Hi guys, i need help understanding how to build a formula for mean and standard deviations for Lab colorspace
I´m trying to build a color transfer algorithm, but i didn´t understood the formulas neither how o create them.
The document i´m reading to build the formula is this (http://www.4shared.com/rar/sVGa3s3X/p66-huang.html)
i have downloaded the PDF - let me see if i can understand it - lol
Tks dedndave
For the regular mean and standard deviations, i succeed to make. The problem is with this weight variable, covariance and Q attributes. I´m not being able to understand how to code them, because i don´t know how to analyse those mathematical formulas
For getting the regular standard deviation, i succedded making this:
[CieLabVariance:
CieLabVariance.Light: R$ 0
CieLabVariance.aFactor: R$ 0
CieLabVariance.bFactor: R$ 0
CieLabVariance.KFactor: R$ 0]
[CieLabMean:
CieLabMean.Light: R$ 0
CieLabMean.aFactor: R$ 0
CieLabMean.bFactor: R$ 0
CieLabMean.KFactor: R$ 0]
[CieLabStdDev:
CieLabStdDev.Light: R$ 0
CieLabStdDev.aFactor: R$ 0
CieLabStdDev.bFactor: R$ 0
CieLabStdDev.KFactor: R$ 0]
Proc GetCieLabStandardDeviation:
Arguments @pColorData, @ImgWidth, @ImgHeight
call CieLabGetMean D@pColorData, D@ImgWidth, D@ImgHeight, CieLabMean
call CieLabGetVariance D@pColorData, CieLabMean, D@ImgWidth, D@ImgHeight
finit
fld R$CieLabVariance.Light | fsqrt | fstp R$CieLabStdDev.Light
fld R$CieLabVariance.aFactor | fsqrt | fstp R$CieLabStdDev.aFactor
fld R$CieLabVariance.bFactor | fsqrt | fstp R$CieLabStdDev.bFactor
;fld R$CieLabVariance.KFactor | fsqrt | fstp R$StdDev.KFactor <------ weight ??????
EndP
Proc CieLabGetMean:
Arguments @pColorData, @ImgWidth, @ImgHeight, @pCieLabMeanStr
Local @iCounter, @Red, @Green, @Blue, @Y, @MaxCount, @MyPixelSrc, @MaxCount2
Structure @TempStorage 44, @HueDis 0, @SaturationDis 8, @LightDis 16, @LumaDis 24, @aFactorDis 32, @bFactorDis 40
Uses eax, ebx, ecx, esi, edi, edx
mov D@iCounter 0
mov D@MaxCount2 0
mov ebx D@ImgWidth
imul ebx D@ImgHeight
mov D@MaxCount ebx
finit
mov esi D@pColorData
.While D@iCounter < ebx
lea ebx D@Red | movzx edi B$esi+RGBTRIPLE.rgbtRedDis | mov D$ebx edi
lea edx D@Green | movzx edi B$esi+RGBTRIPLE.rgbtGreenDis | mov D$edx edi
lea ecx D@Blue | movzx edi B$esi+RGBTRIPLE.rgbtBlueDis | mov D$ecx edi
lea edi D@MyPixelSrc | mov D$edi 0
mov eax D@Red | mov B$edi+ARGB.RedDis al
mov eax D@Green | mov B$edi+ARGB.GreenDis al
mov eax D@Blue | mov B$edi+ARGB.BlueDis al
lea ebx D@HueDis | mov D$ebx 0 | mov D$ebx+4 0
lea edx D@SaturationDis | mov D$edx 0 | mov D$edx+4 0
lea ecx D@LightDis | mov D$ecx 0 | mov D$ecx+4 0
call RGBtoHSL edi, ebx, edx, ecx
...If eax <> 0 ; do not compute gray color
lea ebx D@LumaDis | mov D$ebx 0 | mov D$ebx+4 0
lea edx D@aFactorDis | mov D$edx 0 | mov D$edx+4 0
lea ecx D@bFactorDis | mov D$ecx 0 | mov D$ecx+4 0
call RGBtoCieLab D@Red, D@Green, D@Blue, ebx, edx, ecx
fld R$CieLabMean.Light | fadd R$ebx | fstp R$CieLabMean.Light
