What is wrong with PNG with Alpha mask ? Everything it seems

[gilesgoat]

So "here we are again" .. any time I get "something different" ..

So suppose someone ( probably made on MAC not sure ) gives you "a high res PNG of a logo" with a transparent alpha mask.

So like "BANANA" on a transparent background.

You say "where's the problem to import it into anything" .. well suppose you'd like to save that PNG maybe "in some other format" with an alpha channel ..

"Sure how hard can it be ?" ..

FUCKLOAD .. it seems .. "i've seen ALL sort of crap" coming out from programs trying to convert a PNG with a transparent layer into something else, let's say "the simplest as possible" an RGBA32 .tga or such .. you think where is the problem, you have 24 bits for RGB and 32 bits for Alpha .. "a snap" ..

NO ...

To make it short "every damned program I used" seems to have "a different idea" about what "alpha" should be ...

It's a mess .. a terrible mess ...

[Oaf]

Paint.net

[Little stoned kiwi]

Gimp?

But then, why?

[gilesgoat]

Gimp?

But then, why?

I have Gimp.

I don't know how someway someone managed to send me a "texture" that "looks so stupid" and must have something that as soon as I try to convert it into something else goes all crap .. I really don't know "how it's possible to fuck up such a simple thing" ??

[gilesgoat]

So in the end I actually used GIMP, I re-opened that file, scaled it down just a little and re-exported as DDS.

This time it did work ...

Do I know what the heck had it before ? NO and I will NEVER know !

[gilesgoat]

"More shit with PS4" this time ..

Apparently "certain programs" may embed some "metadata" in the .PNG that NOT everyone likes ...

"Put this image 1024x1024 24Bpp here" .. SOUNDS .. trivial .. NO IT ISN'T !

<Process>...
"Error : Image is not in a valid format !"
</Process>

NNNNNGGGH !

One day I have to read the PNG specs, for curiosity, I know that PNG supposedly "it's better for hand drawn/comic/sharp edges images" so I am not sure what type of compression, other than DCT/etc. uses but I suppose "something else".

Or was it just invented to circumvent some patent issues ?

[Vargol]

From what I remember PNG takes the first value in a row then generates deltas for the rest then does uses one of the patent free standard compression algorithms.
on the row. Throw in a CRC32 value of the compressed data I think and a header. Not sure how it splits up the RGBA though.

It can do columns and diagonals etc to derive the deltas too, but each chunk is row

I've written a noddy Java (and .net I think?) class that used a subset of the deltas method, but thats was greyscale so I didn't have to split the RGB
Looked up the code, mostly right, the compression is zlib.

[rowan]

I use pngout to optimise [compress] png files.
It also strips unnecessary chunks by default, at a guess that may sort out what PS4 doesn't like.

Tutorial
http://advsys.net/ken/util/pngout.htm

Executable
http://advsys.net/ken/utils.htm#pngout