Re: Encoding PNGs without gAMA

[Peter Becker]

Thomas DeWeese wrote:

Peter Becker wrote:

Me again,

I should first try then talk. I managed to get the results I wanted 
but there are some small issues.

(a) it might be better to use transcoding hints instead of the extra 
contructor. If I understand the code right it would be consistent to 
set a mapping from something like KEY_PNG_ENCODING_PARAMETERS to the 
parameter object.


  It would certainly be more consistent to use a hint.  Although this is
a _very_ specific hint - so it might not matter that much.
(b) there is actually a KEY_GAMMA used in the code. It just doesn't 
work since the transcoder always declares sRGB as intentional and 
that has the consequence of turning gamma on. Somehow this 
combination of offering KEY_GAMMA as hint and _always_ assuming sRGB 
is intentional seems inconsistent to me


  I agree, this is a bug.  What I have done is:
If KEY_GAMMA is not present or is 2.2 just set sRGBIntent.
else If KEY_GAMMA is == '0' don't generate gamma chunk do generate
   cHRM (with default sRGB value) chunk.
else don't output sRGBIntent but output gamma (with given value) and
   cHRM (with default sRGB value) chunks.
I'll deliver this later today.  This should let you do what you want.

Sounds good to me. I was thinking along giving more options by offering 
tweaking the whole parameter set, but I suspect that might be overkill.

Two little questions from someone not really knowing about PNG: is there 
absolutely no situation you might want to set a 2.2 gamma without 
wanting sRGB? And won't you have the same problem as the spec that 2.2 
might not always be the same as 2.2 -- e.g. if someone cast a float to a 
double? Just try this:

 System.out.println(2.2 == 2.2f);

Intuitively I'd skip the extra rule for 2.2 -- no gamma given is already 
sRGB. Two ways to achieve the same seem to just create confusion -- esp. 
if one of the methods might not always work.

But in any case that wouldn't affect me :-)

 Peter

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