JPG to PNG with transparent border

[christianjules]

Hello,

I would like to convert a JPG to PNG, adding borders at the left and right and making them transparent. I am trying to do that with this command :
nconvert -out png -canvas 300 300 top-center -transpcolor 0 0 0 -merge_alpha 9781895526066.jpg

But I only get two black borders, not transparent. Could someone tell me what is wrong in my commande line, please ?
The original JPG and the PNG I get are attached.

Btw, I use NCONVERT v6.17 for MacOS X (10.8.2)

Regards,
Christian

[christianjules]

Too bad no one seems to have the same need ...
I have also tried to split it in two separate taks : jpg -> png a first, then adding the transparency with -transpcolor, but I obtain the same result : my black borders are not transparent.
Regards,
Christian

[xnview]

Please try

Code: Select all

nconvert -out png -32bits -bgcolor 255 0 0 -canvas 300 300 top-center

[christianjules]

It works, great !
But what was wrong in my commande line ? I thought the -transpcolor parameter was the appropriate one ...
And also, is the color 255 0 0 pre-defined to be the transparent color pour PNG32 ?
Anyway, thanks a lot for your help.

[xnview]

It works, great !
But what was wrong in my commande line ? I thought the -transpcolor parameter was the appropriate one ...
And also, is the color 255 0 0 pre-defined to be the transparent color pour PNG32 ?
Anyway, thanks a lot for your help.

-bgcolor has a little problem, if you use -bgcolor 0 0 0 it doesnt work...

[DOS386]

http://newsgroup.xnview.com/viewtopic.php?t=12247

> But what was wrong in my commandline ?

" -32bits" converts 24 bpp to 32 bpp ... but ...

> I thought the -transpcolor parameter was the appropriate one

It should be sufficient ... but does't work for 24 bpp (PNG can, NC can't ... BUG or missing feature) ?

> And also, is the color 255 0 0 pre-defined to be the transparent color pour PNG32 ?

There is no "transparent color pour PNG32" ... transparent RGB color is used only in 24bpp PNG, and it's NOT set to 255 0 0 by PNG spec: http://www.libpng.org/pub/png/spec/1.2/ ... tml#C.tRNS

Note that you have to remove any possible (0,0,0) values (replace them by (0,0,1)) before adding transparency based on a transparent color (0,0,0) ... what's the best way with NC ???

> -bgcolor has a little problem, if you use -bgcolor 0 0 0 it doesnt work...

Works for me (NC 6.17) But shouldn't "-bgcolor" eat 4 instead of 3 numbers for 32bpp images ?

And "-transpcolor" is either broken or I don't know how to use it.