Version 0.1.0

htrdr-image(5)

NAME

htrdr-image - format of the images generated by htrdr(1)

DESCRIPTION

The htrdr-image is a raw image file format where data are stored in plain text. Characters after the # character are considered as comments and are thus ignored as well as empty lines. The first valid line stores 2 unsigned integers that represent the image definition, i.e. the number of pixels per line and per column. Then each line stores 4 pairs of floating points data representing the pixel color encoded in the CIE 1931 XYZ color space and the time spent per realisation to estimate the pixel. The first, second and third pair encodes the estimated radiance in W.sr-1.m-2 of the X, Y and Z pixel components, respectively. The first value of each pair is the expected value of the estimated radiance while the second one is its associated standard deviation. The fourth pair saves the estimate in microseconds of the per radiative path computation time and its standard error.

Pixels are sorted line by line, with the origin defined at the top left corner of the image. With an image definition of N by M pixels, with N the number of pixels per line and M the overall number of lines in the image, the first N pixels correspond to the pixels of the top line of the image, the following N pixels are the pixels of the second line and so on.

Note that the htpp(1) program can be used to convert an htrdr-image in a regular PPM image [1].

GRAMMAR

<htrdr-image>    ::= <definition>
                     <pixel>
                   [ <pixel> ... ]

<definition>     ::= <width> <height>
<width>          ::= INTEGER
<height>         ::= INTEGER

<pixel>          ::= <X> <Y> <Z> <time>
<X>              ::= <estimate>
<Y>              ::= <estimate>
<Z>              ::= <estimate>
<time>           ::= <estimate>

<estimate>       ::= <expected-value> <standard-error>
<expected-value> ::= REAL
<standard-error> ::= REAL

EXAMPLE

The following output is emitted by htrdr(1) invoked to render an image of 800 by 600 pixels. Note that actually the comments or the blank lines are not necessarily written as it by htrdr(1); they are used here only to help in understanding the data layout. The comment after each pixel gives the two dimensional index of the pixel in the image: the first and second integer is the index of the line and the column of the pixel in the image, respectively.

800 600 # Image definition

# Pixels of the 1st line
2.55e-4 2.90e-5 3.75e-4 4.48e-5 3.20e-4 3.16e-5 306.484 259.723 # (1,1)
2.95e-4 3.37e-5 3.39e-4 4.16e-5 3.38e-4 4.60e-5 18.3633 2.66317 # (2,1)
3.76e-4 5.43e-5 3.13e-4 3.48e-5 3.38e-4 3.32e-5 19.6252 2.67015 # (3,1)
              ...
7.13e-4 1.14e-4 7.66e-4 1.35e-4 7.97e-4 1.26e-4 119.820 93.7820 # (799,1)
6.59e-4 1.14e-4 7.47e-4 1.41e-4 4.39e-4 7.33e-5 24.8655 2.46348 # (800,1)

# Pixels of the 2nd line
3.33e-4 6.02e-5 4.21e-4 7.66e-5 3.44e-4 3.81e-5 19.4580 2.50692 # (1,2)
3.50e-4 4.93e-5 3.23e-4 2.52e-5 3.03e-4 2.42e-5 102.566 81.2936 # (2,2)
2.72e-4 4.69e-5 3.41e-4 4.12e-5 2.52e-4 2.06e-5 25.5801 5.37736 # (3,2)
              ...
7.52e-4 1.31e-4 8.91e-4 1.84e-4 5.48e-4 1.30e-4 46.5418 12.4728 # (799,2)
6.82e-4 1.42e-4 6.61e-4 7.85e-5 4.44e-4 5.99e-5 59.8728 32.1468 # (800,2)

              ...

# Pixels of the 600th line
2.69e-4 7.44e-5 2.31e-4 2.56e-5 1.95e-4 2.30e-5 43.8242 15.0047 # (1,600)
4.32e-4 1.25e-4 2.22e-4 2.22e-5 2.04e-4 2.60e-5 25.5498 1.73942 # (2,600)
2.78e-4 5.81e-5 2.75e-4 4.99e-5 2.17e-4 3.30e-5 38.4448 7.16199 # (3,600)
            ...
3.54e-4 4.32e-5 3.07e-4 3.80e-5 2.38e-4 2.49e-5 102.893 36.9865 # (799,600)
3.07e-4 2.61e-5 4.60e-4 1.13e-4 2.69e-4 4.29e-5 42.75070 11.913 # (800,600)

NOTES

1. Portable PixMap - http://netpbm.sourceforge.net/doc/ppm.html

SEE ALSO

htpp(1), htrdr(1)