PaintBucket Algorithm

Paint Bucket is a common tool for image editing applications (Photoshop, Paintshop Pro etc..). Main purpose of this tool is find and paint an area that has similar colored pixels. So it's algorithm much more harder to code and compute than a normal paint brush or pencil brush. Because paint bucket algorithm has, a search and determine an area with similar color, different with other tools.

And on the other hand, Paint Bucket algoritm has very similar with path finder algorithm, they both have a search algorithm. Path finder algorithm search and select the best way, this algorithm search and fill all the ways with selected color.

Main route of algorithm

Here it is a sample 19x19 pixel work area that seperated with black lines. Bright red means that the work area. X axis is written in red, Y Axis is written in orange.

First user select a start point (marked as red in figure - 11,11). Algorithm marked the startpoint as a allowed point and add it to array. Then determine the north, east, west and south neighbour of it (marked as yellow in figure). Check each point, if it similar with startpoint, adds it to the postponed points array for future process. After that progress, code will have a 4 postponed point for future check. And starts the checking of them point by point. And if the checked point is similar than it adds that point to the postponeds array and also allowed points array. If not, it does nothing and check if any postponed point available.

This progress is continues up to postoned array is reach zero lenght and all waiting check operations has finished.

Very common question at this time that "Why we are using a postponeds array, Why we aren't using a recursive routine",
Answer: if we don't use a array, all waiting operations stored at stack of executable. In the future of progress we will have lots of point to be waiting for check. And because of that, stack will probably overflow acording to dimensions of image. In tests i get "out of stack" error with images bigger than 200x200 pixel.

After the operation image become like that

There is only an area (on the bottom corner-right) where was not filled, because it has no gate that brush can come in.

Finally, all this algorithm written in vb.net is included with project. Please check the codes and try to understand if i am not clear.

And Test Application is very functional and reusable with all this and other MDI based applications. You can freely use and distrubute it in personal and opensourced projects (please not in commercial projects).

Test Application has Undo and Redo function (with 5 history limitation), "open", "save", "save as" and "close" functions with four common image format.

At the end, a last question: "Why we aren't use a multitheread routine for speeding up the progress"
Answer: I think of it and try as well but nothings changed, because of GDI+. GDI+ in .net is very new and unstable. It occurs lots of unrecognized and silly errors. For example in Undo Function, when you get a clone of image to the memory. It gives an silly error like "Undetermined Error". I have to do with "memory stream" after trying 3 other routine (all of them occurs very unlikely error). I hope that all that GDI+ problems solved on VS2005.

Have a nice coding
Sukru Alatas
ferrodoxin@hotmail.com

27th Aug 05