Transcript ManipulatingPictures-Ch5

Workshop for Programming And
Systems Management Teachers
Chapter 5
Manipulating Pictures, Arrays, and
Loops
Georgia Institute of Technology
Learning Goals
• Understand at a conceptual and practical
level
– How to manipulate digital images using
methods?
– What is an array?
– What is a loop?
• While and for loops
– What is a package?
– How do you import classes?
– What is a comment?
Georgia Institute of Technology
Digital Pictures
• Represented as an array of pixels
– With a red, green, and blue value stored for each
pixel
• Stored in .jpg (JPEG) files
– International standard
– With lossy compression
• Lossy means not all data is stored
– But what is lost isn’t that important
• Compression means made smaller
• Other formats for storing digital pictures are
GIFF and BMP
Georgia Institute of Technology
What is an Array?
• Storage for a
sequence of items
– Of the same type
• You can access items
by using an index
• The index starts at 0
0
1
2
3
4
5
3
7
9
2
1
5
0
1
2
3
8
3
2
6
– The first item is at
index 0
– The second item is at
index 1
– The last item is at
index (length – 1)
Georgia Institute of Technology
How do you Declare an Array?
• There are two ways
– Type[] name;
– Type name[];
• You can give values for the array when
you declare it
int[] grades = {88, 90, 75, 93, 94};
• You can also create the array when you
declare it
int[] grades = new int[5];
Georgia Institute of Technology
How do you Access Array Items?
• In Java to access an array item use
– arrayName[index]
• To set a value in an array
grades[0] = 88;
grades[1] = 90;
• To get a value from an array
int total = grades[0] + grades[1] + grades[2] +
grades[3] + grades[4];
• Arrays know their lengths
arrayName.length;
Georgia Institute of Technology
Array Exercise
• In DrJava declare and
create these two
arrays
• Check that you
created them
correctly by getting
the value at each
index
• Check the length of
the array with
3
7
9
2
8
3
2
6
arrayName.length
Georgia Institute of Technology
1
5
Manipulating a Picture
• To manipulate a picture we need to
manipulate the pixels that make up the
picture
– Change the red, green, or blue values at the
pixel
• Pixel is also a class
– Each pixel object has a red, green, and blue
value
Georgia Institute of Technology
What Data does a Picture Object Have?
• A picture object has an array of pixel
objects
– That it read from the JPEG file
• It knows it’s width
pictureObj.getWidth()
• It knows it’s height
pictureObj.getHeight()
• It knows how to return an array of pixels
Pixel[] pixels = pictureObject.getPixels()
Georgia Institute of Technology
Picture Exercise
• Create a picture in DrJava
– get the pictures width, height, and pixels
String fileName = FileChooser.pickAFile();
Picture picture = new Picture(fileName);
int width = picture.getWidth();
System.out.println(“The picture width is “ + width);
int height = picture.getHeight();
System.out.println(“The picture height is “ + height);
Pixel[] pixels = picture.getPixels();
System.out.println(pixels.length + “ pixels”);
Georgia Institute of Technology
Pixel Objects
• Each pixel has a red, green, and blue
value
– getRed(), getGreen(), getBlue()
– setRed(v), setGreen(v), setBlue(v)
• Each pixel knows the location it was in the
picture object
– getX(), get(Y)
• You can also get and set the color at the
pixel
– getColor(), setColor(color)
Georgia Institute of Technology
Pixel X and Y Values
• A picture has pixels
arranged in a grid
– The location of the pixel
along the horizontal axis
is the x value
• x starts at 0 to width - 1
– The location of the pixel
along the vertical axis is
the y value
• y starts at 0 to height - 1
Georgia Institute of Technology
Color Objects
• There is a class defined in Java that
represents color
– The Color class in the package java.awt
– To use the class you must either
• import java.awt.Color;
• Use the full name java.awt.Color
• You can create a color object by giving the
red, green, and blue values
– Color color = new Color(255,10,125);
Georgia Institute of Technology
Predefined Colors
• The Color class has
defined class constants
for many colors
– Color.red, Color.green,
Color.blue, Color.black,
Color.white, Color.yellow,
Color.gray, Color.orange,
Color.pink, Color.cyan,
Color.magenta
– Or you can use all
uppercase names
• Color.RED, Color.BLUE, …
Georgia Institute of Technology
Getting and Setting Pixel Colors
• To get a pixel’s color as a color object
– Color color = pixel.getColor();
– int red = color.getRed();
– int green = color.getGreen();
• To set a pixel’s color using a new color
object
– Color newColor = new Color(red,green,blue);
– Pixel.setColor(newColor);
Georgia Institute of Technology
Using Classes in Packages
