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CIELAB system DeltaE values?

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T O P I C R E V I E W
AndyColmes	Posted - Jan 25 2013 : 14:00:26 I've been asked to get DeltaE values of color differences in the CIELAB color system. I have no resource on this and I was wondering if ImageEn can help in any way regarding this. Currently, I use ImageEn to get the RGB values of a pixel area, but how do I get the DeltaE values? Any help in this is very much appreciated. Thanks.
7 L A T E S T R E P L I E S (Newest First)
fab	Posted - Feb 09 2013 : 05:34:33 I try...please re-check this code. Also I cannot guarantee that it works correctly or at all and I cannot support it! All value types are double or extended, except for color1 and color2 that are TIECIELab. color1 := ImageEnView1.IEBitmap.Pixels_ieCIELab[col, row]; color2 := ImageEnView2.IEBitmap.Pixels_ieCIELab[col, row]; // l and c from CMC(l:c), for example CMD(1:1) l = 1 and c = 1. Read the link for more info. l := …. c := …. a1 := color1.a; b1 := color1.b; L1 := color1.L; a2 := color2.a; b2 := color2.b; L2 := color2.L; C1 := sqrt( sqr(a1) + sqr(b1) ); C2 := sqrt( sqr(a2) + sqr(b2) ); DeltaC := C1 - C2; DeltaL := L1 - L2; DeltaA := a1 - a2; DeltaB := b1 - b2; DeltaH := sqrt( sqr(DeltaA) + sqr(DeltaB) - sqr(DeltaC) ); if (a1 = 0) and (b1 > 0) then H1 := Pi / 2 else if (a1 = 0) and (b1 < 0) then H1 := -Pi / 2 else H1 := ArcTan2(b1, a1); H1 := RadToDeg(H1); if H1 < 0 then H1 := H1 + 360 else if H1 >= 360 then H1 := H1 - 360; if (H1 <= 345) and (H1 >= 164) then T := 0.56 + abs(0.2 * cos(DegToRad(H1 + 168))) else T := 0.36 + abs(0.4 * cos(DegToRad(H1 + 35))); F := sqrt( Power(C1, 4) / (Power(C1, 4) + 1900) ); if L1 < 16 then SL := 0.511 else SL := (0.040975 * L1) / (1 + 0.01765 * L1); SC := (0.0638 * C1) / (1 + 0.0131 * C1) + 0.638; SH := SC * (F * T + 1 - F); DeltaE := sqrt( sqr(DeltaL / l * SL) + sqr(DeltaC / c * SC) + sqr(DeltaH / SH));
AndyColmes	Posted - Feb 09 2013 : 03:04:38 Thank you Fabrizio. I will try that. Can you help with the formula for Delta E (CMC)? I think this is the formula that is needed for my application. Thanks in advance.
fab	Posted - Feb 09 2013 : 02:33:06 I think you have enough info: just loop among the squares, getting pixels with Pixels_ieCIELab[] and calculate the avarege for each square.
AndyColmes	Posted - Feb 04 2013 : 02:10:23 I would like to get a 3x3 or 5x5 pixel square and find the average DeltaEs. What would be the good way to do that? Thanks again, Fabrizio.
fab	Posted - Feb 01 2013 : 09:25:23 For the simplest Delta-E (CIE 1976) it is just: deltaE := sqrt(sqr(L1-L2) + sqr(a1-a2) + sqr(b1-b2)) This calculates deltaE of a single pixel, at "col" and "row": var c1, c2: TCIELab; var deltaE: double; c1 := ImageEnView1.IEBitmap.Pixels_ieCIELab[col, row]; c2 := ImageEnView2.IEBitmap.Pixels_ieCIELab[col, row]; deltaE := sqrt(sqr(c1.l-c2.l) + sqr(c1.a-c2.a) + sqr(c1.b-c2.b)); Do you need a single deltaE for the overall image, or a matrix (an image) of DeltaEs?
AndyColmes	Posted - Jan 28 2013 : 17:40:31 Wow, thanks very much Fabrizio. ImageEn never ceases to amaze me. I would appreciate it if you could help in getting any resource on how to apply the formulas in Delphi. Is there a Math component out there that can facilitate this? Thanks again.
fab	Posted - Jan 28 2013 : 07:50:11 If you have a (for example) a TIFF with CIELab image, you can load it using: ImageEnView.LegacyBitmap := false; ImageEnView.IO.NativePixelFormat := true; ImageEnView.IO.LoadFromFile('cielabimage.tiff'); Otherwise, you can load an RGB image and convert it to CIELab: ImageEnView.LegacyBitmap := false; ImageEnView.IO.LoadFromFile('rgbimage.jpg'); ImageEnView.IEBitmap.PixelFormat := ieCIELab; Now you have a matrix of CIELab values, accessible with: cielab := ImageEnView.IEBitmap.Pixels_ieCIELab[col, row]; Where cielab is a TCIELab variable (defined in hyieutils unit). Of course you have to do it also for the other image to compare. Having CIELab values, you can get the Delta E value applying one of the well known formulas, depends by the Delta E you want. Here is some useful links: Delta E (CIE 1976): http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE76.html Delta E (CIE 1994): http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE94.html Delta E (CIE 2000): http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE2000.html Delta E (CMC): http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CMC.html Hope this helps.