I'd expect that the error might not accumulate for most color values.
Rounding would potentially kick in once you get the first loss of
precision. I've only historically seen color shifts upon repeated
rendering in scenarios where you're losing lots of precision, or
losing energy (bad RGB <-> HSV conversions, for example) - you don't
actually need a lot of precision to fix that as long as your
coefficients are right.

On Fri, May 16, 2014 at 8:41 PM, Rik Cabanier <caban...@gmail.com> wrote:
>
>
>
> On Fri, May 16, 2014 at 3:06 PM, Justin Novosad <ju...@google.com> wrote:
>>
>> On Fri, May 16, 2014 at 5:42 PM, Rik Cabanier <caban...@gmail.com> wrote:
>>>
>>>
>>> Is the Web page not composited in sRGB? If so, it seems the backing store
>>> should be sRGB too.
>>>
>>
>>
>> The web page is not composited in sRGB. It is composited in the output
>> device's color space, which is often sRGB or close to sRGB, but not always.
>> A notable significant exception is pre Snow Leopard Macs that use a gamma
>> 1.8 transfer curve.
>> By the way, sniffing the display color profile through getImageData is a
>> known fingerprinting technique. This factor alone can be sufficient to
>> fingerprint a user who has a calibrated monitor.
>
>
> I'm unable to reproduce what you're describing. So, if I fill with a color
> and repeatedly do a getImageData/putImageData, should I see color shifts?
>

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