1782877 - canvas.toDataURL("image/webp", 1.0); not properly implementing LOSSLESS webp

Status: RESOLVED FIXED

(Core :: Graphics: Canvas2D, defect)

Description

[stephen.ehlers]

Attachment: LosslessExample.html

Steps to reproduce:

1. Build Graphic with canvas rendering 2d context.
2. Grab raw bytes from getImageData.
3. Call canvas toDataUrl("image/png", 1)
4. Populate an image element src with the url;
5. Use the image as the source to for a drawImage call on a 2d context.
6. Grab raw bytes from png sourced rendering by doing a second getImageData call on your 2d context.
7. Compare original bytes to lossless png bytes (success).

Repeat 1-7 but on step 3 instead use toDataUrl("image/webp", 1) .

Actual results:

The byte comparison for PNG and the Original bytes match 100%, meaning it was truly a lossless conversion.

The byte comparison for WebP will show mismatches, meaning that the conversion had data loss.

Expected results:

Both PNG and WebP formats with a quality/precision or 1 (lossless) should result in identical bytes to the original image.

Comment 1

[stephen.ehlers]

Expected results should say "of 1" not "or 1".

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Graphics: Canvas2D' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 3

[Timothy Nikkel (:tnikkel)]

Attachment: Bug 1782877. Encoding webp with quality 100 should use lossless. r?aosmond,lsalzman

Chrome and Safari do, and it makes sense.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cc6e6cb510c5
Encoding webp with quality 100 should use lossless. r=aosmond

Comment 5

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/cc6e6cb510c5