920957 - Image upscaling quality: Text in images loses contrast more than in Chrome.

Status: UNCONFIRMED

(Core :: Graphics: ImageLib, defect)

Description

[yu_icq]

Attachment: Side-by-side comparison of image scaling in chrome and firefox. Source is misfile.com

User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.76 Safari/537.36

Steps to reproduce:

Go to www.misfile.com/?date=2013-09-26.
Zoom in (most obvious at around 150%). 


Actual results:

Image looks unclear compared to equivalent zoom level in Chrome (see attached screenshot comparison). More specifically the image looks bright and low on contrast, diagonal lines look slightly jagged, while neither occurs in Chrome.

The result was the same with Firefox 23, Firefox 24 and Nightly 27.0a1 (2013-09-25). 

Setting gfx.color_management.mode to zero (see https://bugzilla.mozilla.org/show_bug.cgi?id=501505) and disabling hardware acceleration did not change the result.


Expected results:

Scaling should preserve the readability of text inside images when zooming in. 

The effect creates a "lower quality" feeling on webpages in general, and makes specifically text in images (as in webcomics) harder to read.

Comment 1

[Loic]

Could you test if there is a difference with image.high_quality_downscaling.enabled=false (restart the browser).

Comment 2

[yu_icq]

Attachment: Side-by-side comparison v2 (misfile.com)

With image.high_quality_downscaling.enabled=false the contrast issue is improved (see first row), but still Chrome gives the better readability (see second row).

For highlighting the differences a bit more I have also included subtractions of the new screenshots. 

At 100% zoom the images are pixel-equivalent (checked just in case that Chrome applies some filters even without scaling, e.g. color profile issues).

Comment 3

[yu_icq]

Attachment: Side-by-side comparison v3; Pseudocolor image of the brightness/blurryness difference added