Changeset 1925 for www


Ignore:
Timestamp:
Nov 8, 2007, 3:34:19 AM (13 years ago)
Author:
Sam Hocevar
Message:
  • Add information about gamma.
  • Add gradients beside all dithered images.
File:
1 edited

Legend:

Unmodified
Added
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  • www/study/index.html

    r1921 r1925  
    4141       class="inline" alt="Lenna (256x256BW)" />
    4242</p>
     43
     44<h3> Foreword </h3>
    4345
    4446<p> This document makes a lot of assumptions, such as the fact that input
     
    8486  <img src="out001.png" width="256" height="256"
    8587       class="inline" alt="50% threshold" />
     88  <img src="grad001.png" width="32" height="256"
     89       class="inline" alt="50% threshold gradient" />
    8690</p>
    8791
     
    9498  <img src="out002.png" width="256" height="256"
    9599       class="inline" alt="40% threshold" />
     100  <img src="grad002.png" width="32" height="256"
     101       class="inline" alt="40% threshold gradient" />
    96102  <img src="out003.png" width="256" height="256"
    97103       class="inline" alt="60% threshold" />
     104  <img src="grad003.png" width="32" height="256"
     105       class="inline" alt="60% threshold gradient" />
    98106</p>
    99107
     
    107115<p style="text-align: center;">
    108116  <img src="out004.png" width="256" height="256"
    109        class="inline" alt="2-bit threshold" />
     117       class="inline" alt="3-colour threshold" />
     118  <img src="grad004.png" width="32" height="256"
     119       class="inline" alt="3-colour threshold gradient" />
    110120  <img src="out005.png" width="256" height="256"
    111        class="inline" alt="3-bit threshold" />
     121       class="inline" alt="4-colour threshold" />
     122  <img src="grad005.png" width="32" height="256"
     123       class="inline" alt="4-colour threshold gradient" />
    112124</p>
    113125
     
    140152  <img src="out006.png" width="256" height="256"
    141153       class="inline" alt="25%, 50% and 75% halftoning" />
    142 </p>
    143 
    144 <p> Not bad for a start. But there is a lot to improve. </p>
     154  <img src="grad006.png" width="32" height="256"
     155       class="inline" alt="25%, 50% and 75% halftoning gradient" />
     156</p>
     157
     158<p> Not bad for a start. But there is a lot to improve. By the way, this
     159technique is covered by Apple’s
     160<a href="http://www.freepatentsonline.com/5761347.html">U.S. patent
     1615761347</a>. </p>
    145162
    146163<h3> 2.2. Screen artifacts </h3>
     
    155172</p>
    156173
    157 <h3> 2.3. Gamma considerations </h3>
     174<!--<p> Even if the shades -->
     175
     176<h3> 2.3. Introducing gamma </h3>
    158177
    159178<p> More importantly, if you are reading this document on a computer
     
    165184  <img src="pat004.png" width="240" height="80"
    166185       class="inline" alt="introducing gamma" />
     186</p>
     187
     188<p> The mapping linking grayscale steps to intensities is called <b>gamma
     189correction</b>. An approximate law for gamma correction is given as
     190<i>I = v<small><sup>γ</sup></small></i> where <i>v</i> is the coded colour
     191value (between 0 and 1), <i>I</i> is the perceived colour intensity (between
     1920 and 1) and <i>γ</i> is the gamma. Most modern computer systems use the
     193sRGB gamma model where <i>γ</i> equals 2.2. As can be seen, it is highly
     194non-linear: </p>
     195
     196<p style="text-align: center;">
     197  <img src="fig001.png" width="256" height="230" alt="introducing gamma" />
    167198</p>
    168199
     
    193224<p style="text-align: center;">
    194225  <img src="out007.png" width="256" height="256"
     226       class="inline" alt="gamma-aware 3-pattern halftoning" />
     227  <img src="grad007.png" width="32" height="256"
     228       class="inline" alt="gamma-aware 3-pattern halftoning gradient" />
     229  <img src="out008.png" width="32" height="256"
    195230       class="inline" alt="gamma-aware 6.25%, 25% and 50% halftoning" />
    196231</p>
    197232
    198233<!--
     234  <img src="out008.png" width="256" height="256"
     235       class="inline" alt="gamma-aware 6.25%, 25% and 50% halftoning" />
     236
    199237<p> Here is the application to Lenna, using the 0-0.2, 0.2-0.4, 0.4-0.6,
    2002380.6-0.8 and 0.8-1 ranges for black, white and the three patterns: </p>
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