• All classes in the Java language are in a
package
– You can use any class in java.lang
• System, Math, Object
• For classes in other packages you need to
import them
– import java.awt.Color;
– Import java.awt.*; //import all classes in this package
• To use the short name: Color
• Or use the fully qualified name
– packageName.ClassName
Georgia Institute of Technology
Undefined Class Error
• If you forget to import
a class
– Yet, you use the short
name for the class
– It won’t compile
• Undefined class error
• Undefined class
errors mean
– You need to import the
class
– You misspelled the
class
Georgia Institute of Technology
Pixel Exercise
• In DrJava
– Pick a file and create a picture object
– Get the array of pixels from the picture object
– Get the 1st pixel from the array of pixels
– Get the red, green, and blue value for this
pixel
– Get the x and y location of this pixel
– Get the color of this pixel
• Get the red, green, and blue values of the color
Georgia Institute of Technology
Changing Pixel Colors
• There are two ways to change the color of
a pixel in a picture
– pixel.setRed(value), pixel.setGreen(value),
pixel.setBlue(value)
– pixel.setColor(color)
• But, you won’t see any change in the
picture
– Until you ask it to repaint
• picture.repaint();
Georgia Institute of Technology
Changing a Color
• The Color class has methods for making a color object
– Lighter
• color.brighter();
– Darker
• color.darker();
• Example
> Color testColor = new Color(168,131,105);
> System.out.println(testColor);
java.awt.Color[r=168,g=131,b=105]
> testColor = testColor.darker();
> System.out.println(testColor);
java.awt.Color[r=117,g=91,b=73]
> testColor = testColor.brighter();
> System.out.println(testColor);
java.awt.Color[r=167,g=130,b=104]
Georgia Institute of Technology
Rounding Errors
• Notice that when you made the color
darker and then lighter the resulting color
was slightly off of the original
– The change is calculated in floating point
– The result is stored in integer form
– The decimal part is lost
• Rounding errors also occur because of the
limited storage for floating point numbers
– We can’t store all the digits in some numbers
Georgia Institute of Technology
Changing a Picture Exercise
> String fileName = "C:/intro-progjava/mediasources/catapillarClipart.jpg";
> Picture picture = new Picture(fileName);
> picture.show();
> picture.getPixel(10,100).setColor(Color.black);
> picture.getPixel(11,100).setColor(Color.black);
> picture.getPixel(12,100).setColor(Color.black);
> picture.getPixel(13,100).setColor(Color.black);
> picture.getPixel(14,100).setColor(Color.black);
> picture.getPixel(15,100).setColor(Color.black);
> picture.getPixel(16,100).setColor(Color.black);
> picture.getPixel(17,100).setColor(Color.black);
> picture.getPixel(18,100).setColor(Color.black);
> picture.getPixel(19,100).setColor(Color.black);
> picture.repaint();
Georgia Institute of Technology
How do we Know if it Worked?
• A very important part of programming is
testing the result
– Just because code compiles and runs without
error doesn’t mean it is correct
– There could be an error in the logic
– It could fail under certain conditions
– It could even return the correct answer but for
the wrong reason
Georgia Institute of Technology
The Picture Explorer
• Tool that creates a
copy of the current
picture and lets you
explore it
– See the color, x, and y
values at the cursor
• To use the tool on a
picture object
– picture.explore();
• Use it to see if the
colors have changed
Georgia Institute of Technology
Changing the Red in a Picture
• One way to change a picture is to reduce
the amount of red in it
– What if we want to decrease it by half?
• If we have a value of 255 what should the new
value be?
• How do we reduce any value by half?
– What if we want to increase it by 25%?
• If we have a value of 125 what should the new
value be?
• How do we increase any value by 25%?
Georgia Institute of Technology
Changing all the Pixels in a Picture
• There are 360 x 181 = 65,160 pixels in the
caterpillar picture
• Do we really want to write the code to
change each one of these
– Get the current pixel
– Get the red value of the current pixel
– Change the red value of the current pixel to
0.5 the original value
– Put the new red value in the current pixel
Georgia Institute of Technology
We Need a Loop (Iteration)
• A way to execute a series of statements
– With something changing each time the
statements are executed
• Different pixel to change
– And some way to tell when we are done with
the repetition
• Some test to see if the loop should stop
Georgia Institute of Technology
Loop Exercise
• Ask a person to clap 12 times
– How does s/he know when to stop?
