Open Bug 957307 Opened 8 years ago Updated 3 years ago

[HiDPI] Thumbnail previews on new tabs are pixelated


(Core :: Web Painting, defect)

Not set




(Reporter: edwardsgreg, Unassigned)


(Blocks 1 open bug)


(Keywords: regression)


(2 files)

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0 (Beta/Release)
Build ID: 20140107030202

Steps to reproduce:

Set Windows to a DPI above 96 if it isn't already.
Visit some sites to refresh the thumbnails.
Press Ctrl+T to open the new tab window.

Actual results:

Thumbnail previews are pixelated, as if downscaled to 96DPI then up.

Expected results:

Thumbnail previews should be sharp since they are downscaled from their original size.

Firefox 23 shows correct results. Firefox 24 and onward show the pixelated previews. I tested versions 23, 24, 25, 26, and 29. Only Windows is affected; they are sharp on Mac OS X.
Blocks: win-hidpi
Component: Untriaged → Bookmarks & History
Keywords: regression
nothing to do with bookmarks and history, moving to general
Component: Bookmarks & History → General
Blocks: 497543
OS: Windows 7 → Windows
Product: Firefox → Core
Hardware: x86_64 → Unspecified
Version: 24 Branch → unspecified
I wonder whether this is only when the thumbnail was generated for a low dpi window.
Visiting the page in a high dpi window causes the thumbnail to be regenerated appropriately for a high dpi window.
Greg/Karl: Is this still an issue I cannot reproduce this on the latest release
Version 	47.0.1
Build ID 	20160623154057
User Agent 	Mozilla/5.0 (Windows NT 6.1; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0
Flags: needinfo?(edwardsgreg)
It's not as bad as when I reported this bug, but they're clearly still not 1:1 pixels.

Looking at it in Inspect Element, I can easily see that the thumbnail box is 290x180 CSS pixels but the backing image is only 560x380 pixels (not the expected 580x360) which is causing some blurriness.
Flags: needinfo?(edwardsgreg)
Thanks for the update Greg, can you please send me links/urls and I will test some more. Thanks.
Flags: needinfo?(edwardsgreg)
The issue is with the Firefox UI, not any specific site, so I can't exactly provide URLs. The best I can do is give more specific replication steps:

1. Visit various sites in Firefox to populate history so about:newtab will show some thumbnails.
2. Set Windows's DPI to 200% (192DPI).
3. Log off/on to refresh system DPI.
4. Open firefox.
5. Open a new tab or navigate to about:newtab.
6. Observe the thumbnails aren't quite the correct resolution.

If it isn't obvious, right click one of them and choose Inspect Element. The page inspector will report the size of the thumbnail element. (For me, it's 290x180.) The <span> directly above the highlighted one contains the actual image at a moz-page-thumb:// URL. Open it in a new tab to check its size. Observe that its size is 560x380. Since we're using background-size: cover and the aspect ratio is taller than the container, the image is scaled to match the width of the container, so the correct size needs to be 580x360 or taller.)

Curiously, the right side of the thumbnails also appears to be cut off by about the same 20 pixels, but that might be a different bug.
Flags: needinfo?(edwardsgreg)
Attached image DPI_test1.png
Thanks for the clarity Greg,
Reproducible - please see attached screen shots (DPI_test1 and DPI_test2)
Version 	47.0.1
Build ID 	20160623154057
User Agent 	Mozilla/5.0 (Windows NT 6.1; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0
Attached image DPI_test2.png
Ever confirmed: true
Component: General → Layout: View Rendering
Component: Layout: View Rendering → Layout: Web Painting
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