RTI Image File Format

The RTI Image File Format

C. Furlong
WPI-ME/CHSLT

Overview

RTI images are non-standard bitmap based format used in the 16/32-bit data images generated by WPI-ME/CHSLT's opto-electronic holography systems. RTI images are written in binary format and consisting of:

216 bytes header,
40 bytes of "dead" space, and
16/32-bit data written in raster format

Data stored in the 16-bit images is of the short int type (2 bytes) and data stored in the 32-bit images is of the float type (4-bytes). The header of an RTI image can be read by defining the following C structures:

struct TimeCode
{
short int scene;   /* 0-999       */
short int hour;    /* 0- 23       */
short int minute; /* 0- 59       */
short int second; /* 0- 59       */
short int frame;   /* 0- 29       */
short int field;   /* 1- 2 Note: -1 indicated non-valid field */
};

typedef struct _FileHeaderData {
char signiture[4];
char suffix[4];
char dataSize;
char camNum; /* Added for holograms */
short int space1;
short int saveMethod;
short int formatRevision;
short int xMin;
short int yMin;
short int xMax;
short int yMax;
long annotationOffset;
long dataOffset;
char comment[80];
double xScale;
double yScale;
double zScale;
double xOrig;
double yOrig;
double zOrig;
char pUnits[20];
char iUnits[20];
struct TimeCode timeCode;
short int fileType;
} FileHeaderData;

First example:

Reads RTI file (16/32-bit) and extracts values on area of interest (AOI) defined by image coordinates (x1, y1)-(x2,y2). Extracted data can be subsampled with delta increments: Delta_x and Delta_y.
Extracted data is written to output file in ASCII format.

/*                                                                                                       */
/* This program reads RTI 16 and 32 bit image files and         */
/* writes an output file with data number, pixel coordinates, */
/* and corresponding assigned values.                                     */
/*                                                                                                      */
/* Cosme Furlong                                                                          */
/* WPI-ME/Laser Laboratory                                                      */
/*                                                                                                      */

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <unistd.h>
#include "rtiheader.h"

#define HOLO_SIGN "RTI"
#define PI (3.141592654)

main(argc,argv)
int argc;
char **argv;
{
    char iname[80];
    char head_rti[10];
    int IXSIZE;
    int IYSIZE;
    int datatype;
    int i, Xpo, Ypo;
    int size,count;
    int x1,x2,y1,y2,Del;
    int Off,corrV,nData;
    int Del_x,Del_y;
    FILE *handle_i,*handle_o;
    FileHeaderData hh;
    short value;
    float fval32;
    float maxv;
    void *pdata;

if ( argc < 8 ) {
printf("Error %s syntax: inp.rti out.txt x1 y1 x2 y2 del\n",argv[0]);
exit(-1);
}

if ( (handle_i=fopen(argv[1],"r"))==NULL ) {
printf("Could not open INPUT file!\n");
exit(1);
}

fread(head_rti,10,1,handle_i);

if (strncmp(head_rti,HOLO_SIGN,strlen(HOLO_SIGN)) == 0) {
printf("Input file is an RTI file.\n\n");

} else {

printf("Input file is NOT an RTI file. Exiting....\n");
exit(1);
}

x1 = atoi(argv[3]);
y1 = atoi(argv[4]);
x2 = atoi(argv[5]);
y2 = atoi(argv[6]);
Del= atoi(argv[7]);
Del_x = (x2 - x1);
Del_y = (y2 - y1);

printf("Provided coordinates:\n");
printf("(%d,%d)-(%d,%d)-%d\n\n",x1,y1,x2,y2,Del);

if ( (x1 > x2) || (y1 > y2) ) {
printf("Please check input coordinates. Exiting.\n");
exit(1);
}

/* Set input file location to first bit */

fseek(handle_i,0,SEEK_SET);

/* Read 256-bit RTI header */

fread(&hh,sizeof(hh),1,handle_i);

/* Shift 256 bits */

fseek(handle_i,256,SEEK_SET);

/* Image size */

IXSIZE = (hh.xMax - hh.xMin + 1);
IYSIZE = (hh.yMax - hh.yMin + 1);
size = IXSIZE*IYSIZE;
printf("Image size is: %d x %d\n",IXSIZE,IYSIZE);

