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17/03 — 2020
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<span class="stats-number">
32.36
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3.2
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<h1>
Font Size Fallacies
</h1>
<div class="post-text">
<p>I am not an expert with fonts, but I do have some
experience <sup id="fnref1"><a href="#fn1" rel="footnote">1</a></sup>, and common sense. This post aims to debunk some
misconceptions about font sizes!</p>
<p>11 px on your display is <em>probably not</em> 11 px on my display.
Let's do some quick math. I have two displays, 1366x768 @
21” and another with 1920x1080 @ 13”, call them <code>A</code> and
<code>B</code> for now.</p>
<p>Display <code>A</code> has 1,049,088 pixels. A pixel is a square, of
side say, <code>s</code> cm. The total area covered by my 21” display
is about 1,066 cm<sup>2</sup> (41x26). Thus,</p>
<pre><code>Display A
Dimensions: 1366x768 @ 21" (41x26 sq. cm)
1,049,088 s^2 = 1066
s = 0.0318 cm (side of a pixel on Display A)
</code></pre>
<p>Bear with me, as I repeat the number crunching for Display
<code>B</code>:</p>
<pre><code>Display B
Dimensions: 1920x1080 @ 13" (29.5x16.5 sq. cm)
2,073,600 s^2 = 486.75
s = 0.0153 cm (side of a pixel on Display B)
</code></pre>
<p>The width of a pixel on Display <code>A</code> is <em>double</em> the width of a
pixel on Display <code>B</code>. The area occupied by a pixel on Display
<code>A</code> is <em>4 times</em> the area occupied by a pixel on Display <code>B</code>.</p>
<p><em>The size of a pixel varies from display to display!</em></p>
<p>A 5x11 bitmap font on Display <code>A</code> would be around 4 mm tall
whereas the same bitmap font on Display <code>B</code> would be around
1.9 mm tall. A 11 px tall character on <code>B</code> is visually
equivalent to a 5 px character on <code>A</code>. When you view a
screenshot of Display <code>A</code> on Display <code>B</code>, the contents are
shrunk down by a factor of 2!</p>
<p>So screen resolution is not enough, how else do we measure
size? Pixel Density! Keen readers will realize that the 5<sup>th</sup>
grade math problem we solved up there showcases pixel
density, or, pixels per cm (PPCM). Usually we deal with
pixels per inch (PPI).</p>
<p><strong>Note:</strong> PPI is not to be confused with DPI <sup id="fnref2"><a href="#fn2" rel="footnote">2</a></sup> (dots
per inch). DPI is defined for printers.</p>
<p>In our example, <code>A</code> is a 75 ppi display and <code>B</code> is around
165 ppi <sup id="fnref3"><a href="#fn3" rel="footnote">3</a></sup>. A low ppi display appears to be
‘pixelated’, because the pixels are more prominent, much
like Display <code>A</code>. A higher ppi usually means you can view
larger images and render crispier fonts. The average desktop
display can stuff 100-200 pixels per inch. Smart phones
usually fall into the 400-600 ppi (XXXHDPI) category. The
human eye fails to differentiate detail past 300 ppi.</p>
<p><em>So … streaming an 8K video on a 60” TV provides the same
clarity as a HD video on a smart phone?</em></p>
<p>Absolutely. Well, clarity is subjective, but the amount of
detail you can discern on mobile displays has always been
limited. Salty consumers of the Xperia 1 <sup id="fnref4"><a href="#fn4" rel="footnote">4</a></sup> will say
otherwise.</p>
<p>Maybe I will talk about font rendering in another post, but
thats all for now. Don't judge a font size by its
screenshot.</p>
<div class="footnotes">
<hr/>
<ol>
<li id="fn1">
<p><a href="https://github.com/nerdypepper/scientifica">https://github.com/nerdypepper/scientifica</a> <a href="#fnref1" rev="footnote">↩</a></p>
</li>
<li id="fn2">
<p><a href="https://en.wikipedia.org/wiki/Dots_per_inch">https://en.wikipedia.org/wiki/Dots_per_inch</a> <a href="#fnref2" rev="footnote">↩</a></p>
</li>
<li id="fn3">
<p><a href="https://www.sven.de/dpi/">https://www.sven.de/dpi/</a> <a href="#fnref3" rev="footnote">↩</a></p>
</li>
<li id="fn4">
<p><a href="https://en.wikipedia.org/wiki/Sony_Xperia_1">https://en.wikipedia.org/wiki/Sony_Xperia_1</a> <a href="#fnref4" rev="footnote">↩</a></p>
</li>
</ol>
</div>
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<div class=intro>
Hi. <a href=https://peppe.rs/index.xml class=feed-button>Subscribe</a>
<p>I'm Akshay, I go by nerd or nerdypepper on the internet.</p>
<p>
I am a compsci undergrad, Rust programmer and an enthusiastic Vimmer.
I write open-source stuff to pass time. I also design fonts: scientifica, curie.
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<p>Send me a mail at [email protected] or a message at [email protected].</p>
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