Any way to retrieve palette info from an indexed PNG?

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ubernerd

Any way to retrieve palette info from an indexed PNG?

in General Discussion • Other • 1 year ago

I have a unique programming scenario where I am trying to save spectral data in an 8 bit paletted PNG image. This allows me to change the palette to tune the spectral regions to provide emphasis. My problem is that once I have created the PNG, I have no idea if there is a way in Processing to retrieve the indexed palette info to recreate the spectral data as an array.

I can't just query the RGB value per pixel, I need to get access to the palette index. Thanks in advance.

-Mark

Replies(3)

PhiLho

Re: Any way to retrieve palette info from an indexed PNG?

1 year ago

You probably need low level access to the PNG file. Maybe ImageIO can allow this, or JAI, or perhaps even load the image in binary more (loadBytes()) and parse the header. It needs quite some knowledge of the PNG format (chunks and so on)...

ubernerd

Re: Any way to retrieve palette info from an indexed PNG?

1 year ago

Thanks for the help. I figured it would take deeper digging to get the result I need.

ignotus

Re: Any way to retrieve palette info from an indexed PNG?

1 year ago

Maybe the colorLib library by Andreas Köberle and Jan Vantomme will do what you want without mucking around in the palette structure of file. ColorLib doesn't specifically read in a PNG file, but it can generate a palette from a PImage. Very likely the colors in a PImage created from a PNG file are those permitted by the PNG palette.

http://code.google.com/p/colorlib/

HTH,

-- Paul

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