PDFs on HiDPI displays (not multiples of 100%) are blurry (upscaled from 96dpi)
Reported by
jimbo1...@gmail.com,
Feb 14 2018
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Issue description
UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.167 Safari/537.36
Steps to reproduce the problem:
1. Under Windows Settings, change your display scaling ("size of text, apps, and other items") to a non-multiple of 100%. (my display's DPI matches 125% or 150%)
2. Open Chrome.
3. Open a PDF.
What is the expected behavior?
PDF text and images are sharp.
What went wrong?
PDF text and images are fuzzy. I suspect they are rendered under 96dpi and upscaled to my display scaling.
If you zoom in to pdf-100%.png, vertical have exactly 1 pixel of Cleartype transition, and character baselines are grid-aligned.
If you zoom in to pdf-175%.png, you'll see vertical lines are several pixels wide, but character baselines are still grid-aligned for some reason.
Did this work before? No
Chrome version: 64.0.3282.167 Channel: stable
OS Version: 10.0
Flash Version:
Entering fullscreen mode may or may not native-resolution rendering.
Last time I checked (months ago), changing my display scaling to exactly 200% produces sharp rendering.
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Feb 16 2018
Unable to reproduce the issue on reported chrome version 64.0.3282.167 and on the latest canary 66.0.3347.0 using Windows 10 HighDPI laptop(EliteBook) with the below mentioned steps. 1. Launched Chrome 2. Changed Display scaling to 250, as mentioned to use a non-multiple of 100. 3. Navigated to http://www.pdf995.com/samples/pdf.pdf We are able to see the PDF text sharp with out any blur. Attaching the screen shot of the same. @Reporter: Could you please check the screen shot and let us know if we have missed any steps while reproducing the issue. It would be highly helpful if shared with the test file in which the issue is seen. Thanks!
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Feb 16 2018
Zooming in using ShareX Ctrl+PrintScreen, I noticed in your screenshot that character bottoms are not aligned to the pixel grid. I tried zooming in really far, and it seems to happen at the same size when subpixel colored rendering turns off (DWRITE_RENDERING_MODE_OUTLINE turns on?) Personally I hate how sharpness decreases for big text, but that's not this issue. This bug concerns DPI*zoom factors below where grayscale rendering (DWRITE_RENDERING_MODE_OUTLINE) begins. Can you try using something below 200% and not zoom into the PDF?
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Feb 16 2018
Thank you for providing more feedback. Adding requester "vamshi.kommuri@chromium.org" to the cc list and removing "Needs-Feedback" label. For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot
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Feb 16 2018
Looking carefully at 175%, I noticed that vertical lines are usually smeared across 2 pixels of (colored) non-black-or-white pixels, while horizontal lines are still grid-aligned or have 1 pixel of gray. ("DOWNLADING" G's top ends in a near-horizontal line. I thought I saw two rows of grays, but Paint eyedropper showed otherwise.).
I suspect that subpixel rendering (does PDFium use ClearType?) is smearing vertical edges across 1 pixel-width at 96dpi, producing widened color smudges since the actual image is higher resolution. As an experiment, I turned off Windows Cleartype but PDFium used subpixel rendering anyway.
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Feb 28 2018
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May 26 2018
bsep / robliao: Can you confirm this bug? I don't have a HiDPI monitor. Controlling cleartype is bug 91959, BTW.
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Jun 21 2018
@robliao@chromium.org and bsep@chromium.org: Could you please confirm the issue as per comment #7 and adding Needs-Feedback to it. Thanks.!
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Sep 18
Finally got around to trying this. I think I see the fuzziness. I have not looked in detail, but the theory that it is rendered at a lower DPI and then upscaled is plausible.
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Nov 23
*** Mass UI Triage *** We were unable to find repro steps for this bug. If you have more data to reproduce this bug or have clear repro steps, please reopen or file a new issue. Thanks!
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Nov 23
This issue has been ignored for nearly a year, and has been wrongly closed as "unable to reproduce". To the contrary, the issue is perfectly real, I supplied instructions in the first post and suggested using ShareX to zoom in on the individual pixels, and thestig@chromium.org has reproduced the issue (but ignored it afterwards). Version 70.0.3538.110 (Official Build) (64-bit) http://www.pdf995.com/samples/pdf.pdf I have attached a screenshot showing: - vertically-blurred vertical stem ends: - - The bottom of "filp"... is blurry, unlike at 100% DPI. - Lots of 2-pixel-wide Cleartype fringes on vertical stems. From left to right: - - Light orange, dark orange, dark blue, light blue. - This may or may not be present in sharp Cleartype (I counted 3 fringes on some characters in the URL bar), but nonetheless text appears much fuzzier at 125% than 100%. Compare to the windows=100 screenshot, where all "filp" have sharp bases, and all text feels sharper. If you cannot see the lightly colored fringes, try using an image editor's Curves tool to decrease the brightness of grays.
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Nov 23
If you want, I can perform a 2D Fourier analysis of these images to see if high-frequency information is missing or replaced with an alias of lower-frequency data.
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Nov 27
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Dec 23
1.7x vs 2x-scaled Chrome @ 2160p, I observed the same blurriness on Linux Chrome 71.0.3578.98 and Windows Chrome 73.0.3642.0 |
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Comment 1 by manoranj...@chromium.org
, Feb 15 2018