18.1. Using Repetition with Images¶
forloops and nested
forloops to repeat actions on pixels in an image.
Understand the pattern (the steps) used in modifying all the pixels in an image.
Describe how multiple classes (Image and Pixel) interact.
Images (pictures) on a computer are broken up into little bits called pixels, for picture (pix) elements (els). These are laid out on a grid, from left to right (horizontal or x dimension) and top to bottom (vertical or y dimension).
Pixels are quite small. Even the small image below has 180 columns and 240 rows of pixels. Each pixel has a color associated with it: an amount of redness, an amount of greenness, and an amount of blueness. Let’s remove the red from this picture. Now, there are lot of lines in the program below, but fortunately, you can ignore most of them. The Audio Tour explains the important lines. Press to hear the audio tour explanation. When you run this program it may take several minutes to show the changed image.
The program above can take several minutes to execute on the
arch.jpg picture. But we’re not stuck using just the arch image. You can
change the file name in the program above to the URL for any small photo that is on the internet.