Python: Modifying Pictures Using Loops

Review JES command area – program area Defining/using functions specifying a sequence of steps for what the function should do. JES Functions for file manipulation JES->Files JES Functions for interacting with user JES-->Input/Output JES Functions for picture manipulation JES-->Pictures

Reminder: Manipulating Pictures >>> pic1 = makeEmptyPicture(200,100) >>> show(pic1) >>> setAllPixelsToAColor(pic1, red) >>> show(pic1) >>> addText(pic1,30,50,“hello") similarly can add rectangles, lines, etc.

Reminder: Common errors >>> file = pickAFile() >>> pic = makePicture(file) >>> show(file) The error was:sample Name not found globally. A local or global name could not be found. You need to define the function or variable before you try to use it in any way. >>> show(pic) >>> print pic Picture, filename C:\Documents and Settings\mpapalas\Desktop\sample.jpg height 1200 width 1600 Oops!

Making new Colors Some names for common colors are predefined – try using the names: yellow, black, white, etc. makeColor() takes red, green, and blue values (in that order) between 0 and 255, and returns a Color object pickAColor() lets you use a color chooser and returns the chosen color

Color:(108,86,142) Position: (12,9) x = 12 y = 9 red=108green=86blue=142

Encoding RGB Colors go from (0,0,0) to (255,255,255) >>> pic2 = makeEmptyPicture(200,100) >>> show(pic2) >>> seafoam = makeColor(153, 255, 204) >>> setAllPixelsToAColor(pic2, seafoam ) >>> show(pic2)

Manipulating pixels getPixel(picture,x,y) gets a single pixel. getPixels(picture) gets all of them in an array

Color:(108,86,142) Position: (12,9) x = 12 y = 9 red=108green=86blue=142 >>> pixel=getPixel(picture,12,9) >>> print pixel Pixel, red=108 green=86 blue=142 >>> allThePixels=getPixels(picture) >>> print allThePixels[0] Pixel red=191 green=149 blue=120

What can we do with a pixel? getRed(), getGreen(), and getBlue() are functions that take a pixel as input and return a value between 0 and 255 setRed(), setGreen(), and setBlue() are functions that take a pixel as input and a value between 0 and 255

We can also get, set, and modify Colors getColor() takes a pixel as input and returns a Color object with the color at that pixel setColor() takes a pixel as input and a Color, then sets the pixel to that color We also have functions that can makeLighter() and makeDarker() an input color Last time we saw that we can also create colors: –makeColor() takes red, green, and blue values (in that order) between 0 and 255, and returns a Color object –pickAColor() lets you use a color chooser and returns the chosen color

Demonstrating: Manipulating Colors >>> print getRed(pixel) 168 >>> setRed(pixel,255) >>> print getRed(pixel) 255 >>> color=getColor(pixel) >>> print color color r=255 g=131 b=105 >>> setColor(pixel,color) >>> newColor=makeColor(0,100,0) >>> print newColor color r=0 g=100 b=0 >>> setColor(pixel,newColor) >>> print getColor(pixel) color r=0 g=100 b=0 >>> print color color r=81 g=63 b=51 >>> print newcolor color r=255 g=51 b=51 >>> print color color r=168 g=131 b=105 >>> print makeDarker(color) color r=117 g=91 b=73 >>> print color color r=117 g=91 b=73 >>> newcolor=pickAColor() >>> print newcolor color r=255 g=51 b=51

We can change pixels directly… >>> file= pickAFile() >>> pict=makePicture(file) >>> show(pict) >>> setColor(getPixel(pict,10,100),yellow) >>> setColor(getPixel(pict,11,100),yellow) >>> setColor(getPixel(pict,12,100),yellow) >>> setColor(getPixel(pict,13,100),yellow) >>> repaint(pict)

Media Tools JES Picture function OR Media Tools menu How do you find out what RGB values you have? And where?

Repeating an action for all the pixels in a picture Example: for p in getPixels(picture): value = getRed(p) setRed(p, value*0.5)

Repeating an action for all the pixels in a picture decreaseRed() Example: def decreaseRed(picture): for p in getPixels(picture): value = getRed(p) setRed(p, value*0.5)

More examples: decreaseGreen() decreaseBlue() clearBlue() lighten() darken() negative() grayScale()

Saving to a file setMediaPath(): Prompts the user to pick a folder on the computer. JES then will look for files in that directory unless given a full path, i.e. one that starts with "c:\" writePictureTo(picture, path): picture: the picture you want to be written out to a file path: the path to the file you want the picture written to Takes a picture and a file name (string) as input, then writes the picture to the file as a JPEG. Example: writePictureTo(pic, “mypic.jpg”)

Assignment Create picture manipulation functions that do the following: 1.Decrease red by 10% 2.Decrease green by 10% 3.Decrease blue by 10% 4.Make the picture darker by decreasing red, green, and blue by 10% 5.Make a grayscale version of the image and then negate it (B/W negative)

Next time: Repetition Conditionals Lists Menu-driven program

Repetition for number in range(0,N): pic =.... filename = “pic” + str(number) writePictureTo(pic, filename)

Conditionals if age < 18: showInformation(“Sorry, not allowed to vote yet.”) else: showInformation(“Please select candidate.”)

Lists [“hi”, “hello”, “howdy”, “hiya”, “yo”] [10, 23, 15] [] range(0,6) range(1,4) range(3,8)

Preview of next assignment Create a menu-driven picture manipulation program that allows the user to make various changes to images. Here is the algorithm: welcome the user to your program get the user to select a picture to work on show(picture) ask the user to select an option from a list of numbers: –reduce red –reduce green –reduce blue –posterize –grayscale – repaint(picture) ask user whether to save the picture work, and if the response is “yes”, save it show goodbye/thank you message