– What changes each time s/he claps?
• If you are following a recipe that asks you
to stir the ingredients 50 times how would
you do this?
• What if you were trying to break a sit-up
record
– How would you know if you did break it?
Georgia Institute of Technology
Loops often need Counters
• If you want to do something x times you
often need a counter
– That starts at 0
– And you add 1 to it each time you finish doing
the thing you are repeating
– When the counter reaches the number you
are trying to do you stop the loop
• What is the value of the counter the last time the
statements of the loop are executed?
Georgia Institute of Technology
The While Loop
• In Java one way to repeat a block of statements
while an expression is true is to use a while loop
• Create a counter and set it to the start value
• Check that the counter is less then the stop
value
• If it is less than execute the statements in the
loop
• Add one to the counter and go back to check
that the counter is less than the stop value
Georgia Institute of Technology
Total the Numbers from 1 to 100
• What if you want to add all the numbers
from 1 to 100?
– You will need something to hold the total
• What type should it be?
• What value should it start out with?
– You will need something that counts from 1 to
100
• And add that value to the total
• Stop when you get to 100
• What type should it be? What value should it start
with?
Georgia Institute of Technology
While Loop Syntax
• Adding up the numbers from 1 to 100
int counter = 1;
int total = 0;
while (counter <= 100)
{
total = total + counter;
counter = counter + 1;
}
System.out.println(total);
Georgia Institute of Technology
Decrease Red Algorithm
•
To decrease the red value in a picture by 50%
1. Get the array of pixels from the picture
2. Set up an index to start at 0
3. Check if the index is less than the length of the
array
1. If it is go on to step 4 of the loop
2. If it isn’t jump to the first instruction after the loop
4. Get the pixel at the current index from the array of
pixels
5. Get the red value at the pixel
6. Multiply the red value by 0.5
7. Set the red value at the pixel to the reduced red
value
8. Increment the index and go back to step 3
Georgia Institute of Technology
What is an Algorithm?
• An algorithm is a description of the steps
needed to do a task
– Can be written in English
– A recipe is an algorithm
• A program is an implementation of an
algorithm
– in a particular computer language
Georgia Institute of Technology
From Algorithm to Program (code)
• How do we get the array of pixels from the
current picture object?
– We have used
Pixel[] pixels = picture.getPixels();
– But we want to get the array of pixels from the
current object
Pixel[] pixels = this.getPixels();
– Or we can leave off the this
Pixel[] pixels = getPixels();
Georgia Institute of Technology
Loop Algorithm to Code
• How to write (code) the loop?
– Use a while loop with a counter for the index
starting at 0
int index = 0;
– Loop while the index is less than the length of
the array
while (index < pixels.length)
– Get the current pixel from the array of pixels
for the current index
Pixel pixel = pixels[index];
Georgia Institute of Technology
Loop Algorithm to Code - Continued
– Get the red value at the pixel
int redValue = pixel.getRed();
– Decrease the red value by 0.5
redValue = redValue * 0.5;
– Set the pixel red value
pixel.setRed(redValue);
– Add one to (increment) the index
• index = index + 1;
Georgia Institute of Technology
Decrease Red Method
public void decreaseRed()
{
// get the array of pixels for this picture object
Pixel[] pixels = this.getPixels();
// start the index at 0
int index = 0;
// loop while the index is less than the length of the pixels array
while (index < pixels.length)
{
// get the current pixel at this index
Pixel pixel = pixels[index];
// get the red value at the pixel
int redValue = pixel.getRed();
// set the red value to half what it was
redValue = redValue * 0.5;
// set the red for this pixel to the new value
pixel.setRed(redValue);
// increment the index
index = index + 1;
}
}
Georgia Institute of Technology
Comments
• Comments are explanations of your code
to help people understand your code
– They are ignored by the compiler
• There are several kinds in Java
// a comment that lasts to the end of the line
/* a comment that can take up several lines
until a */
/** a Javadoc comment that is used to create