fld R$CieLabMean.aFactor | fadd R$edx | fstp R$CieLabMean.aFactor
fld R$CieLabMean.bFactor | fadd R$ecx | fstp R$CieLabMean.bFactor
;fld R$CieLabMean.bFactor | fdiv R$CieLabMean.aFactor | fadd R$CieLabMean.KFactor | fstp R$CieLabMean.KFactor
inc D@MaxCount2
...End_If
add esi 3
inc D@iCounter
mov ebx D@MaxCount
.End_While
fld R$CieLabMean.Light | fidiv F@MaxCount2 | fstp R$CieLabMean.Light
fld R$CieLabMean.aFactor | fidiv F@MaxCount2 | fstp R$CieLabMean.aFactor
fld R$CieLabMean.bFactor | fidiv F@MaxCount2 | fstp R$CieLabMean.bFactor
; fld R$CieLabMean.KFactor | fidiv F@MaxCount2 | fstp R$CieLabMean.KFactor
EndP
Proc CieLabGetVariance:
Arguments @pColorData, @pMean, @ImgWidth, @ImgHeight
Local @iCounter, @Red, @Green, @Blue, @Y, @MaxCount, @MyPixelSrc, @MaxCount2
Structure @TempStorage 44, @HueDis 0, @SaturationDis 8, @LightDis 16, @LumaDis 24, @aFactorDis 32, @bFactorDis 40
Uses eax, ebx, ecx, esi, edi, edx
finit
mov D@iCounter 0
mov D@MaxCount2 0
mov ebx D@ImgWidth
imul ebx D@ImgHeight
mov D@MaxCount ebx
mov esi D@pColorData
.While D@iCounter < ebx
lea ebx D@Red | movzx edi B$esi+RGBTRIPLE.rgbtRedDis | mov D$ebx edi
lea edx D@Green | movzx edi B$esi+RGBTRIPLE.rgbtGreenDis | mov D$edx edi
lea ecx D@Blue | movzx edi B$esi+RGBTRIPLE.rgbtBlueDis | mov D$ecx edi
lea edi D@MyPixelSrc | mov D$edi 0
mov eax D@Red | mov B$edi+ARGB.RedDis al
mov eax D@Green | mov B$edi+ARGB.GreenDis al
mov eax D@Blue | mov B$edi+ARGB.BlueDis al
lea ebx D@HueDis | mov D$ebx 0 | mov D$ebx+4 0
lea edx D@SaturationDis | mov D$edx 0 | mov D$edx+4 0
lea ecx D@LightDis | mov D$ecx 0 | mov D$ecx+4 0
call RGBtoHSL edi, ebx, edx, ecx
...If eax <> 0 ; do not compute gray color
lea ebx D@LumaDis | mov D$ebx 0 | mov D$ebx+4 0
lea edx D@aFactorDis | mov D$edx 0 | mov D$edx+4 0
lea ecx D@bFactorDis | mov D$ecx 0 | mov D$ecx+4 0
call RGBtoCieLab D@Red, D@Green, D@Blue, ebx, edx, ecx
fld R$CieLabMean.Light | fsub R$ebx | fabs | fmul ST0 | fadd R$CieLabVariance.Light | fstp R$CieLabVariance.Light
fld R$CieLabMean.aFactor | fsub R$edx | fabs | fmul ST0 | fadd R$CieLabVariance.aFactor | fstp R$CieLabVariance.aFactor
fld R$CieLabMean.bFactor | fsub R$ecx | fabs | fmul ST0 | fadd R$CieLabVariance.bFactor | fstp R$CieLabVariance.bFactor
;fdiv R$Variance.Saturation | fld R$Mean.KFactor | fsub ST1 | fabs | fmul ST0 | fadd R$Variance.KFactor | fstp R$Variance.KFactor
inc D@MaxCount2
...End_If
add esi 3
inc D@iCounter
mov ebx D@MaxCount
.End_While
fld R$CieLabVariance.Light | fidiv F@MaxCount2 | fstp R$CieLabVariance.Light
fld R$CieLabVariance.aFactor | fidiv F@MaxCount2 | fstp R$CieLabVariance.aFactor
fld R$CieLabVariance.bFactor | fidiv F@MaxCount2 | fstp R$CieLabVariance.bFactor
EndP
The GetCieLabStandardDeviation does not compute gray values. I´ll later make this as a variable and also make another variable to work with colors schemes different then D65, observer 2, such as D55, D50, observer 10 etc.
