322647 - drawImage from canvas darkens image

Status: RESOLVED WORKSFORME

(Core :: Graphics: Canvas2D, defect)

Description

[Christopher Clay]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20051111 Firefox/1.5
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8) Gecko/20051111 Firefox/1.5

When using a canvas as the source for drawImage, the lightness seems to be very slighly decreased in the resulting image.

This happens regardless whether the source is another canvas or the target itself. Doing clearRect on the target before drawing does not help. 
globalAlpha or globalCompositeOperation are not set.

Reproducible: Always

Steps to Reproduce:
Fill a canvas with white, copy it to itself repeatedly using context.drawImage(canvas, 0, 0)
(will attach testcase that does this)
Actual Results:  
Canvas slowly fades to black

Expected Results:  
Canvas remains white

Comment 1

[Christopher Clay]

Attachment: testcase

Comment 2

[Peter van der Woude [:Peter6]]

Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9a1) Gecko/20060111 Firefox/1.6a1 ID:2006011113

Confirmed

Comment 3

[Kathleen :Brade]

This also seems to be a problem in drawWindow().

On Linux, with a 16-bit depth display, drawWindow() doesn't produce color values that are perfectly correct.  For example, white (255,255,255) pixels in the original window are rendered on the canvas as (248, 252, 248).  Solid yellow becomes (248,252,0).

Reassign to roc per irc conversation.

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I think the drawWindow issue is different.

I'm not 100% sure what's going on here. Does a white image drawn to the canvas darken at all?

Comment 5

[Christopher Clay]

drawImage using a white HTMLImageElement as a source produces a perfect result, but drawImage using a HTMLCanvasElement that is painted with rgb(255, 255, 255) as the source produces rgb(254, 254, 254).

(Thus when you wait until the counter says 255 in the test case, you'll have perfect black -- I hadn't noticed that before. Btw, the ColorZilla extension with its color picker is very useful for testing this)

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Are you using a 16-bit or 24-bit display?

Comment 7

[Hermann Schwab]

(In reply to comment #6)
> Are you using a 16-bit or 24-bit display?

Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.9a1) Gecko/20060107 SeaMonkey/1.5a
I'm seeing this on a 16-bit-display, 800x600, SiS6326 graphics card 8MB

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I want to know if this happens on a 24-bit display.

Comment 9

[Hermann Schwab]

(In reply to comment #8)
> I want to know if this happens on a 24-bit display.
 
Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.8) Gecko/20051111 Firefox/1.5
Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.9a1) Gecko/20060107 SeaMonkey/1.5a
Now seeing this on a 24-bit-display, 800x600, SiS6326 graphics card 8MB

Comment 10

[Peter van der Woude [:Peter6]]

this bug happens with all,

I use 32-bit
Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9a1) Gecko/20060112 Firefox/1.6a1 ID:2006011212

Comment 11

[nemo]

The results with a globalAlpha of 0.5 or less are odd.
http://m8y.org/tmp/drawimagetest.html

Comment 12

[Christopher Clay]

Appears to work fine in Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1a3) Gecko/20060526 BonEcho/2.0a3 -- propose resolving it as FIXED if someone can confirm?

Comment 13

[Peter van der Woude [:Peter6]]

Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.9a1) Gecko/20060529 Minefield/3.0a1 ID:2006052910 [cairo]

confirmed, testcase stays white
since we don't know what fixed it -> WFM