html documentation of your code */
Georgia Institute of Technology
Loss of Precision
• If you try the code on
the previous slide you
will get a compiler
error
– Possible loss of
precision
• It is complaining
about putting a
double value into a int
variable
– Loss of fractional part
Georgia Institute of Technology
Casting to Solve Loss of Precision Error
• It will compile if we tell the compiler we
know about the possible loss of precision
– And that it is intended
• By using a cast to int
redValue = (int) (redValue * 0.5);
• Notice that we cast the result of the multiplication
back to an integer
• Casting is forcing a value into a type
(type) expression
Georgia Institute of Technology
Move Declarations Outside Loops
• When you need a variable in a loop it is best to
declare it before the loop
– Otherwise you are declaring a new variable each time
through the loop
• Which is slower than just changing the value associated with
the variable
• In some languages you must declare all
variables at the beginning of a method (function)
• In Java you can declare variables anywhere in a
method
– As long as you declare them before you use them
Georgia Institute of Technology
Shortcuts for Common Operations
• In programming you often need to add one
to a value
index = index + 1;
• You may use the shortcut
index++; or ++index;
• If you wanted to subtract 1 instead
index = index – 1;
index--; or -- index;
Georgia Institute of Technology
Decrease Red Method Version 2
public void decreaseRed()
{
Pixel pixel = null; // the current pixel
int redValue;
// the amount of red
// get the array of pixels for this picture object
Pixel[] pixels = this.getPixels();
// start the index at 0
int index = 0;
// loop while the index is less than the length of the pixels array
while (index < pixels.length)
{
// get the current pixel at this index
pixel = pixels[index];
// get the red value at the pixel
redValue = pixel.getRed();
// set the red value to half what it was
redValue = (int) (redValue * 0.5);
// set the red for this pixel to the new value
pixel.setRed(redValue);
// increment the index
index++;
}
}
Georgia Institute of Technology
Decrease Red Exercise
• In DrJava
– Add the method decreaseRed() to Picture.java
– Compile the method
– Test it by doing the following in the interactions pane
> String fileName = "C:/intro-prog-java/mediasources/catapillarClipart.jpg";
> Picture picture = new Picture(fileName);
> picture.show();
> picture.explore();
> picture.decreaseRed();
> picture.repaint();
> picture.explore();
Georgia Institute of Technology
Tracing Code
• An important skill to
develop is the ability
to trace code
– Also called walking
through or stepping
through your code
– Look at each line and
predict what will
happen
– Show the variables
and their values
Georgia Institute of Technology
Step Through decreaseRed()
• A picture object was created from the file
“catapillarClipart.jpg” and then was sent the message
decreaseRed()
• The picture object was implicitly passed to the method
decreaseRed()
• Some variables were declared for later use in the loop
Pixel pixel = null;
int redValue;
• The array of pixel objects was returned from sending
getPixels() to the picture object
Pixel[] pixels = this.getPixels();
Georgia Institute of Technology
Step Through decreaseRed() - cont
• An index variable was declared and set to 0
int index = 0;
• The while loop tests if the index is less than the length of the array
while (index < pixels.length) {
– And if so it executes the statements in the body of the loop {}
• It sets the variable pixel to the pixel at the index in the array of pixels
pixel = pixels[index];
• It gets the red value of that pixel
redValue = pixel.getRed();
• it sets the red value to 0.5 * the original value
redValue = (int) (redValue * 0.5);
• It sets the pixel’s red to the new value
pixel.setRed(redValue);
• It increments the index value
index++;
Georgia Institute of Technology
Memory Map of decreaseRed()
width=360
height=181
• What does memory
this
look like the first time
through the loop?
• How about the 2nd pixels R=255,
G=255,
time through?
B=255,
X=0,
pixel
rd
• How about the 3
Y=0
time through?
• How about the last
redValue = 255
time through?
index = 0
Picture: Class
getPixels()
…
R=255,
R=255,
G=255,
G=255,
B=255,
B=255,
X=1,
X=2,
Y=0
Y=0
Pixel: Class
getRed()
setRed()…
Georgia Institute of Technology
…
Increase Red
• What if you want to increase red by 30%
– How would you do that?
