I'm facing a problem while trying to convert a colored image to grey scale image using C++. I think there's a problem in the use of function GetRGB().
Here is the source code and related header file.
void CCorner::RGBToGrayScale(CImage* pIn, CImage* pOut)
{
//
// INPUT:
// CImage* pIn: The input image with 24bit depth
//
// OUTPUT:
// CImage* pOut: The output image. It has ALREADY been initialized
// with the same dimension as the input image (pIN) and
// formatted to 8bit depth (256 gray levels).
//
int height = pIn->GetHeight();
int width = pIn->GetWidth();
int clrOriginal=pIn->GetColorType();
if (height && width){
for(int i=0;i<height;i++){
for(int j=0;j<width;j++){
byte *r,*g,*b;
r=NULL; g=NULL; b=NULL;
bool colors=pIn->GetRGB(i,j,r,g,b);
double newindex = 0.299**r+0.587**g+0.114**b;
pOut->SetIndex(i,j,newindex);
}
}
}
}
While GetRGB() is defined as
virtual BOOL GetRGB(int x, int y, byte* r, byte* g, byte* b)
{ return implementation->GetRGB(x, y, r, g, b); }
Thanks for helping!
GetRGB
is expecting you to provide pointers to actual byte
s where it will output the results for r
, g
and b
. This is a way of returning multiple results from a function in C++, by using output parameters.
However, you're giving it pointers to NULL
here:
byte *r,*g,*b;
r=NULL; g=NULL; b=NULL;
So there's nowhere to write the results. When you dereference them later (via *r
, *g
, *b
) you'll get undefined behaviour because they're null
.
What you should be doing, is this:
byte r, g, b;
bool colors = pIn->GetRGB(i, j, &r, &g, &b);
And naturally, no need to deference them later because they're not pointers:
double newindex = 0.299*r+0.587*g+0.114*b;
You are passing null pointers to a function that expects to write to those memory addresses. Give it valid memory addresses where it can store the result for you.
byte r = 0, g = 0, b = 0;
bool colors = pIn->GetRGB(i, j, &r, &g, &b);
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