For now, i´m just testing the standard deviation and see how to implement it as the ones in the pdf with the weight and other variables.
Note: a few variables names are incorrect, cause i didn´t had time to fix that yet. Since i was trying to make it work the std dev i let some variables there even if they are unused.
If it gets really mathematical, you can check with either GSL (http://www.webalice.it/jj2006/MasmBasicQuickReference.htm#Mb1123) or YEPPP! (http://masm32.com/board/index.php?topic=2445.msg25742#msg25742)...
the RosAsm syntax looks a bit strange :P
If you found out how, try port to masm and will try to assemble it .
I´m currently trying to fix a RGBtoCielab/CieLabtoRGB functions, because it seems that there are some inconsistencies in those colorspaces.
I suceeded to convert the color spaces with http://www.easyrgb.com/index.php?X=MATH&H=01#text1, but....the resultant image losts quality due o gamma error i suppose. I´ll see later what is going on after i try this other code below:
http://www.bastijn.nl/archives/153
About the syntax....mainly this is the macro set i use.
The B$ = byte ptr
D$ = dword ptr
W$ word ptr
@ = local variable
while/end_while macros same as in masm
If/..If...same as in masm
[CieLabStdDev:
CieLabStdDev.Light: R$ 0
CieLabStdDev.aFactor: R$ 0
CieLabStdDev.bFactor: R$ 0
CieLabStdDev.KFactor: R$ 0]
Global structure where each member has 8 bytes (Fpu Real)
Here are some preliminary results from both algos of RBGtoCielab
From easyRGB site
(http://i42.tinypic.com/14cuohk.jpg)
From www.bastijn.nl (http://www.bastijn.nl) site
(http://i44.tinypic.com/35jmh3m.jpg)
Although bastin site looks way better....I just converted half of the function. I had no time to finish the CieLabtoRGB of it, so i used the one in EasyRGB. On this image it was ok, but on several others, there are showing artifacts and gamma errors (shows red, green, yellow, orange pixels)
I´ll fully convert it tonight an see what is the result.
If i suceed to convert it, then i can use the standard deviation etc, once dedndave suceed to translate it.
Hi,
Following that link gets me to an *.EXE, not a *.PDF. Is
there another link?
I have a book that mentions the L-a-b (or L*a*b*) color
coordinate system, but just gives a formula for the coord-
inate transformation and a description.
Regards,
Steve
hi Steve
well - the 4shared page has about 20 download buttons on it - lol
and when you find the right one - you have to sign in to get it
maybe Christian Graus can help with the colors...
this is part 6 of a 6-part series
http://www.codeproject.com/Articles/7138/Image-Processing-for-Dummies-with-C-and-GDI-Part-6 (http://www.codeproject.com/Articles/7138/Image-Processing-for-Dummies-with-C-and-GDI-Part-6)
his other articles are listed here
http://www.codeproject.com/Articles/Christian-Graus#articles (http://www.codeproject.com/Articles/Christian-Graus#articles)
Hi Steve
a exe ? Are u sure ? The link is in my 1st post
it is in 4shared here
http://search.4shared.com/postDownload/sVGa3s3X/p66-huang.html
It is a rar file that inside contains the pdf
The formula is what i´m trying to understand. I suceeded to convert some color functions on the easyrgb site, but this last one from them is too slow and also innacurate. I`m trying to convert the 2nd example. The results so far are somewhat similar to a IPT colorspace, except that they don´t show so much details when the image is too dark.