• Multiplying by 0.5 reduces the red by 50%
– Multiplying by 1.0 would keep the same red
value
– Multiplying by 1.3 would increase the red by
30%
– Multiplying by 1.7 would increase the red by
70%
Georgia Institute of Technology
Increase Red Algorithm
• To increase the red value in a picture by 30%
1. Get the array of pixels from the picture
2. Set up an index to start at 0
3. Check if the index is less than the length of the array
1.If it is go on to step 4 of the loop
2.If it isn’t jump to the first instruction after the loop
4. Get the pixel at the current index from the array of
pixels
5. Get the red value at the pixel
6. Multiply the red value by 1.3
7. Set the red value at the pixel to the reduced red value
8. Increment the index and go back to step 3
Georgia Institute of Technology
Increase Red: Algorithm to Code
• The algorithm for this method is very
similar to the algorithm for decrease red
– Start with the code for decreaseRed
– Change the line of code that multiplied the
current red value by 0.5 to 1.3
– Change the name of the method
– Change any comments that need changing
Georgia Institute of Technology
increaseRed Method
public void increaseRed()
{
Pixel pixel = null; // the current pixel
int redValue;
// the amount of red
// get the array of pixels for this picture object
Pixel[] pixels = this.getPixels();
// start the index at 0
int index = 0;
// loop while the index is less than the length of the pixels array
while (index < pixels.length)
{
// get the current pixel at this index
pixel = pixels[index];
// get the red value at the pixel
redValue = pixel.getRed();
// increase the red value to 30% more than the original
redValue = (int) (redValue * 1.3);
// set the red for this pixel to the new value
pixel.setRed(redValue);
// increment the index
index++;
}
}
Georgia Institute of Technology
Clear the Blue Values
• What if you want to clear the blue from a
picture
– Set all the blue values to 0 for all the pixels
• The algorithm is similar to decreaseRed()
and increaseRed() except
– You don’t need to get the value out for blue
and multiply it by some value and then set the
blue value
– Just set the blue value to 0
Georgia Institute of Technology
Clear Blue Exercise
• In Picture.java
• Write the object
method
– public void clearBlue()
• That sets the blue
value to 0 for all
pixels in a picture
Georgia Institute of Technology
Faking a Sunset
• If you want to make an
outdoor scene look like it
happened during sunset
– You might want to increase
the red
• But you can’t increase
past 255
– Another idea is to reduce
the blue and green
• To emphasize the red
• Try to reduce the blue and
green by 30%
Georgia Institute of Technology
Faking a Sunset Algorithm
• Reduce the blue and green by 30%
1. Get the array of pixels from the picture
2. Set up an index to start at 0
3. Check if the index is less than the length of the array
1.If it is go on to step 4 of the loop
2.If it isn’t jump to the first instruction after the loop
4. Get the pixel at the current index from the array of
pixels
5. Set the blue value at the pixel to 0.7 times the original
value
6. Set the green value at the pixel to 0.7 times the
original value
7. Increment the index and go back to step 3
Georgia Institute of Technology
Faking a Sunset Method
/**
* Method to fake a sunset by reducing the blue and green in a picture
* by 30%
*/
public void fakeSunset()
{
Pixel pixel = null; // the current pixel
// get the array of pixels for this picture object
Pixel[] pixels = this.getPixels();
// start the index at 0
int index = 0;
// loop while the index is less than the length of the pixels array
while (index < pixels.length)
{
// get the current pixel at this index
pixel = pixels[index];
// set the blue value to 0.7 times the original blue value
pixel.setBlue((int) 0.7 * pixel.getBlue());
// set the green value to 0.7 times the original green value
pixel.setGreen((int) 0.7 * pixel.getGreen());
// increment the index
index++;
}
}
Georgia Institute of Technology
A For Loop
• Programmers like shortcuts
– Especially those that reduce errors
– And mean less typing
• We have been using a while loop with an index
– We had to declare the index variable and initialize it
before the loop
• If you forget this there will be a compiler error
– We had to increment the index in the loop
• If you forget this it will be an infinite loop
• The shortcut for this is a For Loop
Georgia Institute of Technology
For Loop Syntax
• for (initialization area; continuation test;
change area)
– Initialization area
• Declare variables and initialize them
– Continuation test
• If true do body of loop
• If false jump to next statement after the loop
– Change area
• Change the loop variables
– Increment or decrement them
Georgia Institute of Technology
Comparison of While and For Loops
int index = 0;
while (index < pixels.length)
{
statements
.
.
.
index++;
}
for (int i=0; i < pixels.length; i++)
{
statements
.
.
.
}
Georgia Institute of Technology
Change clearBlue() to use a For Loop
/**
* Method to clear the blue from the picture (set
* the blue to 0 for all pixels)
*/
public void clearBlue()
{
Pixel pixel = null; // current pixel in loop
/**
* Method to clear the blue from the picture (set
* the blue to 0 for all pixels)
*/
public void clearBlue()
{
// get the array of pixels from the current picture
Pixel[] pixels = this.getPixels();
// declare the variable that will refer to the current pixel
Pixel pixel = null;
// get the array of pixels from the current picture
Pixel[] pixels = this.getPixels();
// declare the index and initialize it to 0
int index = 0;
// loop through all the pixels
for (int i = 0; i < pixels.length; i++)
{
// get the current pixel
pixel = pixels[i];
// loop through all the pixels
while (index < pixels.length)
{
// get the current pixel
pixel = pixels[index];
// set the blue on the pixel to 0
pixel.setBlue(0);
// set the blue on the pixel to 0
pixel.setBlue(0);
index++;
}
}
}
}
Georgia Institute of Technology
Using System.out.println() in a Loop
• One way to check what is happening in
your program is to add
– System.out.println(expression);
• You might add this to the loop to check the
value of ‘i’ during it.
