#7 bug in Tux Paint alpha calculation

v0.9.14_(ALL)
closed
nobody
Rendering (4)
6
2012-10-03
2004-10-25
William Kendrick
No

I think you're operating on gamma-modified data
when you should be operating on linear-light data.

Consider a background of 0x40 grey (sRBG color space),
with an object of 0xc0 grey, and an alpha of 50%. The
result should not be 0x80 grey; that would be too dim.

To avoid round-trip losses, 16-bit intermediate channels
may be required.

The above is based on seeing significant dark fringes
around an image that shouldn't have more than a tiny
bit, if any.

(Ref: Private email to Bill K. from Albert C., 2004-10-25)

Discussion

  • Logged In: YES
    user_id=132410

    I believe these were implemented by Albert in Tux Paint
    0.9.15. (Please re-open if not!)