Re: [png-mng-implement] [png-mng-announce] Release of libpng-1.5.0

[Alexander S. <ale...@gm...>]

On Mon, Jan 10, 2011 at 18:23,  <jb...@ac...> wrote:
> From: Alexander Shulgin [mailto:ale...@gm...]

Sorry for the delay in response.

>>All these failing tests have something to do with input transformation from 16-bit RGB(A) image to 8-bit grayscale (+Alpha).
>
> Are you setting a screen gamma?

No.

>>How can I check that?
>
> The easiest way is to bring up all three images (original, old output, new output) and compare the pixel values by hand.  The few hex encoded values I looked at in your window were different by 1, and I think it's 1 in the LSBit.  If gamma correction is being done then insignificant changes in the 16 bit calculations are expected and these can, and do, cause significant changes when converted to 8 bit because digitization to 8 bits is losses perceptual information (i.e. 8 bit isn't accurate enough.)
>
> Can you send me the output images (old and new) from basn2c16.png plus the transforms you set (actually, screen gamma is enough if you set it?)

Please find attached output images along with source code to produce
them.  out-lp14.png is produced when linking with libpng-1.4.4, -lp15
-- with libpng 1.5.0.

--
Alex