– And to verify that the increment happens after
the last statement in the loop
Georgia Institute of Technology
Change to For Loop Exercise
• Edit fakeSunset() and change it from using
a while loop to using a for loop
– Move the declaration of the index to the for
loop initialization area
– Move the index increment to the for loop
change area
– Execute the code to make sure it still works
Georgia Institute of Technology
Negating an Image
• How would you turn a
picture into a
negative?
– White should become
black
• 255,255,255 becomes
0,0,0
– Black should become
white
• 0,0,0 becomes
255,255,255
Georgia Institute of Technology
Negate Algorithm
• Subtract current value from 255 for red, green,
and blue
1. Get the array of pixels from the picture
2. Loop starting an index at 0 and incrementing by 1
3. Check if the index is less than the length of the array
1.If it is go on to step 4 of the loop
2.If it isn’t jump to the first instruction after the loop
4. Get the pixel at the current index from the array of
pixels
5. Set the red value to 255 – current red value
6. Set the blue value to 255 – current blue value
7. Set the green value to 255 – current green value
8. Increment the index and go back to step 3
Georgia Institute of Technology
Negate Method
/**
* Method to negate the picture
*/
public void negate()
{
Pixel pixel = null;
// get the array of pixels
Pixel[] pixels = this.getPixels();
// loop through all the pixels
for (int i = 0; i < pixels.length; i++)
{
// get the current pixel
pixel = pixels[i];
// set the pixel color values to the new values
pixel.setRed(255 - pixel.getRed());
pixel.setGreen(255 - pixel.getGreen());
pixel.setBlue(255 - pixel.getBlue());
}
}
Georgia Institute of Technology
Changing to Grayscale
• Grayscale ranges from black to white
– The red, green, and blue values are the same
• How can we change any color to gray?
– What number can we use for all three values?
• The intensity of the color
– We can average the colors
• (red + green + blue) / 3
– Example
• (15 + 25 + 230) / 3 = 90
Georgia Institute of Technology
Grayscale Algorithm
• Set color values to the average of the original values
1. Get the array of pixels from the picture
2. Loop starting an index at 0
3. Check if the index is less than the length of the array
1.If it is go on to step 4 of the loop
2.If it isn’t jump to the first instruction after the loop
4. Get the pixel at the current index from the array of
pixels
5. Calculate the average of the current values
6. Set the red value to the average
7. Set the blue value to the average
8. Set the green value to the average
9. Increment the index and go to step 3
Georgia Institute of Technology
Grayscale Method
/**
* Method to change the picture to gray scale
*/
public void grayscale()
{
Pixel pixel = null;
int intensity = 0;
// get the array of pixels
Pixel[] pixels = this.getPixels();
// loop through all the pixels
for (int i = 0; i < pixels.length; i++)
{
// get the current pixel
pixel = pixels[i];
// compute the intensity of the pixel (average value)
intensity = (int) ((pixel.getRed() + pixel.getGreen() +
pixel.getBlue()) / 3);
// set the pixel color to the new color
pixel.setColor(new Color(intensity,intensity,intensity));
}
}
Georgia Institute of Technology
Grayscale Result
Georgia Institute of Technology
Luminance
• We perceive blue to be darker than red,
and green
– Even when the same amount of light is
reflected
• A better grayscale model should take this
into account
– Weight green the highest (* 0.587)
– red less (* 0.299) and
– blue the very least (* 0.114)
Georgia Institute of Technology
Grayscale with Luminance Exercise
• Create a new method
grayscaleWithLumina
nce
• Using the new
algorithm for
calculating intensity
Georgia Institute of Technology
Summary
• Pictures have a grid of pixels
– You can change the picture by changing the
color of the pixel
– You will need to repaint the picture
• Arrays let you store and retrieve values of
the same type using an index
• You will need to import classes that you
wish to use that aren’t in java.lang
• Loops allow you to execute a block of
statements zero to many times
Georgia Institute of Technology