Need help cutting out images

Question

Hey
I realize what Im asking for might be complicated. But any
help or direction I can get will be appreciated.
I want to right something that will take a photo realistic
image, say maybe a 400x300 photo of anything really, and cut out
peices of the photo, so that I can manipulate these peices after.
For example...if its a photo of a guy riding a bike and hes wearing
a blue shirt....I want to cut out the blue shirt part and change
its color on the fly, just by clicking on the blue shirt.
Any ideas??
Oh and does this process have a name?

Answer 1

Yes, you're right - it is complicated!
The reason is that with a photo of a guy wearing a blue
shirt, that blue shirt is actually made up of hundreds of different
subtle shades of blue.
So to implement this, you'd need to perform a number steps,
some of which are fairly complex:
1) allow the user to select a point in the image
2) read the colour at that point. You might find you need to
take an average of a small area around that point to get a better
approximation of the percieved colour at that point because the
colour of pixels within a seemingly 'flat' area of colour can
actually vary significantly. (this is why the photoshop inkdropper
tool offers 3x3 and 5x5 average options).
3) gradually 'scan' outwards from the pixel coordinate
clicked on, checking each adjacent pixel in the image and comparing
the difference in colour value against the initial colour selected
(using getPixel). If it is within a certain tolerance, you can
include it in the selection. You'll need to create an array or
another image object to store the results in. Repeat this process
until there are no more adjacent pixels that fall within the colour
tolerance range.
4) Use an RGB->HSB routine to convert the colour values to
HSB, so that you can then adjust the 'Hue' value, and finally
convert back to RGB. I have one here:
http://robotduck.com/content/articles/director/imageManipulation/shiftHue.txt
And whether it has a name?..
well, the tool which selects an area within a certain colour
range in photoshop is called the 'magic wand', so I guess that's a
good way to refer to it - a magic wand function. And to change the
colour by 'rotating' the colour values through the colour spectrum
(which is what my example code does) is called 'shifting the hue'
of the colours.
hope this helps!
- Ben