Pointer Problem

[dingyong198608]

Could you check the error, please?
I find the problem, the problem is the pointer problem for (*rdatap)[i][j]
Anyone can tell me why and how to solve this?

The problem is the evaluation from matrix to pointer. The values are changed.
Example:
-----the 0 row---0----colomn---
R=253 G=253 B=253

changed to
-----the 0 row---0----colomn---
R=253 G=12 B=12

This is a simple C++ program to read the data from RGB image, and then output the image into another file without any processing. For this image, the R, G, B values are equal to render the image gray scale.But the result is that they are not equal
Through debug, I find that the problem is in main() after the call of the function ::matrix2Pointer(),

Thank you for your reading and help!

Also, I find that the evaluation changed the value of (*gdatap)[0][0] into 12 when it execute the sentence (*gdatap)[192][0] = ImageData[192][0][1].

In addition, I find the latter evaluation begins to change the previous values after the row 165, from row 166

#define X_SIZE 272
#define Y_SIZE 173
#define BYTESPERPIXEL 3

#include "FileFuncRGB.h"

using namespace std;

int main()
{
	char *s;

	int **rdata;
	int **gdata;
	int **bdata;


	unsigned char imagedata[X_SIZE][Y_SIZE][BYTESPERPIXEL];


	s ="images/pcb.raw";

	readMatrix(imagedata, s);
	matrix2Pointer(imagedata, &rdata, &gdata, &bdata);

	/*for(int i =0;i<X_SIZE; i++){
		for(int j =0; j<Y_SIZE; j++){
			imagedata[i][j][0] = 0;
			imagedata[i][j][1] = 0;
			imagedata[i][j][2] = 0;
			cout<<rdata[i][j]<<" "<<gdata[i][j]<<" "<<bdata[i][j]<<endl;
		}
		cout<<endl;
	}*/

	s = "images/pcb_out_1.raw";

	pointer2Matrix(imagedata, rdata, gdata, bdata);
	writeMatrix(imagedata, s);


	return 0;
}

#ifndef FILEFUNCRGB_H_
#define FILEFUNCRGB_H_


#ifdef X_SIZE
#ifdef Y_SIZE
#ifdef BYTESPERPIXEL

#include <iostream>
#include <stdio.h>
#include "../src/def.h"

using namespace std;

void readMatrix(unsigned char ImageData[X_SIZE][Y_SIZE][BYTESPERPIXEL], char *filename){
	FILE *file;
	file=fopen(filename,"rb");
	cout<<"----------reach the file "<<filename<<" fopen------------"<<endl;

	// Read image (filename specified by first argument) into image data matrix
	if (file==NULL) {
		cout << "Cannot open file: "<<filename <<endl;
		exit(1);
	}
	fread(ImageData, sizeof(unsigned char), (X_SIZE)*(Y_SIZE)*(BYTESPERPIXEL), file);
	fclose(file);

	cout<<"----------file open is over ------------"<<endl;
}

void matrix2Pointer(unsigned char ImageData[X_SIZE][Y_SIZE][BYTESPERPIXEL], int ***rdatap,
		int ***gdatap, int ***bdatap){

	(*rdatap)= new int *[Y_SIZE];
	(*gdatap)= new int *[Y_SIZE];
	(*bdatap)= new int *[Y_SIZE];


	for(int i=0;i<X_SIZE;i++){
		(*rdatap)[i] = new int[Y_SIZE];
		(*gdatap)[i] = new int[Y_SIZE];
		(*bdatap)[i] = new int[Y_SIZE];
	}

	for(int i=0;i<X_SIZE;i++){

		for(int j=0;j<Y_SIZE;j++){
			//cout<<"-----the "<<i<<" row---"<<j<<"----colomn---"<<endl;
			(*rdatap)[i][j] = (signed int)ImageData[i][j][0];
			(*gdatap)[i][j] = (signed int)ImageData[i][j][1];
			(*bdatap)[i][j] = (signed int)ImageData[i][j][2];
			if((*rdatap)[i][j]<0){
				(*rdatap)[i][j]=0;
			}
			if((*gdatap)[i][j]<0){
				(*gdatap)[i][j]=0;
			}
			if((*bdatap)[i][j]<0){
				(*bdatap)[i][j]=0;
			}
			if((*rdatap)[i][j]>=L_LUM){
				(*rdatap)[i][j]=L_LUM-1;
			}
			if((*gdatap)[i][j]>=L_LUM){
				(*gdatap)[i][j]=L_LUM-1;
			}
			if((*bdatap)[i][j]>=L_LUM){
				(*bdatap)[i][j]=L_LUM-1;
			}
			//cout<<(*rdatap)[i][j];
		}
		//cout<<endl;
	}
	//cout<<endl;
}

void writeMatrix(unsigned char ImageData[X_SIZE][Y_SIZE][BYTESPERPIXEL], char *filename){
	FILE *file;
	file=fopen(filename,"wb");
	cout<<"----------reach the file  "<<filename<<" fwrite------------"<<endl;

	// Read image (filename specified by first argument) into image data matrix
	if (file==NULL) {
		cout << "Cannot open file: "<<filename <<endl;
		exit(1);
	}
	fwrite(ImageData, sizeof(unsigned char), X_SIZE*Y_SIZE*BYTESPERPIXEL, file);
	fclose(file);

	cout<<"----------file write is over ------------"<<endl;
}

void pointer2Matrix(unsigned char ImageData[X_SIZE][Y_SIZE][BYTESPERPIXEL], int **rdata,
		int **gdata, int **bdata){
	for(int i=0;i<X_SIZE;i++){
		//cout<<"-----the "<<i<<" row------"<<endl;
		for(int j=0;j<Y_SIZE;j++){
			ImageData[i][j][0] = (unsigned char)rdata[i][j];
			ImageData[i][j][1] = (unsigned char)gdata[i][j];
			ImageData[i][j][2] = (unsigned char)bdata[i][j];
			//cout<<rdata[i][j]<<" "<<gdata[i][j]<<" "<<bdata[i][j]<<endl;
		}
		//cout<<endl;
	}
	//cout<<endl;
}

void deletePointer(int **rdata, int **gdata, int **bdata){
	for(int i=0;i<X_SIZE;i++){
		delete [] rdata[i];
		delete [] gdata[i];
		delete [] bdata[i];
	}
	delete [] rdata;
	delete [] gdata;
	delete [] bdata;
}

#endif
#endif
#endif

#endif /* FILEFUNCRGB_H_ */ 

[Azagaros]

first thing I will note is in the casting:

You use unsigned char which is one byte usually. and signed int which is 2 or 4 bytes depending on system. I was suspecting an offset in the pointer wrangling but wasn't sure where.

The other thing that might be causing your problem is the conversion of unsigned char to signed int. I would keep the signing consistent across things, in the single byte character to multi-byte ints might have the sign bit of the unsigned maintained. In other words 255 unsigned char might come out a -1 signed int.

I would set up a simple test to verify this conversion is coming out the way you expect it to.

[dingyong198608]

can you give me some details about the problem? but I have to change unsigned char into int type because image should be number to represent the pixel. How can I change it?
And I think that the problem is not the 2 or 4 byte conversion from char to int because some of pixels are still right.

Also, I find that the evaluation changed the value of (*gdatap)[0][0] into 12 when it execute the sentence (*gdatap)[192][0] = ImageData[192][0][1].

In addition, I find the latter evaluation begins to change the previous values after the row 165, from row 166

[dingyong198608]

Finally, I solved this problem. It is reading problem, instead of conversion