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Hi all,
I have to make a library to convert the Color from Lab value to RGB value. However, I have no much idea on the calculations or algorithms.
Suppose I will receive a data (Char pointer) then convert to RGB.
Can some of you give me some hints or examples? Please Please...
I believed that this should be easy for some experts.
Thanks for your help..
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azusakt wrote: I have no much idea on the calculations or algorithms.
You don't have much idea or you have absolutely no idea? Tell us what you've tried.
Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP
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Actually, I'm a beginner in writting Graphic related program. especially in C++.
I have no idea on the calculation for processing & converting the LAB to RGB. So I hope to find some examples with codings that I can easily to learn and understand .
Could you provide me some program examples if you have this experience.
Thanks a lot.
modified on Tuesday, January 29, 2008 10:04:23 PM
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azusakt wrote: I have to make a library to convert the Color from Lab value to RGB value. However, I have no much idea on the calculations or algorithms.
But documentation exists http://en.wikipedia.org/wiki/Lab_color_space#Advantages_of_Lab[^].
There is also the very nice Guillaume Leparmentier's article [^] here at CP.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
[my articles]
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I guess, by using an array structure you can do this. For Example:
<br />
static COLORREF arColors[] = {<br />
RGB(0,255,0),<br />
RGB(0,255,255)<br />
};<br />
<br />
char* arNames[] = {<br />
"green",<br />
"cyan"<br />
};<br />
<br />
for(int i=0; i<2; i++)<br />
{<br />
arColors[i] = i;
arNames[i] = atof(i);<br />
}<br />
modified on Wednesday, January 30, 2008 4:09:09 AM
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Thanks for you reply.
Can you provide me a sample code for converting Lab value to RGB value?
I've read some documents, they said the step should
1. convert Lab -> XYZ
2. convert XYZ -> RGB
I don't know how to write such calculations.
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This is a constant RGB macros of the COLORREF structure. Anyway, from 0 to 255 numeric values are equivalence a 24-Bit COLORREF's scope. If you want to chance only RGB macros, you can use the
typedef struct tagCOLORREF structure.
Forexample:
<br />
#define XYZ(int i1, int i2, int i3) 0<br />
<br />
int* pNewInt = new int[255];<br />
pNewInt = NULL;<br />
#ifdef COLORREF<br />
for(int i=0; i<255; i++)<br />
{<br />
RGB(pNewInt[i],pNewInt[i],pNewInt[i]) = XYZ(pNewInt[i],pNewInt[i],pNewInt[i]);<br />
}<br />
delete []pNewInt;<br />
#endif
That is must be a defined tagpoint struct what own yourself.
modified on Thursday, January 31, 2008 6:05:14 AM
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Dear friends,
I am opening the selected printer's document property dialog from my application.
I am using the following code
PRINTER_DEFAULTS PrinterDef = {NULL, NULL, PRINTER_ALL_ACCESS};
HANDLE hPrinter;
PDEVMODEW pDevmode = NULL;
if(OpenPrinter(PRINTER_NAME, &hPrinter, &PrinterDef))
{
int nSize = DocumentProperties(this->m_hWnd, hPrinter,
PRINTER_NAME, NULL, NULL, 0);
pDevmode = (PDEVMODEW)LocalAlloc(LPTR, nSize);
DocumentProperties(this->m_hWnd, hPrinter, PRINTER_NAME,
pDevmode, NULL, DM_IN_PROMPT );
ClosePrinter(hPrinter);
}
Now I want to cature the paper size changes made by the user on document property dialog.
Please Help.
Sandip
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Check out these two code paths:
float s = 1.0f + pow(2.0f,-8.0f) + pow(2.0f,-18.0f);
float fRes1 = 1024 * s;
float fRes2 = 0.0f;
for(int i=0; i<1024; ++i)
fRes2 +=s;
now watch the results:
fRes1: 1028.0039
fRes2: 1028.0002
This was tested on Intel Dual-core, VS2005. the direct multiplication was compiled to use fmul, the accumulation was compiled to use fadd. The scalar value s was crafted to know analytically which is the correct result. it is fRes1 (the fmul result).
Can anyone shed some light on the source of the difference??
it can't be (i think) a direct precision issue - all arguments and intermediate values are *exactly* representable in single precision.
any insight would be greatly appreciated!
-Ofek
modified 23-Jan-21 21:03pm.
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It's of float issue. Using double instead will solve this.
Maxwell Chen
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OfekSH wrote: it can't be (i think) a direct precision issue
I think the opposite.
