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Hi Thanh,
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<div class="">On Jul 17, 2016, at 7:41 PM, The Thanh Han <<a href="mailto:hanthethanh@gmail.com" class="">hanthethanh@gmail.com</a>> wrote:</div>
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<div class="gmail_default" style="font-size:small">the real question one should ask is why StemV is required, since it's already included in the font itself.</div>
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<div>I think I can explain that.</div>
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<div>For a Type 1 font, StemV is the Hinting parameter StdVW .</div>
<div>pdfTeX already knows this: </div>
<div> ptexlib.h:363: , {"StemV", "StdVW”}</div>
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<div><a href="http://partners.adobe.com/public/developer/en/font/T1_SPEC.PDF" class="">http://partners.adobe.com/public/developer/en/font/T1_SPEC.PDF</a></div>
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<div>PDF uses the Font Descriptor dictionary in several ways.</div>
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<div> #1. Firstly, if the font program itself is *not* present, then it can substitute </div>
<div> something that looks similar, having similar widths in vertical strokes.</div>
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<div> #2. When the font *is* available, there are still issues; especially at</div>
<div> low resolution. Then the “hinting” is used in choosing which pixels to</div>
<div> include when following the outline description.</div>
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<div> #3. Even at high resolution, there is a possible use, related to #1.</div>
<div> The time required to produce the full hi-res image of a portion of</div>
<div> a page may be quite large (a few seconds, say).</div>
<div> Instead of presenting a blank page until it’s ready, a quick mock-up</div>
<div> is first shown, perhaps using a substitute font with cached letter forms.</div>
<div> This is later replaced with the full image, when ready.</div>
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<div>I cannot find any documentation to justify that #3 is used in any specific renderer, </div>
<div>but I've certainly seen rough images appear prior to the full hi-res. version.</div>
<div>Note that the /Flags parameter conveys information about characteristics</div>
<div>of the script that the font implements, so is used in the selection of substitute fonts.</div>
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<div>Here’s an extract from the PDF Spec. which certainly refers to usage #1; </div>
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9.8 Font Descriptors<br class="">
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9.8.1General<br class="">
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A font descriptor specifies metrics and other attributes of a simple font or a CIDFont as a whole, as distinct from the metrics of individual glyphs. These font metrics provide information that enables a conforming reader to synthesize a substitute font or
select a similar font when the font program is unavailable. The font descriptor may also be used to embed the font program in the PDF file. </div>
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<div class="gmail_default" style="font-size:small">Thanh</div>
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<div class="">Hope this helps.</div>
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<div class=""><span class="Apple-tab-span" style="white-space:pre"></span>Ross</div>
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Dr Ross Moore</span></b></span></div>
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