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RE: pngread does not read 12bit gray images
From: |
de Almeida, Valmor F. |
Subject: |
RE: pngread does not read 12bit gray images |
Date: |
Wed, 16 Jul 2008 18:49:44 -0400 |
> -----Original Message-----
> From: Bill Denney [mailto:address@hidden On Behalf Of Bill Denney
> Sent: Monday, July 14, 2008 6:54 PM
> To: address@hidden; de Almeida, Valmor F.
> Subject: Re: pngread does not read 12bit gray images
>
> I assume that you meant to send this reply back to the list. If not,
Thanks for putting it back. Here are some comments for the record.
> > That is fine. But the user should have the option of doing this 0-1
> scaling from integer to double on his/her own.
> >
>
> Hopefully it's not actually converting to a double (I would view that
as
> a real problem).
I misunderstood your past e-mails when you mentioned 0-1 scale.
> Having done scientific image analysis before, I realize that the work
is
> often low contrast and that it is necessary to keep all information
> intact. I would argue that putting 774 into a uint16 is not keeping
all
> information intact while putting the bits that make up 774 into the
> leftmost bits of a uint16 is keeping the information intact and
> corresponds to what most image processing/manipulation tools expect.
I guess I care about what happened to my $774; that is, this "tangible,
buying-power quantity" which is represented as
774 on the decimal base system and,
0000001100000110 on a big-endian 16-binary base system.
If it happens that it has been bit shifted to the left by 4 instead, I
would certainly welcome that because now
0011000001100000 represents
$12384 and that is certainly a financial advantage :)
Thank you for pointing this out. I currently read 12-bit png images as
follows
Y = __magick_read__(filename);
Y = bitshift(Y,-4);
and this matches the info from running imagemagick identify on the file.
imread() should not be used if you have libpng on your system because
this will call a reader that converts the 12-bit data to 8-bit data, and
that is not good.
I have also loaded the file with cinepaint and verified that internally
the pixel values have been shifted to the left by 4 as you mentioned.
Thanks,
--
Valmor
- pngread does not read 12bit gray images, de Almeida, Valmor F., 2008/07/05
- Re: pngread does not read 12bit gray images, Søren Hauberg, 2008/07/06
- RE: pngread does not read 12bit gray images, de Almeida, Valmor F., 2008/07/11
- RE: pngread does not read 12bit gray images, Søren Hauberg, 2008/07/11
- Re: pngread does not read 12bit gray images, Bill Denney, 2008/07/11
- Re: pngread does not read 12bit gray images, Søren Hauberg, 2008/07/11
- RE: pngread does not read 12bit gray images, de Almeida, Valmor F., 2008/07/11
- Message not available
- Message not available
- Re: pngread does not read 12bit gray images, Bill Denney, 2008/07/14
- RE: pngread does not read 12bit gray images,
de Almeida, Valmor F. <=
- RE: pngread does not read 12bit gray images, John W. Eaton, 2008/07/16
- RE: pngread does not read 12bit gray images, Søren Hauberg, 2008/07/17
- Re: pngread does not read 12bit gray images, Bill Denney, 2008/07/17
- Re: pngread does not read 12bit gray images, Søren Hauberg, 2008/07/20
- RE: pngread does not read 12bit gray images, de Almeida, Valmor F., 2008/07/17
Re: pngread does not read 12bit gray images, Bengt-Arne Fjellner, 2008/07/10