What i´m trying to understand and create is the formulas described in the chapter
3. AUTOMATIC SELECTIVE COLOR TRANSFER ALGORITHM FOR IMAGES
3.1 New mean and standard deviation values of ASCT algorithm
page 2 of the pdf i uploaded
These formulas:
(http://i42.tinypic.com/jhucdx.jpg)
I don´t know what they means so i can try to code them.
guga,
dedndave,
did you have the rights to share that paper?
Nope, this article is on internet, but, it is not mine. The article was released by the authors on some color related websites for free.
It is not from a book or something.
Btw...the article is not commercial. As far i remember it is a study from students from a university related to color transfer techniques.
QuotePermission to make digital or hard copies of all or part of this work for
personal or classroom use is granted without fee provided that copies are
not made or distributed for profit or commercial advantage and that
copies bear this notice and the full citation on the first page. To copy
otherwise, or republish, to post on servers or to redistribute to lists,
requires prior specific permission and/or a fee.
SAC'11, March 21-25, 2011, TaiChung, Taiwan.
Copyright 2011 ACM 978-1-4503-0113-8/11/03...$10.00
Yeah, like i said, it is for free as long you don´t use for commercial purposes. But the copy or post the whole pages (or the book, that contains this article) requires permission.
The article is at page 66, therefore it is not the whole "book" and neither for commercial purposes, so using a few pages (6) for study and educational is granted.
This is related to the whole book that seems to be released articles from several people on a symposium.
Look at google and you will see this article in hundreds of universities sites with links etc
https://www.google.com.br/search?q=Copyright+2011+ACM+978-1-4503-0113-8/11/03%E2%80%A6%2410.00.&ie=utf-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&gws_rd=cr&ei=7YBmUtPZNsOrkQeqsYHABA#psj=1&q=ACM+978-1-4503-0113-8%2F11%2F03&rls=org.mozilla:en-US%3Aofficial&safe=off
What is not allowed is copy the whole book of this Symposhium and share it. But isolated articles for study and educational purposes this is ok.
I´m not sure if this Yao-Hsien Huang is the same guy that send me trough email his app that is able to unblur images that will be releases on Adobe CS, but definitelly, reproducing and article for this purposes and situation is legal.
Your argumentation makes not much sense, because the Article can be download from the ACM digital library (copyright holder) for 10$ (15$ for non members). Educational (or private) purposes implies that the paper is only shared within the study group and not the WWW.
Your google result only shows references to that paper.
You might ask Hutch what he thinks on that or simply type out the formulas and correctly quote the text!
Quote from: dedndave on October 23, 2013, 12:04:56 AM
hi Steve
well - the 4shared page has about 20 download buttons on it - lol
and when you find the right one - you have to sign in to get it
Hi Dave,
Right. That explains what happened, except for the EXE
download. Thanks.
Quote
maybe Christian Graus can help with the colors...
this is part 6 of a 6-part series
http://www.codeproject.com/Articles/7138/Image-Processing-for-Dummies-with-C-and-GDI-Part-6 (http://www.codeproject.com/Articles/7138/Image-Processing-for-Dummies-with-C-and-GDI-Part-6)
That looks okay to explain the HLS color space. Lab is a
bit different.
Quote from: guga on October 23, 2013, 12:07:55 AM
What i´m trying to understand and create is the formulas described in the chapter
3. AUTOMATIC SELECTIVE COLOR TRANSFER ALGORITHM FOR IMAGES
3.1 New mean and standard deviation values of ASCT algorithm
page 2 of the pdf i uploaded
I don´t know what they means so i can try to code them.
He is applying image processing to images based on the
the statistics (mean, standard deviation) of portions of the
images. He can adjust the processing so it applies to image
regions that appear rather different. The book I have uses
something similar to sharpen images. Using the average
pixel values of a small region to lighten dark areas for instance.
And using differing amounts of sharpening based on the local
standard deviation of the pixels.
Regards,
Steve
the EXE is probably an "ilivid" downloader, custom to that specific file
i think they're safe - but i still prefer not to download and run EXE's like that :redface:
livid ? dont dl it !. 4shared have some merchandising...Only dl the rar file after the circle is runnin when you press to dl
i have tried ilivid in the past
as i recall, it was pretty easy to remove any ad-ware remnants after you get what you want
dave, i´m trying to convert this to C so it can be easy to analyse, but VisualStudio 10 is refusing to compiler....What i´m making wrong here ?
