The Sobel Function

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Scherererer	Created : 19 July 2009 Language : Blitz The Sobel Function A method used in image processing & edge finding
So, I was a bit disappointed that so many people here thought that math wasn't useful, especially among a coding community such that we're in. In an effort to get you all more interested into math, here is a quickie demo of the Sobel method, which uses directional derivatives (Calculus) to find the edges of things in a picture. There are many applications for this, especially in the area of Computer Vision, some of which I do for building autonomous robots. I plan on eventually turning this into an article, and hopefully making more articles with information on how math can be directly applied to coding, and how you can use some of these things to do some really cool stuff. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Sobel Example ;; ;; Demonstrates the Sobel Function, a method ;; ;; used in computer vision processing/edge ;; ;; finding. ;; ;; ;; ;; Written By Michael Scherer (Schererer) ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Graphics 640, 480, 0, 2 f$ = Input$("Type the file name of the image you want processed: ") image = LoadImage(f$) width = ImageWidth(image) height = ImageHeight(image) ;FreeImage(image) EndGraphics Graphics width, height, 0, 2 image = LoadImage(f$) SetBuffer(BackBuffer()) Sobel(image) DebugLog "Processing Completed" WaitKey() EndGraphics End Function Sobel(image) SetBuffer(ImageBuffer(image)) For r=0 To (ImageHeight(image)-2) For c=0 To (ImageWidth(image)-2) pix = ReadPixel(c, r, ImageBuffer(image)) ; Get the color of the current pixel pixRed = pix Shr 16 And 255 Shl 0 pixGreen = pix Shr 8 And 255 Shl 0 pixBlue = pix Shr 0 And 255 Shl 0 pixRight = ReadPixel(c+1, r, ImageBuffer(image)) ; Get the color of the next pixel over pixRightRed = pixRight Shr 16 And 255 Shl 0 pixRightGreen = pixRight Shr 8 And 255 Shl 0 pixRightBlue = pixRight Shr 0 And 255 Shl 0 ; Take the partial derivative in the x direction xDerivRed# = Float#(pixRightRed - pixRed)/2.0 xDerivGreen# = Float#(pixRightGreen - pixGreen)/2.0 xDerivBlue# = Float#(pixRightBlue - pixBlue)/2.0 ; Get the magnitude of the partial wrt x ; Just the distance formula, squareroot(x^2 + y^2 + z^2) DxMag# = Sqr(xDerivRed#xDerivRed# + xDerivGreen#xDerivGreen# + xDerivBlue#xDerivBlue#) pixDown = ReadPixel(c, r+1, ImageBuffer(image)) ; Get the color of the next pixel down pixRightRed = pixDown Shr 16 And 255 Shl 0 pixRightGreen = pixDown Shr 8 And 255 Shl 0 pixRightBlue = pixDown Shr 0 And 255 Shl 0 ; Take the partial derivative in the y direction yDerivRed# = Float#(pixRightRed - pixRed)/2.0 yDerivGreen# = Float#(pixRightGreen - pixGreen)/2.0 yDerivBlue# = Float#(pixRightBlue - pixBlue)/2.0 ; Get the magnitude of the partial wrt y ; Just the distance formula, squareroot(x^2 + y^2 + z^2) DyMag# = Sqr(yDerivRed#yDerivRed# + yDerivGreen#yDerivGreen# + yDerivBlue#yDerivBlue#) ; Magnitude of Del(F) DelFMag# = Sqr(DxMag#DxMag# + DyMag#DyMag#) outPix = (255 Shl 24) Or (Int(DelFMag#) Shl 16) Or (Int(DelFMag#) Shl 8) Or Int(DelFMag#) ;DebugLog c + " " + r + " " + Hex(outPix) WritePixel c, r, outPix, FrontBuffer();ImageBuffer(sobelOut) Next Next End Function --v

