[cairo] cairo Summer-of-code participant introduction

Kai-Uwe Behrmann ku.b at gmx.de
Thu Apr 24 21:59:39 PDT 2008

A C library implementing the 16-bit HALF float with a liberal license 
(BSD) would be very welcome. It could be shared or used in Oyranos as 

Cairo may consider to not to rely on some particular tone mapping library 
without a framework for flexible and language independent pluging in of 
new operators. The Oyranos CMS is designed toward providing the later.

kind regards
Kai-Uwe Behrmann
developing for colour management 
www.behrmann.name + www.oyranos.org

Am 23.04.08, 11:02 +0800 schrieb xie guofu:

> instead of gamma compressed 8-bit integers. It allows values outside of the
> [0..1] range, creating a much larger effective gamut. It also has greater
> precision because the half-precision format has a 10-bit significand.
> In my solution, the 16-bit floating-point data type is implemented as a C
> struct, half, which is designed to behave as much as possible like the
> standard floating-point data types built into the C language. half numbers
> have 1 sign bit, 5 exponent bits, and 10 mantissa bits. The interpretation
> of the sign, exponent and mantissa is analogous to IEEE-754 floating-point
> numbers. half supports normalized and denormalized numbers, infinities and
> NANs (Not A Number). The range of representable numbers is roughly 6.0×10-8
> - 6.5×104; numbers smaller than 6.1×10-5 are denormalized. Conversions from
> float to half round the mantissa to 10 bits; the 13 least significant bits
> are lost. Conversions from half to float are lossless; all half numbers are
> exactly representable as float values.

> One problem with HDR has always been in viewing the images. Mundane CRTs,
> LCDs, prints, and other methods of displaying images only have a limited
> dynamic range. Thus various methods of converting HDR images into a viewable
> format have been developed, generally called "tone mapping". In the project,
> I will research on how the human eye and visual cortex perceive a scene,
> trying to show the whole dynamic range while retaining realistic color and
> contrast. In the project, I will present an adaptive logarithmic mapping
> approach, which was introduced in Drago et al. [2]. Of course, if there is
> enough time, I will implement other tone mapping algorithms, for example,
> Fattal et al. [3] and Mantiuk et al. [4].
> [2] Adaptive Logarithmic Mapping For Displaying High Contrast Scenes
> http://www.mpi-inf.mpg.de/resources/tmo/logmap/
> [3] Gradient domain high dynamic range compression
> http://www.cs.huji.ac.il/~danix/hdr/
> [4] A Perceptual Framework for Contrast Processing of High Dynamic Range
> Images
> http://www.mpi-inf.mpg.de/~mantiuk/contrast_domain/

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