Filter an image (eg Picoli)

[MiniMacLean]

I was wondering.. how would you put a filter of some kind on an image like the app Picoli (goes to iTunes) does so that i could make a picture Black and White or Negative

I dont have a clue, i have searched in the documentation but cant find anything, is it something more complicated than i think like CoreGraphics or something?

[MiniMacLean]

does anyone know how to do this?

[scottiphone]

It's all done from scratch. You'll have to write your own image processing functions.
Squiggles does many of these same things.

[PhoneyDeveloper]

I don't think there are any built-in filters or a way to apply a filter directly to a UIImage. You need to use coregraphics. You build a cgbitmapcontext, draw your image into it, apply whatever filter you want to the bitmap data, and get an image from the bitmapcontext.

You'll need to come up with whatever logic you need to filter the pixels. One way to make an RGB image bw just average the three channels and write the average back to all three channels.

[MiniMacLean]

aha thanks, so basically its not that simple and its not worth making a free app that does this?

[PhoneyDeveloper]

I don't think this is complicated at all. We won't be seeing Photoshop on the phone anytime soon so there may not be any competition. Having a few filters to adjust contrast, brightness, maybe allow writing text onto the image might be nice.

Might make a nice 0.99 cents app.

[MiniMacLean]

yeah.. its not a good thing for a first app though.. i need to learn basics of obj-c and i havent really tried much but i dont have much time but i really want to make something... i just gotta be patient and learn it i suppose