OfekSH wrote: all arguments and intermediate values are *exactly* representable in single precision.
for instance, when executing s*1023 + s sum, you cannot line up the addition arguments without precision loss.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
[my articles]
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I replaced all occurrences of float with double, and removed all the tail f, then the results match.
Maxwell Chen
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Maxwell Chen wrote: I replaced all occurrences of float with double, and removed all the tail f, then the results match.
Of course, because you're cheating!
double numbers have a 52 bit mantissa (float have a 23 bit one) and, for instance, OP's s*1023 and s numbers can be comfortably lined up for addition without precision loss.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
[my articles]
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Maxwell - thanks for your reply!
what do you mean by 'results match'? match mine, or match each other?
i already tried going double, and still got different results:
double d = 1.0 + pow(2.0,-8.0) + pow(2.0,-18.0);
double dRes1 = 1024 * d;
double dRes2 = 0.0;
for(int i=0; i<1024; ++i)
dRes2 +=d;
on my machine gives:
dRes1= 1028.0039062500000
dRes2= 1028.0002441406250
which didn't even budge the difference down.
do you get different results? on what machine/compiler?
modified 23-Jan-21 21:03pm.
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My result:
dRes1 = 1028.003906250000000
dRes2 = 1028.003906250000000
Visual C++ 2005,
Intel Centrino Core 2 Duo, T2400
Maxwell Chen
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Pallini - thanks, you're right of course, but i suspect there's more to it. going double didn't make any difference (see my post to Maxwell below).
modified 23-Jan-21 21:03pm.
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I tried and got, like Maxwell Chen, the same result (1028.0039062500000) for both dRes1 and dRes2.
I'm using VC++ 2005 on Windows XP.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
[my articles]
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Sorry for the delay - just returned from lunch. Upon further investigation, the difference is between debug and release builds. Debug build compiles to fpu code:
00C1A579 fldz
00C1A57B fstp qword ptr [ebp-48h]
00C1A57E mov dword ptr [i],0
00C1A585 jmp CurrentFunction+0C0h (0C1A590h)
00C1A587 mov eax,dword ptr [i]
00C1A58A add eax,1
00C1A58D mov dword ptr [i],eax
00C1A590 cmp dword ptr [i],400h
00C1A597 jge CurrentFunction+0D4h (0C1A5A4h)
00C1A599 fld qword ptr [ebp-48h]
00C1A59C fadd qword ptr [ebp-28h]
00C1A59F fstp qword ptr [ebp-48h]
00C1A5A2 jmp CurrentFunction+0B7h (0C1A587h)
which gives the wrong result, while release builds SSE code (along with loop unrolling):
004CAB82 xorps xmm1,xmm1
004CAB85 mov eax,80h
004CAB8A lea ebx,[ebx]
004CAB90 sub eax,1
004CAB93 addsd xmm1,xmm0
004CAB97 addsd xmm1,xmm0
004CAB9B addsd xmm1,xmm0
004CAB9F addsd xmm1,xmm0
004CABA3 addsd xmm1,xmm0
004CABA7 addsd xmm1,xmm0
004CABAB addsd xmm1,xmm0
004CABAF addsd xmm1,xmm0
004CABB3 jne CurrentFunction+80h (4CAB90h)
004CABB5 movsd mmword ptr [esp+38h],xmm1
which gives an accurate result.
setting the FPU control word to double or extended double precision solved it - i guess either your FPU control word was already set right, or you tested it in release builds.
thanks for everyone's time!
modified 23-Jan-21 21:03pm.
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I tested in debug build.
Maxwell Chen
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The project created earlier a Direct3D device. Apparently [^] this changes by default the FPU precision to single.
Haven't decided yet whether to change creation params to use D3DCREATE_FPU_PRESERVE, or to surround the code where i (think i) need extra precision with manual precision set/restore. Either way - problem found.
Thanks everyone!
modified 23-Jan-21 21:03pm.
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I want to set a timer to execute in every two minutes in visual C++. Please help
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If you are using MFC, you can use CWnd::SetTimer[^]
BTW, don't forget your friend google...
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::SetTimer(1, 120000, MyTest);
void CALLBACK MyTest(HWND hW, UINT msg, UINT ev, DWORD time) {
}
Maxwell Chen
modified on Tuesday, January 29, 2008 10:35:27 AM
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Maxwell Chen wrote: ::SetTimer(1, 120, MyTest);
Perhaps you meant to use 120000 instead. 
"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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DavidCrow wrote: Perhaps you meant to use 120000 instead.
Yes.
Maxwell Chen
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