/* Extract data type */

datatype = hh.dataSize;
printf("RTI file is %d bits.\n",datatype);

if (datatype == 8) {
printf("This is not a data file. Exiting.\n");
exit(1);
}

/* OPEN OUTPUT FILE: ASCII FILE*/

if ( (handle_o=fopen(argv[2],"w")) == NULL)
    {
     printf("Could not open OUTPUT file!\n");
     exit(1);
}

/* SWITCH DEPENDING ON DATATYPE */

    switch(datatype)
      {
      case(16):

printf("\n");
printf("Working....\n\n");

        pdata = malloc(size*2);
        if (fread(pdata,size*2,1,handle_i) < 0) {
           printf("Reading input file error. Exiting.\n");
           exit(1);
        }

/* Find data offset and shift data pointer */

        Off = 512*y1+x1;
        printf("Input file offset: %d\n",Off);
        fseek(handle_i,Off,SEEK_SET);

         nData = 0;
        for (Ypo=0; Ypo <= Del_y; Ypo += Del) {
            for (Xpo=0; Xpo <= Del_x; Xpo += Del) {
               value = ((short*)pdata)[Off+Xpo];

/* Print to output file. Applying correction to Y coordinate. */

corrV = 0.8*(y1+Ypo);

               nData++;
              fprintf(handle_o,"%d %d %d %d\n",nData,x1+Xpo,corrV,value);
            }
            Off += (512)*Del;
         }

printf("Number of data points written: %d\n",nData);

printf("\n");
printf("Done!\n\n");

break;

case(32):

printf("\n");
printf("Working....\n\n");

         pdata = malloc(size*4);
         if (fread(pdata,size*4,1,handle_i) < 0) {
         printf("Reading input file error. Exiting.\n");
         exit(1);
         }

/* Find data offset and shift data pointer */

        Off = 512*y1+x1;
        printf("Input file offset: %d\n",Off);
        fseek(handle_i,Off,SEEK_SET);

        nData = 0;
        for (Ypo=0; Ypo <= Del_y; Ypo += Del) {
          for (Xpo=0; Xpo <= Del_x; Xpo += Del) {
             fval32 = ((float*)pdata)[Off+Xpo];
             if (fabs(fval32) > 1e20) fval32 = 0;

/* Write all pixels. Including bad ones.

if (fval32) {
*/

/* Print to output file. Applying correction to Y coordinate. */

corrV = 0.8*(y1+Ypo);

               nData ++;
              fprintf(handle_o,"%d %d %d %f\n",nData,x1+Xpo,corrV,fval32);
/*
            }
*/
          }
          Off += (512)*Del;
        }
        printf("Number of data points written: %d\n",nData);

printf("\n");
printf("Done!\n\n");

break;

default:

printf("Datatype not supported. Exiting...\n");
exit(1);

} /* End of switch */

/* CLOSE FILES AND FREE MEMORY */

    fclose(handle_i);
    fclose(handle_o);
    free(pdata);
}

Second example:

Reads RTI file (16/32-bit) and writes 8-bit SGI image.

/* Program: rti2sgi.c                   */
/*                                              */
/* This program reads RTI 16/32-bit image files and        */
/* writes out a valid Grayscaled SGI image file (8-bit).      */
/* WPI-ME/Laser Laboratory     */
/* Written in ANSI C by              */
/* C. Furlong                               */

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <unistd.h>

#define HOLO_SIGN "RTI"
#define PI (3.141592654)

putbyte(outf,val)
FILE *outf;
unsigned char val;
{
unsigned char buf[1];

buf[0] = val;
fwrite(buf,1,1,outf);
}

putshort(outf,val)
FILE *outf;
unsigned short val;
{
unsigned char buf[2];

    buf[0] = (val>>8);
    buf[1] = (val>>0);
    fwrite(buf,2,1,outf);
}

static int putlong(outf,val)
FILE *outf;
unsigned long val;
{
unsigned char buf[4];

