3.5 Using hdri2tif
on High Dynamic Range Images
hdri2tif
emplois a range compression algorithm(6) to convert high dynamic range images into displayable, low dynamic range, TIFFs.
All the important HDRI formats are recognized in input:
- Floating point TIFFs as well as LogLuv encoded TIFFs;
- Radiance files, uncompressed or RLE packed;
- ILM's OpenEXR files.
Note that all formats must have 3 or 4 channels. The fourth channel will be considered as alpha information and will stay untouched in the output image.
hdri2tif
accepts the following options:
- `-middle-gray n'
-
- `-key n'
- Sets the value of the middle-gray in the image, default is 0.18. Range is [0..1]. Specifying a value of 0 will enable an histogram based automatic estimation (one can use `-verbose' to display the computed key value);
- `-simple'
- By default,
hdri2tif
uses a "dodging-and-burning" algorithm which is relatively costly(7). Specifying this option will force the use of a simpler algorithm that is well suited for images with a medium dynamic range (lower than 10 "zones"). Note that this method may produce bad results on very high dynamic range images;
- `-white n'
- Sets the luminance value in the image that will be mapped to pure white (1.0 in the low dynamic range output image). Setting this parameter to smaller values will produce more "burning". The default action is to set the white point to the maximum luminance in the image, which removes burning. This option is only meaningful when paired with the `-simple' option because the default algorithm automatically computes the white point. Specifying a value of 0 will enable an histogram based automatic estimation (one can use `-verbose' to display the computed value);
- `-gamma n'
- Specifies a gamma correction to be applied on the produced image. Gamma correction is performed after the range compression algorithm.
- `-nthreads n'
hdri2tif
can run in a multi-threaded mode for increased performance. This options specifies how many threads to use. This option has no effect when `-simple-operator' is used.
- `-verbose'
- Displays information while processing the image;
- `-help'
- Displays a brief help text.
The following options can be used to further control the "dodging-and-burning" algorithm. Modifying these options is not recommanded.
- `-numscales n'
- Specifies the number of gaussian convolutions to use when computing luminance information for each pixel. More gaussians mean a more precise result but also a slower computation. This option is only meaningfull with the "dodging-and-burning" algorithm (no `-simple'). Default is 8;
- `-sharpness n'
- Sets the sharpness parameter. Higher values mean sharper images. Default is 8;
- `-lzw'
- `-deflate'
- `-packbits'
- `-none'
- Selects compression method to use for output TIFF. `-lzw' is enabled by default.
This document was generated
by Aghiles Kheffache on July, 31 2003
using texi2html
3Delight 1.0.0. Copyright 2000-2003 The 3Delight Team.
All Rights Reserved.