FPReaderPNG doesnt read 16bit Gray (single channel) PNG files
lazarus / 39-Graphics

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CorBee · 2014-11-19 20:02

Hi,

I am developing an application where I need to be able to read 16bit
single channel gray PNG images. The FPReaderPNG does allow me to read
the images but the data that I get from the images is only the upper 8
bits of the 16bit data. Other 16bit PNG files do work as planned.

Anybody with an idea where to fix this ?

kind regards
CorBee
*************************************************
RegiStax Free Image Processing Software
http://www.astronomie.be/registax
*************************************************

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Timewarp · 2014-11-19 20:25

http://bugs.freepascal.org/view.php?id=24382

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CorBee · 2014-11-19 20:40

Thanks. So an unresolved issue ..

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Timewarp · 2014-11-19 21:03

Quote from: CorBee on November 19, 2014, 09:40:58 pmSo an unresolved
issue ..And expected to remain (unless someone commits the patch)

BGRABitmap has this fix included.

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CorBee · 2014-11-19 21:29

In BGRABitmap I see this routine
function TBGRAReaderPNG.ColorGray16 (const CD:TColorDAta) : TFPColor;
var c : NativeUint;
begin
  c := CD and $FFFF;
  with result do
    begin
    red := c;
    green := c;
    blue := c;
    alpha := alphaOpaque;
    end;
end;

Thats no different from the routine in FPreadPNG.

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Timewarp · 2014-11-19 21:52

Problem is in ColorGrayAlpha16
Are you sure your images don't have alpha?

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CorBee · 2014-11-19 22:02

Unfortunately I cant access the part where the FPreadPNG gets the info
on the format. That info is not accessible during the loading in
Lazarus.

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CorBee · 2014-11-21 14:31

Ive switched to the Vampyre Imaging Library ... turns out that the
file was Gray16 without alpha.

regards
Cor

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Timewarp · 2014-11-22 11:04

Can you attach sample png?

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CorBee · 2014-11-22 11:06

The images are 3Mb in size, does the forum allow that ?

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circular · 2014-11-22 12:44

You can put a link to Dropbox, GoogleDoc...

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CorBee · 2014-11-22 13:45

Try this
https://www.wetransfer.com/downloads/f9f99e5cdf9197bf23475a8fc7c152a62
0141122134233/1e0194152a26ae3aeef98d95232f05e320141122134233/cd666b

or

http://we.tl/sifb0a2dU3

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marcov · 2014-11-22 13:46

Quote from: Timewarp on November 19, 2014, 10:03:25 pmQuote from:
CorBee on November 19, 2014, 09:40:58 pmSo an unresolved issue ..And
expected to remain (unless someone commits the patch)

BGRABitmap has this fix included.

It has been waiting for sb to do a thorough investigation for some
time now.

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circular · 2014-11-22 14:24

The image seems to load well with BGRABitmap. It is 16-bit grayscale
without alpha.

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CorBee · 2014-11-22 14:32

Good to hear that, I am using the Vampyre library currently. It would
be nice to have a library that can read all the 16bit formats