<story><title>Image Dithering: Eleven Algorithms and Source Code</title><url>http://www.tannerhelland.com/4660/dithering-eleven-algorithms-source-code/</url></story><parent_chain></parent_chain><comment><author>mark-r</author><text>The article doesn&amp;#x27;t put enough emphasis on the need for gamma correction. If you dither a pure gray area of level 128, it will become approximately 50% white and 50% black. But when you display that back on the screen, because of gamma effects it will look closer to a level of 186!&lt;p&gt;A few years ago there was a need for 15-bpp or 16-bpp color images on phones rather than the 24-bpp images we usually work with, and dithering was a great way of producing them. No idea how much need there is today though.</text></comment>
<story><title>Image Dithering: Eleven Algorithms and Source Code</title><url>http://www.tannerhelland.com/4660/dithering-eleven-algorithms-source-code/</url></story><parent_chain></parent_chain><comment><author>dreamcompiler</author><text>Dithering trades sample resolution for sample frequency to convey the same information. For images, the underlying sample frequency usually doesn&amp;#x27;t change but the &lt;i&gt;apparent&lt;/i&gt; spatial sample frequency becomes lower in order to achieve more than one effective bit per (coarser) sample.&lt;p&gt;For one-dimensional signals like audio, the underlying sample frequency is usually increased while decreasing the sample resolution (often to 1 bit per sample). This keeps the effective Nyquist frequency where it needs to be while pushing noise much higher in frequency where it&amp;#x27;s very easy to remove with an analog filter. Delta-sigma modulation is perhaps the most common method of audio dithering (although the delta-sigma literature rarely uses the D word).&lt;p&gt;The reason images and audio usually use dithering in opposite ways is that images are usually post-processed for lower true sample resolution (and higher effective sample resolution) &lt;i&gt;after&lt;/i&gt; sampling, while audio is often sampled &lt;i&gt;initially&lt;/i&gt; at much higher than the Nyquist frequency because dithering is a planned part of the audio processing chain. But not always! Those are merely common use cases.</text></comment>