Re: Interaction of pCAL and gAMA
Glenn Randers-Pehrson <[email protected]>
| Newsgroups | gmane.comp.graphics.png.general |
|---|---|
| Message-ID | <CA+PdXcs7iYsWAa4FnzBP2sw5PJYF+2+mBvsJWe6TjPgZ+3-Uqw@mail.gmail.com> |
The PNG extensions document, which specifies the pCAL chunk, does not address the interaction of pCAL and gAMA. Since the purpose of the pCAL chunk is to relate PNG data to physical values, I think that gamma==1 should be assumed, if there's no gAMA chunk. I'd say that if both are present, it means that the pCAL conversion should be made, then when displaying that, assume that whatever the gAMA chunk says should be used with the already-converted samples. But since the relationship isn't specified, most anything could happen, for example, a viewer could only recognize the gAMA chunk and ignore the pCAL chunk, and the display would not likely be what the author intended. On Thu, Jan 21, 2016 at 5:43 PM, John Bowler < [email protected]> wrote: > Suppose I have a PNG which has *both* pCAL and gAMA. > > Are the stored samples referred to in the pCAL spec the result of gamma > decoding of the IDAT data? > > If they aren't, and I want to store luminance values, I can't see any way > of doing it with pCAL (without producing something that is pretty much > useless as a PNG image). > > -- > John Bowler <[email protected]> > +1 (541) 450-9885 > PO BOX 3151 > KERBY OR 97531-3151 > USA > > > ------------------------------------------------------------------------------ > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. Signup Now! > http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 > _______________________________________________ > png-mng-misc mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/png-mng-misc > > ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ png-mng-misc mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/png-mng-misc