Writing a Targa file not working from an array Post: 303016286

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Top Forums Programming Writing a Targa file not working from an array Post 303016286 by Don Cragun on Tuesday 24th of April 2018 12:27:25 AM

04-24-2018

Registered User

One might note that the 1st code fragment (making the wild assumption that none of the obscured lines make any updates to the ctr variable), sets and writes three successive elements of the array a[] each time through the loop. This seems to be what you want to do, although it would probably be much more efficient to just have the loop set elements of the array and then use a single write of the entire array when the loop finishes.

The second code fragment sets elements of the array in about the same way in the first loop. But, the second loop writes elements 0, 1, and 2 of the array on the 1st pass; elements 1, 2, and 3 on the 2nd pass; 2, 3, and 4 on the 3rd pass; etc. To be logically equivalent to the first code fragment, you would need to change:

Code:

for (int i=0; i<image.getHeight()*image.getWidth(); i++) {

to something more like:

Code:

for (int i=0; i<image.getHeight()*image.getWidth(); i+=3) {

But, again, writing the entire array with a single write would seem to be much more efficient than writing the entire array one byte at a time.

One would expect that the file produced by the first code fragment you showed us is much smaller than the file produced by the second code fragment you showed us (by about a factor of 3). Maybe that would be a hint as to what might not be working???

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LEARN ABOUT DEBIAN

ra_t8

RA_T8(1)						      General Commands Manual							  RA_T8(1)

NAME

       ra_t8 - convert RADIANCE picture to/from Targa 8-bit image file

SYNOPSIS

       ra_t8 [ -d ][ -b ][ -c ncolors ][ -g gamma ][ -e +/-stops ][ -n sampfac ] input [ output ]
       ra_t8 -r [ -g gamma ][ -e +/-stops ] [ input [ output ] ]

DESCRIPTION

       Ra_t8  converts	between RADIANCE and Targa 8-bit color-mapped image files (type 1 in Targa's documentation).  In the default mode, a RADI-
       ANCE picture is converted to a color-mapped Targa file of the same horizontal and vertical dimensions with 8-bits per pixel.  The -d option
       turns  off  dithering.  The -b option converts the image to black and white.  Only with this option can the input be taken from stdin.  The
       -c option allows fewer than 256 colors.	The -g option specifies the exponent used in gamma correction; the default value is 2.2.  An expo-
       nent  of  1.0 turns gamma correction off.  The -e option specifies an exposure compensation in f-stops (powers of two).	Only integer stops
       are allowed, for efficiency.  The -n option specifies a sampling factor for neural  network  color  quantization.   This  value	should	be
       between	1  and	80,  where  1 takes the longest and produces the best results in small areas of the image.  If no value is given, a faster
       median cut algorithm is used.  The -r option invokes a reverse conversion, from an 8-bit Targa file to a RADIANCE picture.  If  the  output
       file is missing, the standard output is used.

AUTHORS

       Greg Ward
       Anthony Dekker provided the code for neural network color quantization

BUGS

       Run-length encoded files can be read but not written with this program.

SEE ALSO

       pfilt(1), ra_bmp(1), ra_bn(1), ra_ppm(1), ra_pr(1), ra_pr24(1), ra_t16(1), ra_tiff(1), ximage(1)

RADIANCE
							      5/30/95								  RA_T8(1)

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