustments. For instance multiplying an image by 0.5 halves the contrast in the image.

0.5

1

-1

0.5

Initial contrast rangeFinalcontrastrange

0.5

-0.5

0.25

-0.25

Image Multiplication

Image Addition

Image subtraction

What Is Convolution

• Convolution takes a kernel of coefficients and multiplies each pixel in a neighbourhood by the corresponding coefficient, and then sums the result

x y p[I+x, j+y]*k[x,y]

• Will give the convolved pixel at position i, j

1 D convolution

• A 1 D convolution takes a one dimensional array as a kernel and applies it first in the X and then in Y dimension.

• This can often be performed faster than a 2d convolution

Image Convolution: smoothing

double[] k= {0.1,0.1,0.2,0.2,0.2,0.1,0.1};

marble.convolve(k)=

marble =

Note sum ofcoefficients =1

Image Convolution: sharpening

double[] k= {-0.3,1.6,-0.3}

marble.convolve(k)=

marble =

Note sum ofcoefficients =1number terms is odd

Convolution in Java2D

• Java 2D provides a standard library for convolution of buffered images

• This uses the class Kernel and ConvolveOp

Kernels in JAVA 2D

float[] blur={ 0.0f, 0.1f, 0.0f, 0.1f, 0.6f, 0.1f,

0.0f, 0.1f, 0.1f};

Kernel k= new Kernel(3,3, blur);

im = new ConvolveOp(K).filter(im,null);

This will blur the image im by applying the 3 by 3 kernel blur to it.

Importance of speed

• Image may contain a million pixels, • Arithmetic may be required on each one• Important to optimise operations or they

are very time consuming• May need to use assembler kernels• May need to use special purpose

instructions

Multimedia Extensions MMX

• Intel and other CPU manufacturers have been adding to the instruction sets of their computers new extensions that handle multi-media data.

• The aim is to allow operations to proceed on multiple pixels each clock cycle

MMX 2

• Standard Intel register set

eaxebxecxedxespebpesiedi

8 General Registers 8 floating point registers

32 bit 64 bit

fp0fp1fp2fp3fp4fp5fp6fp7

MMX 3

• Standard Intel register set operating in MMX mode

eaxebxecxedxespebpesiedi

8 General Registers 8 multimedia registers

32 bit 64 bit

mm0mm1mm2mm3mm4mm5mm6mm7

MMX 4 motivation

• Existing operating systems must still work unchanged

• Applications not using MMX run unchanged

• No new state added to the CPU

Hence, shared use of the FP registers, since these are already supported by exising OS’s

MMX data formats

One 64bit integer QUADWORD

Two 32 bit integer DOUBLEWORDS

Four 16 bit WORDS

Eight 8 bit BYTES

Problem of overflows

• A problem with limited precision arithmetic is that overflows frequently occur. This can give rise to meaningless results: consider

• 200+175 = 375 but in 8 bit binary

11001000

+10101111

=101110111Leading 1 is discarded

This leaves an answer of 119 decimal – clearly wrong

Using saturation

• You can fix this by using conditionalsunsigned char p1,p2,p3;

int I3= (int)p1 + (int)p2;

p3=(I3>255?255:(unsigned char)I3);

Expansion of the code 1

12: j=(int)(*p1++)+(int)(*p2++);00401043 mov ecx,dword ptr [ebp-4]00401046 xor edx,edx00401048 mov dl,byte ptr [ecx]0040104A mov eax,dword ptr [ebp-8]0040104D xor ecx,ecx0040104F mov cl,byte ptr [eax]00401051 add edx,ecx00401053 mov dword ptr [ebp-14h],edx00401056 mov edx,dword ptr [ebp-8]00401059 add edx,10040105C mov dword ptr [ebp-8],edx0040105F mov eax,dword ptr [ebp-4]00401062 add eax,100401065 mov dword ptr [ebp-4],eax

Expansion 2

13:14: *p3 = (unsignedchar)(j>255?255:j);00401068 cmp dword ptr [ebp-14h],0FFh0040106F jle main+6Ah (0040107a)00401071 mov dword ptr [ebp-18h],0FFh00401078 jmp main+70h (00401080)0040107A mov ecx,dword ptr [ebp-14h]0040107D mov dword ptr [ebp-18h],ecx00401080 mov edx,dword ptr [ebp-0Ch]00401083 mov al,byte ptr [ebp-18h]00401086 mov byte ptr [edx],al15: p3++;00401088 mov ecx,dword ptr [ebp-0Ch]0040108B add ecx,10040108E mov dword ptr [ebp-0Ch],ecx

Total of 26 instructions in the kernel

Alternative using mmx

• Iu8vec8 *v1,*v2,*v3;• int i,j,k;• for(i=0;i<31;i++){• *v3=(*v1++)+(*v2++);• v3++;• }• _mm_empty();

Type represents 8 by 8bit integers

Arithmetic on 8 bytes at a time

Indicates MMX regs are now free

Optimised Assembler Loop

mov ecx ,32 ; load counter with 32

l1: movq mm0,[esi] ; load 8 bytes

add esi,8 ; inc src pntr

paddusb mm0,[edx] ; packed unsigned add bytes

add edx,8 ; inc src pntr

movq [edi],mm0 ; store 8 byte result

add edi,8 ; inc dest pntr

loop nz,l1 ; dec counter,

; repeat non zero

Go round only 32 times not 256

Total of 6 instructions in kernel

Speed Gain

• On image of 256x256 pixels • Old C code executes 26*256*256

instructions = 1,703,936 instructions• Optimised mmx code executes 6*256*32

instructions = 49,152• Note that no compiler currently will give

the optimised code. It has to be hand assembled.

Image Processing Library

• Intel Provide an image porcessing library that can be downloaded from their web site.

• It provides efficient access to the MMX hardware.

• It provides frequently used Image Processing Operations.

• It requires a set of DLLs in your path to run

Image Processing Library 2

At the core of IPL is the ability to write to a single API and get the best possible results for any Intel processor. The libraries have as many as six processor-specific branches for each function and six sets of carefully written assembly code, but only one entry point to each function.

Image Processing Library 3

                                                     

                           

Image Processing Library 4

• Use of Intel IPL complex and requires C• I have provided 2 java classes that call the IPL.• IntelBImage and IntelFImage. These are

documented in the Jimage web pages. They inherit from ByteImage and FloatImage

• To use them the Intel IPL must have been installed on your machine and be on the path.

• If you are forced to use Unix machines the libraries will not be available to you.

                                                     

                           

Where to get more information

• http://www.javasoft.com/products/jdk/1.2/docs/api/java/awt/package-summary.html

• http://developer.intel.com/vtune/perflibst/ipl/index.htm

• http://developer.intel.com/vtune/perflibst/ipl/ipapi.htm

Feedback

• What did you not understand here?• What would you like more information on?