I´m trying to convert it to plain C (No c++), but VS keeps giving me errors
Original code
vec3 RGB2Lab(in vec3 rgb){
float R = rgb.x;
float G = rgb.y;
float B = rgb.z;
// threshold
float T = 0.008856;
float X = R * 0.412453 + G * 0.357580 + B * 0.180423;
float Y = R * 0.212671 + G * 0.715160 + B * 0.072169;
float Z = R * 0.019334 + G * 0.119193 + B * 0.950227;
// Normalize for D65 white point
X = X / 0.950456;
Y = Y;
Z = Z / 1.088754;
bool XT, YT, ZT;
XT = false; YT=false; ZT=false;
if(X > T) XT = true;
if(Y > T) YT = true;
if(Z > T) ZT = true;
float Y3 = pow(Y,1/3f);
float fX, fY, fZ;
if(XT){ fX = pow(X, 1/3f);} else{ fX = 7.787 * X + 16/116; }
if(YT){ fY = Y3; } else{ fY = 7.787 * Y + 16/116 ; }
if(ZT){ fZ = pow(Z,1/3f); } else{ fZ = 7.787 * Z + 16/116; }
float L; if(YT){ L = (116 * Y3) - 16.0; }else { L = 903.3 * Y; }
float a = 500 * ( fX - fY );
float b = 200 * ( fY - fZ );
return vec3(L,a,b);
}
vec3 Lab2RGB(in vec3 lab){
//Thresholds
float T1 = 0.008856;
float T2 = 0.206893;
float X,Y,Z;
//Compute Y
bool XT, YT, ZT;
XT = false; YT=false; ZT=false;
float fY = pow(((lab.x + 16.0) / 116.0),3);
if(fY > T1){ YT = true; }
if(YT){ fY = fY; } else{ fY = (lab.x / 903.3); }
Y = fY;
//Alter fY slightly for further calculations
if(YT){ fY = pow(fY,1/3f); } else{ fY = (7.787 * fY + 16.0/116.0); }
//Compute X
float fX = ( lab.y / 500.0 ) + fY;
if(fX > T2){ XT = true; }
if(XT){ X = pow(fX,3); } else{X = ((fX - (16/116.0)) / 7.787); }
//Compute Z
float fZ = fY - ( lab.z / 200.0 );
if(fZ > T2){ ZT = true; }
if(ZT){ Z = pow(fZ,3); } else{ Z = ((fZ - (16/116.0)) / 7.787); }
//Normalize for D65 white point
X = X * 0.950456;
Z = Z * 1.088754;
//XYZ to RGB part
float R = 3.240479 * X + -1.537150 * Y + -0.498535 * Z;
float G = -0.969256 * X + 1.875991 * Y + 0.041556 * Z;
float B = 0.055648 * X + -0.204043 * Y + 1.057311 * Z;
return vec3(R,G,B);
}
Mine code:
struct lab{
float x;
float y;
float z;
} lab; // this is just a random name not mine!
void Lab2RGB(struct lab *lab){
//Thresholds
float T1 = 0.008856;
float T2 = 0.206893;
float X,Y,Z;
//Compute Y
bool XT, YT, ZT;
XT = false; YT=false; ZT=false;
float fY = pow(((lab.x + 16.0) / 116.0),3);
if(fY > T1){ YT = true; }
if(YT){ fY = fY; } else{ fY = (lab.x / 903.3); }
Y = fY;
//Alter fY slightly for further calculations
if(YT){ fY = pow(fY,1/3f); } else{ fY = (7.787 * fY + 16.0/116.0); }
//Compute X
float fX = ( lab.y / 500.0 ) + fY;
if(fX > T2){ XT = true; }
if(XT){ X = pow(fX,3); } else{X = ((fX - (16/116.0)) / 7.787); }
//Compute Z
float fZ = fY - ( lab.z / 200.0 );
if(fZ > T2){ ZT = true; }
if(ZT){ Z = pow(fZ,3); } else{ Z = ((fZ - (16/116.0)) / 7.787); }
//Normalize for D65 white point
X = X * 0.950456;
Z = Z * 1.088754;
//XYZ to RGB part
float R = 3.240479 * X + -1.537150 * Y + -0.498535 * Z;
float G = -0.969256 * X + 1.875991 * Y + 0.041556 * Z;
float B = 0.055648 * X + -0.204043 * Y + 1.057311 * Z;
//return vec3(R,G,B); ????????????? how to return it properly ?