Comments
Wednesday, 12 May 2010, 12:33
Longarm	Awesome effect! (could it be sped up for a realtime useage, maybe with lock/unlock buffer?)
Wednesday, 12 May 2010, 12:47
JL235	Yes, it appeares instantly for me. I'd imagine there might also be some clever algorithm changes you can make to avoid reading a pixel 3 times; to get that down to a single read per pixel. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Sobel Example ;; ;; Demonstrates the Sobel Function, a method ;; ;; used in computer vision processing/edge ;; ;; finding. ;; ;; ;; ;; Written By Michael Scherer (Schererer) ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Graphics 640, 480, 0, 2 f$ = Input$("Type the file name of the image you want processed: ") image = LoadImage(f$) width = ImageWidth(image) height = ImageHeight(image) ;FreeImage(image) EndGraphics Graphics width, height, 0, 2 image = LoadImage(f$) SetBuffer(BackBuffer()) Sobel(image) DebugLog "Processing Completed" WaitKey() EndGraphics End Function Sobel(image) SetBuffer(ImageBuffer(image)) LockBuffer ImageBuffer(image) LockBuffer FrontBuffer() For r=0 To (ImageHeight(image)-2) For c=0 To (ImageWidth(image)-2) pix = ReadPixelFast(c, r, ImageBuffer(image)) ; Get the color of the current pixel pixRed = pix Shr 16 And 255 Shl 0 pixGreen = pix Shr 8 And 255 Shl 0 pixBlue = pix Shr 0 And 255 Shl 0 pixRight = ReadPixelFast(c+1, r, ImageBuffer(image)) ; Get the color of the next pixel over pixRightRed = pixRight Shr 16 And 255 Shl 0 pixRightGreen = pixRight Shr 8 And 255 Shl 0 pixRightBlue = pixRight Shr 0 And 255 Shl 0 ; Take the partial derivative in the x direction xDerivRed# = Float#(pixRightRed - pixRed)/2.0 xDerivGreen# = Float#(pixRightGreen - pixGreen)/2.0 xDerivBlue# = Float#(pixRightBlue - pixBlue)/2.0 ; Get the magnitude of the partial wrt x ; Just the distance formula, squareroot(x^2 + y^2 + z^2) DxMag# = Sqr(xDerivRed#xDerivRed# + xDerivGreen#xDerivGreen# + xDerivBlue#xDerivBlue#) pixDown = ReadPixelFast(c, r+1, ImageBuffer(image)) ; Get the color of the next pixel down pixRightRed = pixDown Shr 16 And 255 Shl 0 pixRightGreen = pixDown Shr 8 And 255 Shl 0 pixRightBlue = pixDown Shr 0 And 255 Shl 0 ; Take the partial derivative in the y direction yDerivRed# = Float#(pixRightRed - pixRed)/2.0 yDerivGreen# = Float#(pixRightGreen - pixGreen)/2.0 yDerivBlue# = Float#(pixRightBlue - pixBlue)/2.0 ; Get the magnitude of the partial wrt y ; Just the distance formula, squareroot(x^2 + y^2 + z^2) DyMag# = Sqr(yDerivRed#yDerivRed# + yDerivGreen#yDerivGreen# + yDerivBlue#yDerivBlue#) ; Magnitude of Del(F) DelFMag# = Sqr(DxMag#DxMag# + DyMag#DyMag#) outPix = (255 Shl 24) Or (Int(DelFMag#) Shl 16) Or (Int(DelFMag#) Shl 8) Or Int(DelFMag#) ;DebugLog c + " " + r + " " + Hex(outPix) WritePixelFast c, r, outPix, FrontBuffer();ImageBuffer(sobelOut) Next Next UnlockBuffer ImageBuffer(image) UnlockBuffer FrontBuffer() End Function --v Awesome effect btw, I really like it.
Friday, 23 July 2010, 15:10
Andy_A	Sorry it took so long to comment on this, but it's great! It worked on every type of picture (even pictures of text). Nice one!

The Sobel Function

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