For the activities on this page, I have used the sample picture flowers.jpg   You can use an image of your own, or you can download the flowers image and use it.  If you use an image of your own, make sure it is not too large.  Less than 400x400 pixels would be best.

Exploring Pictures

JES has an inbuilt tool for exploring pictures.

In the command window, load a picture of your choice by typing pict=makePicture(pickAFile())

Now from the menus at the top, choose Media Tools >Picture Tool.  Select pict (the location of your image).  Now you can get information about your image and the colours at various locations.

Loading an Image and a Pixel

From previously, you need the following commands to get at your pixels:

Load a picture of your choice into a storage location named pict by typing the following in the command window:

pict=makePicture(pickAFile())

To load the pixel at coordinates (1,1) into a location named pixel, type the following

pixel=getPixel(pict, 1,1)

 

X and Y Coordinates of a Pixel

Pixels know where they came from. You can ask them their x and y coordinates with getX and getY.

 

 >>> print getX(pixel)
1
>>> print getY(pixel)
1

Getting and Setting Colours for Pixels

You can ask a pixel for its colour with getColor >>> print getColor(pixel)
color r=64 g=65 b=69
Each pixel knows how to getRed and setRed (Green and blue work similarly.) >>> print getRed(pixel)
64
>>> setRed(pixel,255)
>>> print getRed(pixel)
255
You can set the colour with setColor. Colour objects know their red, green, and blue components. >>> setColor(pixel,color)
You can make new colours with makeColor. >>> newColor=makeColor(0,100,0)
>>> print newColor
color r=0 g=100 b=0
repaint

Picture displays don't automatically get updated.  If you show your picture and then change the pixels, you will need to use repaint to update it

 >>>repaint(pict)

 

Modifying Some Pixels

The following example program will modify 4 pixels of the image and change them to green.

They are the pixels at coordinates (50,100) (51,100) (52, 100) (53, 100)

You can see the effect on the adjacent image.

So do we need to change every pixel individually?  The answer is yes, but the good news is that we can write programs to make it quick and efficient.
You won't always see changes you make in your picture straight away because the picture you see on the screen does not automatically get updated.  You need to use the repaint command to update it.

repaint(pict)

Saving Your Finished Picture

When you have finished manipulating a picture, you can write it to a new file by using writePictureTo then giving a path and filename to save it to.  Make sure you put .jpg on the end of the filename. 

Note: On Windows machines, you need to put an r in front of the filepath.  That's so that Python correctly interprets it as a path.

>>> writePictureTo(picture,r"c:\docs\newpicture.jpg")

 

Other Picture Functions

JES has many other picture functions that you can use, such as addLine, addOval, addRect, addText, and more.  Look in the JES help for information on how to use them.

Colour Distance

You can compare two colours by subtracting one from the other.  If we do that we get a new colour whose red, green and blue components are the differences of each.

Colour distance lets you see how close two shades of a colour are.  If you have two colours (red1, green1, blue1) and (red2, green2, blue2), then the colour distance can be calculated using the following formula:

Help

Use the help menu in JES to find out about some more picture functions.