    buf[0] = (val>>24);
    buf[1] = (val>>16);
    buf[2] = (val>>8);
    buf[3] = (val>>0);
    return fwrite(buf,4,1,outf);
}

typedef struct _FileHeaderData {
char     signiture[4];
char     suffix[4];
char     dataSize;
char     camNum;    /*         Added for holograms */
short int    space1;
short int    saveMethod;
short int    formatRevision;
short int    xMin;
short int    yMin;
short int    xMax;
short int    yMax;
long     annotationOffset;
long     dataOffset;
char     comment[80];
double    xScale;
double    yScale;
double    zScale;
double    xOrig;
double    yOrig;
double    zOrig;
char     pUnits[20];
char     iUnits[20];
struct    TimeCode timeCode;
short int    fileType;
} FileHeaderData;

main(argc,argv)
int argc;
char **argv;
{
    char    iname[80];
    char    head_rti[10];
    unsigned char outbuf[512];
    unsigned char bufc[2];
    int     IXSIZE;
    int     IYSIZE;
    int     datatype;
    int     i, Xpo, Ypo;
    int     size,count,count2;
    int     maxi,mini,Diffi;
    FILE    *handle_i,*handle_o;
    FileHeaderData hh;
    short    value;
    float    fval32;
    float    maxv,minv,Diff;
    void    *pdata;

if ( argc < 3 ) {
printf("\nError. Try: \n");
printf(">%s input_rti(16/32) output_sgi(8).\n", argv[0]);
}

if ( (handle_i=fopen(argv[1],"r"))==NULL ) {
printf("Could not open INPUT file!\n");
exit(1);
}

fread(head_rti,10,1,handle_i);

if (strncmp(head_rti,HOLO_SIGN,strlen(HOLO_SIGN)) == 0) {
printf("Input file is an RTI file.\n");

} else {

printf("Input file is NOT an RTI file. Exiting....\n");
exit(1);
}

fseek(handle_i,0,SEEK_SET);
fread(&hh,sizeof(hh),1,handle_i);
fseek(handle_i,256,SEEK_SET);

IXSIZE = (hh.xMax - hh.xMin + 1);
IYSIZE = (hh.yMax - hh.yMin + 1);

size = IXSIZE*IYSIZE;

printf("Image size is: %d x %d\n",IXSIZE,IYSIZE);

datatype = hh.dataSize;
printf("RTI file is %d bits.\n",datatype);

printf("Signature: %c\n",hh.signiture[0]);
printf("Space: %d\n",hh.space1);
printf("Save method: %d\n",hh.saveMethod);
printf("Format revision: %d\n",hh.formatRevision);
printf("xMin: %d\n",hh.xMin);
printf("yMin: %d\n",hh.yMin);
printf("xMax: %d\n",hh.xMax);
printf("yMax: %d\n",hh.yMax);
printf("Annotation offset: %d\n",hh.annotationOffset);
printf("Data offset: %d\n",hh.dataOffset);
printf("xScale: %lf\n",hh.xScale);
printf("yScale: %lf\n",hh.yScale);
printf("zScale: %lf\n",hh.zScale);
printf("xOrig : %lf\n",hh.xOrig);
printf("yOrig : %lf\n",hh.yOrig);
printf("zOrig : %lf\n",hh.zOrig);
printf("pUnits: %c\n",hh.pUnits[3]);
printf("iUnits: %c\n",hh.iUnits[3]);

/* OPEN OUTPUT FILE: SGI-IRIS */

if ( (handle_o=fopen(argv[2],"w")) == NULL) {
printf("Could not open OUTPUT file!\n");
exit(1);
}

    putshort(handle_o,474);       /* MAGIC                       */
    putbyte(handle_o,0);          /* STORAGE is VERBATIM         */
    putbyte(handle_o,1);          /* BPC is 1                    */
    putshort(handle_o,2);         /* DIMENSION is 2              */
    putshort(handle_o,IXSIZE);    /* XSIZE                       */
    putshort(handle_o,IYSIZE);    /* YSIZE                       */
    putshort(handle_o,1);         /* ZSIZE                       */
    putlong(handle_o,0);          /* PIXMIN is 0                 */
    putlong(handle_o,255);        /* PIXMAX is 255               */

    for(i=0; i<4; i++) {      /* DUMMY 4 bytes       */
        putbyte(handle_o,0);
    }

    strcpy(iname,"WPI-ME/CHSLT");
    fwrite(iname,80,1,handle_o); /* IMAGENAME           */
    putlong(handle_o,0);          /* COLORMAP is 0       */

    for(i=0; i<404; i++) {     /* DUMMY 404 bytes     */
        putbyte(handle_o,0);
    }

    switch(datatype)
      {
      case(16):