}
The reason is that i suceeded (i guess) to port the RGB2Lab, but when i did the opposite function (LAb2RGB) the image turns onto Green !
Can someone port this functions to VS or masm, so i can analyse them to see how they works ?
try this:
// TestRGB2Lab.c for msvc
#include <stdio.h>
//#include <stdbool.h>
#include <math.h>
typedef int bool;
#define true 1
#define false 0
typedef struct _VEC3
{
float x,y,z;
} VEC3, *PVEC3;
VEC3 RGB2Lab(VEC3 rgb)
{
VEC3 rv3;
float R = rgb.x;
float G = rgb.y;
float B = rgb.z;
// threshold
float T = 0.008856;
float X = R * 0.412453 + G * 0.357580 + B * 0.180423;
float Y = R * 0.212671 + G * 0.715160 + B * 0.072169;
float Z = R * 0.019334 + G * 0.119193 + B * 0.950227;
bool XT, YT, ZT;
float fX, fY, fZ;
float Y3;
float L;
float a, b;
// Normalize for D65 white point
X = X / 0.950456;
//Y = Y;
Z = Z / 1.088754;
if (X > T) XT = true; else XT = false;
if (Y > T) YT = true; else YT = false;
if (Z > T) ZT = true; else ZT = false;
Y3 = pow(Y, 1 / 3.0);
if (XT) {
fX = pow(X, 1 / 3.0);
} else {
fX = 7.787 * X + 16 / 116;
}
if (YT) {
fY = Y3;
} else {
fY = 7.787 * Y + 16 / 116;
}
if (ZT) {
fZ = pow(Z, 1 / 3.0);
} else {
fZ = 7.787 * Z + 16 / 116;
}
if (YT) {
L = (116 * Y3) - 16.0;
} else {
L = 903.3 * Y;
}
a = 500 * (fX - fY);
b = 200 * (fY - fZ);
//return vec3(L, a, b);
rv3.x = L;
rv3.y = a;
rv3.z = b;
return rv3;
}
VEC3 Lab2RGB(VEC3 lab)
{
VEC3 rv3;
//Thresholds
float T1 = 0.008856;
float T2 = 0.206893;
float X, Y, Z;
float fX, fY, fZ;
float R, G, B;
//Compute Y
bool XT, YT, ZT;
XT = false;
YT = false;
ZT = false;
fY = pow(((lab.x + 16.0) / 116.0), 3);
if (fY > T1) {
YT = true;
}
if (YT) {
fY = fY;
} else {
fY = (lab.x / 903.3);
}
Y = fY;
//Alter fY slightly for further calculations
if (YT) {
fY = pow(fY, 1 / 3.0);
} else {
fY = (7.787 * fY + 16.0 / 116.0);
}
//Compute X
fX = (lab.y / 500.0) + fY;
if (fX > T2) {
XT = true;
}
if (XT) {
X = pow(fX, 3);
} else {
X = ((fX - (16 / 116.0)) / 7.787);
}
//Compute Z
fZ = fY - (lab.z / 200.0);
if (fZ > T2) {
ZT = true;
}
if (ZT) {
Z = pow(fZ, 3);
} else {
Z = ((fZ - (16 / 116.0)) / 7.787);
}
//Normalize for D65 white point
X = X * 0.950456;
Z = Z * 1.088754;
//XYZ to RGB part
R = 3.240479 * X + -1.537150 * Y + -0.498535 * Z;
G = -0.969256 * X + 1.875991 * Y + 0.041556 * Z;
B = 0.055648 * X + -0.204043 * Y + 1.057311 * Z;
rv3.x = R;
rv3.y = G;
rv3.z = B;
return rv3;
//return vec3(R, G, B);
}
int main(int argc, char **argv)
{
VEC3 v3;
v3.x = 50.0;
v3.y = 50.0;
v3.z = 50.0;
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = Lab2RGB(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = RGB2Lab(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
return 0;
}Can anyone try this version with MSVS 2013 in C mode (C99)?
