Replace image with PNG image in cHRM section

See #405

index.html

@@ -3272,7 +3272,7 @@ <h2><span class="chunk">cHRM</span> Primary chromaticities and white point</h2>
 <!-- 99 72 82 77 -->63 48 52 4D
 </pre>
           <p>The <span class="chunk">cHRM</span> chunk may be used to specify the 1931 CIE <i>x,y</i> chromaticities of the red,
-          green, and blue display primaries used in the image, and the referenced <a>white point</a>. See <a href=
+          green, and blue display primaries used in the <a>PNG image</a>, and the referenced <a>white point</a>. See <a href=
           "#C-GammaAppendix"></a> for more information. The <a class="chunk" href="#11iCCP">iCCP</a>, and <a class="chunk" href=
           "#11sRGB">sRGB</a> chunks provide more sophisticated support for color management and control.</p>