/* Use the extraction of high and lower byte technique.
It does not require memory allocation!.

maxi = 0;
for(Ypo=0; Ypo<IYSIZE; Ypo++) {
         for(Xpo=0; Xpo<IXSIZE; Xpo++) {
     fread(bufc,2,1,handle_i);
     value = (bufc[0]<<8)+(bufc[1]<<0);

if (abs(value) > abs(maxi)) maxi = value;

outbuf[Xpo] = value*8722/256;

printf("Value(%d,%d): %d\n",Xpo,Ypo,value);
}

fwrite(outbuf,IXSIZE,1,handle_o);
}
printf("Maximum pixel value: %d\n",maxi);

pdata = malloc(size*2);

        if (fread(pdata,size*2,1,handle_i) < 0) {
           printf("Reading input file error. Exiting.\n");
           exit(1);
        }

mini = maxi = 0;
for (Xpo=0; Xpo<size; Xpo++) {
     value = ((short*)pdata)[Xpo];
   if ( value >= maxi ) maxi = value;
   if ( value <= mini ) mini = value;
}
printf("Max.value(%d bit mode): %d\n",datatype,maxi);
printf("Min.value(%d bit mode): %d\n",datatype,mini);

Diffi = maxi-mini;
if (abs(Diffi) < 1) {
printf("RTI image contains no modulation. Exiting...\n");
exit(-1);
}

printf("Writing output file...\n\n");
count = count2 = 0;
for(Ypo=0; Ypo<IYSIZE; Ypo++) {
        for(Xpo=0; Xpo<IXSIZE; Xpo++) {
    value = ((short*)pdata)[count2+Xpo];
    outbuf[Xpo] = (value-mini)*256/Diffi;
   }
   fwrite(outbuf,IXSIZE,1,handle_o);
   count++;
   count2 = count*IXSIZE;
}

break;

case(32):

pdata = malloc(size*4);

if (fread(pdata,size*4,1,handle_i) < 0) {
printf("Reading input file error. Exiting.\n");
exit(-1);
}

minv = 0.0;
maxv = 0.0;
for (Xpo=0; Xpo<size; Xpo++) {
   fval32 = ((float*)pdata)[Xpo];
   if (fabs(fval32) >= 1.0e20) fval32 = 0.0;
   if ( fval32 >= maxv ) maxv = fval32;
   if ( fval32 <= minv ) minv = fval32;
}
        printf("Max.value(%d bit mode): %f*pi\n",datatype,maxv/PI);
        printf("Min.value(%d bit mode): %f*pi\n",datatype,minv/PI);

Diff = maxv-minv;
if (fabs(Diff) < 1e-10) {
printf("RTI image contains no modulation. Exiting...\n");
exit(-1);
}

printf("Writing output file...\n\n");
count = count2 = 0;
for(Ypo=0; Ypo<IYSIZE; Ypo++) {
   for(Xpo=0; Xpo<IXSIZE; Xpo++) {
    fval32 = ((float*)pdata)[count2+Xpo];
    if (fabs(fval32) >= 1.0e20) {
     outbuf[Xpo] = 0.0;
    } else {
     outbuf[Xpo] = (fval32-minv)*256/Diff;
    }
   }
   fwrite(outbuf,IXSIZE,1,handle_o);
   count++;
   count2 = count*IXSIZE;
}

break;

default:

printf("Not a data file - PBM file. Exiting...\n");
exit(-1);

} /* switch */

printf("\n Done!\n");

/* CLOSE FILES AND FREE MEMORY */

    fclose(handle_i);
    fclose(handle_o);
    free(pdata);
}

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