With PellesC one can compile it. // RGB2LabTest.c for C99
#include <stdio.h>
#include <stdbool.h>
#include <math.h>
typedef struct _VEC3
{
float x,y,z;
} VEC3, *pvec3;
VEC3 RGB2Lab(VEC3 rgb)
{
VEC3 rv3;
float R = rgb.x;
float G = rgb.y;
float B = rgb.z;
// threshold
float T = 0.008856;
float X = R * 0.412453 + G * 0.357580 + B * 0.180423;
float Y = R * 0.212671 + G * 0.715160 + B * 0.072169;
float Z = R * 0.019334 + G * 0.119193 + B * 0.950227;
// Normalize for D65 white point
X = X / 0.950456;
//Y = Y;
Z = Z / 1.088754;
bool XT, YT, ZT;
if (X > T) XT = true; else XT = false;
if (Y > T) YT = true; else YT = false;
if (Z > T) ZT = true; else ZT = false;
float Y3 = pow(Y, 1 / 3.0);
float fX, fY, fZ;
if (XT) {
fX = pow(X, 1 / 3.0);
} else {
fX = 7.787 * X + 16 / 116;
}
if (YT) {
fY = Y3;
} else {
fY = 7.787 * Y + 16 / 116;
}
if (ZT) {
fZ = pow(Z, 1 / 3.0);
} else {
fZ = 7.787 * Z + 16 / 116;
}
float L;
if (YT) {
L = (116 * Y3) - 16.0;
} else {
L = 903.3 * Y;
}
float a = 500 * (fX - fY);
float b = 200 * (fY - fZ);
//return vec3(L, a, b);
rv3.x = L;
rv3.y = a;
rv3.z = b;
return rv3;
}
VEC3 Lab2RGB(VEC3 lab)
{
VEC3 rv3;
//Thresholds
float T1 = 0.008856;
float T2 = 0.206893;
float X, Y, Z;
//Compute Y
bool XT, YT, ZT;
XT = false;
YT = false;
ZT = false;
float fY = pow(((lab.x + 16.0) / 116.0), 3);
if (fY > T1) {
YT = true;
}
if (YT) {
fY = fY;
} else {
fY = (lab.x / 903.3);
}
Y = fY;
//Alter fY slightly for further calculations
if (YT) {
fY = pow(fY, 1 / 3.0);
} else {
fY = (7.787 * fY + 16.0 / 116.0);
}
//Compute X
float fX = (lab.y / 500.0) + fY;
if (fX > T2) {
XT = true;
}
if (XT) {
X = pow(fX, 3);
} else {
X = ((fX - (16 / 116.0)) / 7.787);
}
//Compute Z
float fZ = fY - (lab.z / 200.0);
if (fZ > T2) {
ZT = true;
}
if (ZT) {
Z = pow(fZ, 3);
} else {
Z = ((fZ - (16 / 116.0)) / 7.787);
}
//Normalize for D65 white point
X = X * 0.950456;
Z = Z * 1.088754;
//XYZ to RGB part
float R = 3.240479 * X + -1.537150 * Y + -0.498535 * Z;
float G = -0.969256 * X + 1.875991 * Y + 0.041556 * Z;
float B = 0.055648 * X + -0.204043 * Y + 1.057311 * Z;
rv3.x = R;
rv3.y = G;
rv3.z = B;
return rv3;
//return vec3(R, G, B);
}
int main(int argc, char **argv)
{
VEC3 v3;
v3.x = 50.0;
v3.y = 50.0;
v3.z = 50.0;
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = Lab2RGB(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = RGB2Lab(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
return 0;
}
Tks twell
I compiled it for console mode and it works on VS2008. I just needed to change the pow function to powf due to ambiguity found.
