user2070: This is the actual source image to a video track in Premiere (a PNG):

With no resizing whatsoever, and .flv output, this is a resultant frame from the exported video:

How could I improve the output quality, especially the text?
What settings should I use

I've tried to max out pretty much everything in the FLV export settings.
And now I moved to MP4 output with H.264 encoding, but still get poor quality stills.
Here are the MP4 Export settings, what should I change?


Solution
Inspired from the answers, turns out that have to set the source to Progressive when creating a New Sequence (instead of Fields: Upper)

this is why I did not get better results whatever my configuration once I had created a sequence with Fields set to Upper
and this is why the following settings for my next project, yielded good stills

although also using higher resolution, so not sure high that plays into the test results
H.264 / MP4 Export settings otherwise the same





user16640: I had the same issue with image quality for a 4K video I was trying to produce. I found that for my situation the image was always very blurry upon an export, so I had to change the Format and Preset. A very nice 4K format that enabled my images to turn out crispy is the H.264 which is quite widely used, and already has a built in default YouTube 2160p 4K preset which works well. Once you select this you can compare how the output will look against the source formatting by switching between Source and Output. Eventually, you can tune the default preset and make your own in order to get a nice 4K video out of the application.


user3908: That looks more like a 'field' from the video, rather than a frame -- jagged diagonals are the tell.
If your video is interlaced, you may only get half the vertical resolution in a still, unless you specifically set it to output a full frame. Check the export settings.

2070: <p>This is the actual <strong>source image</strong> to a video track in Premiere (a PNG):
<img src="https://i.stack.imgur.com/NiZYL.jpg" alt="decentqualityinput" /></p>
<p>With no resizing whatsoever, and .flv output, this is a <strong>resultant frame</strong> from the exported video:
<img src="https://i.stack.imgur.com/wg7j4.png" alt="poorqualityoutput" /></p>
<h3>How could I improve the output quality, especially the text?</h3>
<p>What settings should I use</p>
<ul>
<li>I've tried to max out pretty much everything in the FLV export settings.</li>
<li>And now I moved to MP4 output with H.264 encoding, but still get poor quality stills.</li>
<li>Here are the MP4 Export settings, what should I change?</li>
</ul>
<p><img src="https://i.stack.imgur.com/Bcutp.png" alt="MP4-poor" /></p>
<h3>Solution</h3>
<p>Inspired from the answers, turns out that have to set the source to Progressive when creating a New Sequence (instead of Fields: Upper)</p>
<ul>
<li>this is why I did not get better results whatever my configuration once I had created a sequence with Fields set to Upper</li>
<li>and this is why the following settings for my next project, yielded good stills
<ul>
<li>although also using higher resolution, so not sure high that plays into the test results</li>
<li>H.264 / MP4 Export settings otherwise the same</li>
</ul>
</li>
</ul>
<p><img src="https://i.stack.imgur.com/H0USB.png" alt="ProgressiveFields" /></p>
 16640: <p>I had the same issue with image quality for a 4K video I was trying to produce. I found that for my situation the image was always very blurry upon an export, so I had to change the Format and Preset. A very nice 4K format that enabled my images to turn out crispy is the <em>H.264</em> which is quite widely used, and already has a built in default <em>YouTube 2160p 4K</em> preset which works well. Once you select this you can compare how the output will look against the source formatting by switching between <em>Source</em> and <em>Output</em>. Eventually, you can tune the default preset and make your own in order to get a nice 4K video out of the application.</p>

<p><a href="https://i.stack.imgur.com/i4Knk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/i4Knk.png" alt="enter image description here"></a></p>
 3908: <p>That looks more like a 'field' from the video, rather than a frame -- jagged diagonals are the tell.</p>

<p>If your video is interlaced, you may only get half the vertical resolution in a still, unless you specifically set it to output a full frame. Check the export settings.</p>
