The thumbnail size is defined here:
https://cs.chromium.org/chromium/src/chrome/browser/thumbnails/thumbnail_service_impl.cc?rcl=8f3cf8617dc8c27d6b0155dd775d4beebd58d62c&l=24

Should be trivial to update; just need to double-check that the thumbnails aren't used for anything else which might depend on the current size.

Note that the comparison in comment 1 isn't entirely fair, because the "proposed" one is cropped differently. We'd just change the physical size, but otherwise keep the content the same.

Thanks for looking into it. Yup, I just scaled the image to be exactly half of its physical size to illustrate that the result will be sharper. The visible image content will be the same.

Currently, we take screenshots at 212x142. The display size on the NTP (after the changes for bug 734038) is 154x96.

I've attached before/after screenshots for changing the thumbnail size to match the NTP. The new thumbnails are sharper as expected. Additionally, there is a side effect that the cropping also changes slightly, probably due to the different aspect ratio. IMO the new cropping looks better - before, the left and right side were cut off, which can look weird depending on the content.

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Also, random fun fact: The current width of 212 dp has been in place since 2009 (https://codereview.chromium.org/194028), so it has survived at least two NTP redesigns/rewrites. The height has been updated once in 2014 (https://codereview.chromium.org/564973003), to closer match the aspect ratio of the NTP. I don't know why the size wasn't just matched to the NTP at that point.

Addition to comment 5: The cropping also depends on the window's aspect ratio at the time the screenshot is taken, so these exact results won't always reproduce. However, taking the screenshot at the correct aspect ratio will allow us to make informed decisions about the cropping (as a possible later followup). Right now with the aspect ratio mismatch, the cropping is just arbitrary.

Cool, this definitely looks better to me. In addition, the images would be a lot smaller, so we would save some space on people's hard drives.

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I looked for other parts of Chrome (besides the NTP) that use thumbnails. I could only find a single one, around ChromeExtensionsClient::GetPermittedChromeSchemeHosts: Experimental extensions can access them, and there is a single (non-experimental) extension that's whitelisted to use it as a "temporary hack" that's been in place since 2013. That extension also hasn't been updated since 2013, and in any case, we're not making any guarantees on the resolution of thumbnails.

So, in summary: Changing the size should be fine.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7c65a26c058cf485c61809dfa70f8cc9d92d5560

commit 7c65a26c058cf485c61809dfa70f8cc9d92d5560
Author: Marc Treib <treib@chromium.org>
Date: Thu Jun 22 08:42:18 2017

Adjust thumbnail size to match the display size on the NTP

This makes the NTP thumbnails look less blurry (before/after
screenshots can be found on the bug). As a bonus, we'll take smaller
screenshots, saving CPU/GPU cycles and disk space.

As a fun fact, the current width of 212 dp has been in place since 2009
(https://codereview.chromium.org/194028), so it has survived at least
two NTP redesigns/rewrites. The height has been updated once in 2014
(https://codereview.chromium.org/564973003), to closer match the aspect
ratio of the NTP. I don't know why the size wasn't fully matched to the
NTP at that point.

Bug:  734981 
Change-Id: Ifecfa28e4ca97d17f819b6aefb63fba915235d95
Reviewed-on: https://chromium-review.googlesource.com/543143
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481481}
[modify] https://crrev.com/7c65a26c058cf485c61809dfa70f8cc9d92d5560/chrome/browser/thumbnails/thumbnail_service_impl.cc

Note that the fix will only apply for newly-taken thumbnails. Any existing ones will keep their size, so you won't see any immediate change.
We update the thumbnails on the next visit to the page after 24h though, so they should get updated pretty quickly.

Tested the issue on Windows-10, Ubuntu 14.04 and Mac OS 10.12 using chrome latest Dev M61-61.0.3141.0 by following steps mentioned in the original comment and comment #11. Observed that images are not displaying properly.Please find the screenshot for reference.
Steps Followed:
---------------
1. Install chrome and clear all old thumbnails.
2. visited new sites and open new tab observed that thumbnails are displaying blurry.

@treib: Could you please let me know if i have missed anything and if possible,Please provide the sample test steps of the issue which would help us to verify the issue further.

Thanks in Advance.

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TBH, without a direct side-by-side comparison, I can't tell the difference - it's pretty subtle. Max or Rachel, can either of you tell if the screenshot above is the old, blurry or the new, slightly-less-blurry version?

That said: I don't think this needs any more verification. Max already looked at the new version and was happy with it.

It's hard to say looking at the small screenshot. I checked this on my local machine. The new thumbnails (physical size: 308x92) are sharp and look good. (Marc mentioned that some screenshots that are generated server-side for signed-in users still have the incorrect, old size.)