// ColorTestConvert.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
/*
int _tmain(int argc, _TCHAR* argv[])
{
return 0;
}
*/
// RGB2LabTest.c for C99
#include <stdio.h>
//#include <stdbool.h>
#include <math.h>
typedef struct _VEC3
{
float x,y,z;
} VEC3, *pvec3;
VEC3 RGB2Lab(VEC3 rgb)
{
VEC3 rv3;
float R = rgb.x;
float G = rgb.y;
float B = rgb.z;
// threshold
float T = 0.008856;
float X = R * 0.412453 + G * 0.357580 + B * 0.180423;
float Y = R * 0.212671 + G * 0.715160 + B * 0.072169;
float Z = R * 0.019334 + G * 0.119193 + B * 0.950227;
// Normalize for D65 white point
X = X / 0.950456;
//Y = Y;
Z = Z / 1.088754;
bool XT, YT, ZT;
if (X > T) XT = true; else XT = false;
if (Y > T) YT = true; else YT = false;
if (Z > T) ZT = true; else ZT = false;
float Y3 = powf(Y, 1 / 3.0);
float fX, fY, fZ;
if (XT) {
fX = powf(X, 1 / 3.0);
} else {
fX = 7.787 * X + 16 / 116;
}
if (YT) {
fY = Y3;
} else {
fY = 7.787 * Y + 16 / 116;
}
if (ZT) {
fZ = powf(Z, 1 / 3.0);
} else {
fZ = 7.787 * Z + 16 / 116;
}
float L;
if (YT) {
L = (116 * Y3) - 16.0;
} else {
L = 903.3 * Y;
}
float a = 500 * (fX - fY);
float b = 200 * (fY - fZ);
//return vec3(L, a, b);
rv3.x = L;
rv3.y = a;
rv3.z = b;
return rv3;
}
VEC3 Lab2RGB(VEC3 lab)
{
VEC3 rv3;
//Thresholds
float T1 = 0.008856;
float T2 = 0.206893;
float X, Y, Z;
//Compute Y
bool XT, YT, ZT;
XT = false;
YT = false;
ZT = false;
float fY = pow(((lab.x + 16.0) / 116.0), 3);
if (fY > T1) {
YT = true;
}
if (YT) {
fY = fY;
} else {
fY = (lab.x / 903.3);
}
Y = fY;
//Alter fY slightly for further calculations
if (YT) {
fY = powf(fY, 1 / 3.0);
} else {
fY = (7.787 * fY + 16.0 / 116.0);
}
//Compute X
float fX = (lab.y / 500.0) + fY;
if (fX > T2) {
XT = true;
}
if (XT) {
X = pow(fX, 3);
} else {
X = ((fX - (16 / 116.0)) / 7.787);
}
//Compute Z
float fZ = fY - (lab.z / 200.0);
if (fZ > T2) {
ZT = true;
}
if (ZT) {
Z = pow(fZ, 3);
} else {
Z = ((fZ - (16 / 116.0)) / 7.787);
}
//Normalize for D65 white point
X = X * 0.950456;
Z = Z * 1.088754;
//XYZ to RGB part
float R = 3.240479 * X + -1.537150 * Y + -0.498535 * Z;
float G = -0.969256 * X + 1.875991 * Y + 0.041556 * Z;
float B = 0.055648 * X + -0.204043 * Y + 1.057311 * Z;
rv3.x = R;
rv3.y = G;
rv3.z = B;
return rv3;
//return vec3(R, G, B);
}
int main(int argc, char **argv)
{
VEC3 v3;
v3.x = 50.0;
v3.y = 50.0;
v3.z = 50.0;
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = Lab2RGB(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
v3 = RGB2Lab(v3); // pass copy of v3
printf("x= %0.3f, y= %0.3f, z= %0.3f\n", v3.x, v3.y, v3.z);
return 0;
}
Ok, guys...both functions are fully working (RGB2Lab and Lab2RGB)
What was missing on the original code is a division of the Red, Green and Blue with 255
I´ll make some other tests and try to implement other matrices for HDTV etc before release them here
Now, it is needed to understand the other functions related to the article posted.