Bug 38735 – ImageBuffer::transformColorSpace : linear RGB -> sRGB conversion formula error

• Status: RESOLVED
• Resolution: FIXED
• Component: SVG

[Zoltan Herczeg]

let f(x) = ((x + 0.055) / 1.055) ^ 2.4

f(x)^(-1) (inverted formula) is ((x ^ (1 / 2.4)) * 1.055) - 0.055
instead of ((x * 1.055) ^ (1 / 2.4)) - 0.055

[Zoltan Herczeg]

Created attachment 55357 [details]
patch

[Zoltan Herczeg]

Created attachment 55359 [details]
Updated ChangeLog

[Darin Adler]

Comment on attachment 55359 [details]
Updated ChangeLog

> +                color = (pow(color, 1.0f / 2.4f) * 1.055f) - 0.055f;

Shouldn't this be powf? Using pow means we'll convert to double and then back to float.

[Zoltan Herczeg]

Created attachment 55458 [details]
change pow to powf

Darin, nice catch.

[Dirk Schulze]

(In reply to comment #3)
> (From update of attachment 55359 [details])
> > +                color = (pow(color, 1.0f / 2.4f) * 1.055f) - 0.055f;
> 
> Shouldn't this be powf? Using pow means we'll convert to double and then back
> to float.

Right, sorry. Didn't see  that.

[Nikolas Zimmermann]

This does not affect mac pixel tests?

[Dirk Schulze]

(In reply to comment #5)
> (In reply to comment #3)
> > (From update of attachment 55359 [details] [details])
> > > +                color = (pow(color, 1.0f / 2.4f) * 1.055f) - 0.055f;
> > 
> > Shouldn't this be powf? Using pow means we'll convert to double and then back
> > to float.
> 
> Right, sorry. Didn't see  that.

No it doesn't. The code is just used for Chromium Gtk and Qt.

[Zoltan Herczeg]

Landed in r59002 : http://trac.webkit.org/changeset/59002

Closing bug.