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Introduction to Computer Science – Chapter 10. CSc 2010 Spring 2011 Marco Valero. Overview. Review image basics Making pictures Image processing Shrinking and enlarging Blurring and sharpening Negative and embossing Robot vision. Image basics.

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Review image basics

Making pictures

Image processing

Shrinking and enlarging

Blurring and sharpening

Negative and embossing

Robot vision


Image basics

We used takePicture and show to respectively take and show pictures already

We’ve also seen savePicture as a means to save a snapshot to disk

makePicture(<filename>) will load a picture from disk and return a picture object

myPic = makePicture(pickAFile())


Image basics

Height and width can be retrieved from a picture

getHeight(<pic>) and getWidth(<pic>)


We can call show(myPic, ‘my title’) to create a window with a title


Making pictures

Rather than taking pictures, we can create our own

width = height = 100

newPic = makePicture(width, height, black)


Each is a byte, 0-255

We can loop through each pixel just like a matrix and change the value


Image processing

We can think of the bitmap as a matrix then any transformation from one picture to another is a matrix transformation

500x500 pixel bitmap

250k pixels

If 10 operations per transformation that’s 2.5 mil ops!

Image processing is is intensive


Shrinking & enlarging

If we wanted to shrink a given n x n image by a factor of f

Result size is n/f x n/f

Bitmap[x*f, y*f] -> NewBitmap[x, y]

Enlarging is the inverse

Result size is n*f x n*f

Bitmap[x/f, y/f] -> NewBitmap[x, y]


Blurring & sharpening

Pixel transformation as a result of its local neighbors’ values

Blurring is done by setting a pixels value to the averages of its neighbors

V = sum([getRed(up),getRed(left),…]) / 5

Sharpening is done by subtracting the sum of its neighbors

V = 5*getRed(self) – sum([neighborvalues])


Negative & embossing

To create a negative of an image we simply subtract 255 from the current value

V = 255 – getRed(pixel)

Creating an embossed effect is done by subtracting a neighbors value from a pixel

V = getRed(pixel) – getRed(neighbor)


Robot vision

Are computers good at recognizing objects?

Are _we_ good at recognizing objects?

What would a simple tracking code look like?


Robot vision

What if we only focused on the object?

We can use high contrast filter

What are the issues with this?

Blob filtering


Compare to older program