As promised, here is the FAST (Features from Accelerated Segment Test) implementation in RealBasic! And as you’ll notice, this is extremely fast!
Wiki:
AST is an acronym standing for Accelerated Segment Test. This test is a relaxed version of the SUSAN corner criterion. Instead of evaluating the circular disc only the pixels in a Bresenham circle of radius r around the candidate point are considered. If n contiguous pixels are all brighter than the nucleus by at least t or all darker than the nucleus by t, then the pixel under the nucleus is considered to be a feature. This test is reported to produce very stable features.[17] The choice of the order in which the pixels are tested is a so called Twenty Questions problem. Building short decision trees for this problem results in the most computationally efficient feature detectors available.
The first corner detection algorithm based on the AST is FAST (Features from Accelerated Segment Test). Although r can in principle take any value, FAST uses only a value of 3 (corresponding to a circle of 16 pixels circumference), and tests show that the best results are achieved with n being 9. This value of n is the lowest one at which edges are not detected. The order in which pixels are tested is determined by the ID3 algorithm from a training set of images. Confusingly, the name of the detector is somewhat similar to the name of the paper describing Trajkovic and Hedley’s detector.
It is the RealBasic translation of the nonmaximal FAST-9 written by Edward Rosten
http://www.edwardrosten.com/work/fast.html
With this library you can find Corners very fast within a picture.
and it can do this under e.g. different light intensities:
Again, the RealBasic engine has a simple interface so you can focus on the fun stuff!
dim FCD as new ABFastCornerDetector
dim tmpXYTraining(-1) as ABXY
dim i as integer
dim j as integer
dim pic as Picture
dim tmpPic as Picture
dim DownSample as integer
dim build2Dim as Boolean = true
Dim f as FolderItem
dim ft1 as new filetype
ft1.name = "picture"
ft1.Extensions = ".png;.bmp;.jpg;.jpeg"
dim dlg as OpenDialog
dlg = new OpenDialog
dlg.Title = "Pick picture"
dlg.PromptText = "Pick a picture to compare"
dlg.Filter=ft1
if dlg.InitialDirectory = nil then
dlg.InitialDirectory = GetFolderItem("")
end if
f = dlg.ShowModal
if f <> nil then
if f.Exists then
pic = f.OpenAsPicture
else
Return
end if
else
Return
end if
' these are then numbers you can play with
FCD.threshold_detection = 20
FCD.threshold_scoring = 0
DownSample = 2
' do the FAST detection
tmpXYTraining = FCD.detectFASTCornerFeatures(pic,DownSample, build2Dim)
tmpPic = NewPicture(pic.Width, pic.Height, 32)
tmpPic.Graphics.DrawPicture pic,0,0
tmpPic.Graphics.ForeColor = &cFF0000
' and draw them
for i = 0 to UBound(tmpXYTraining)
tmpPic.Graphics.DrawLine tmpXYTraining(i).x*DownSample - 3, tmpXYTraining(i).y*DownSample, tmpXYTraining(i).x*DownSample + 3, tmpXYTraining(i).y*DownSample
tmpPic.Graphics.DrawLine tmpXYTraining(i).x*DownSample, tmpXYTraining(i).y*DownSample-3, tmpXYTraining(i).x*DownSample, tmpXYTraining(i).y*DownSample+3
next
Canvas1.Graphics.FillRect 0,0, 640,480
Canvas1.Graphics.DrawPicture tmpPic,0,0
You can download the FAST engine from: http://www.gorgeousapps.com/ABFAST.zip
Until the next post!
if you like my work
