PNG data generated by TkImg1.3

[sachito....@gmail.com]

Recently I implemented TkImg to my application to export screen shot
of BLT graph into a png data. It works quite fine, but I noticed, when
I was working on Windows, that the graphic file seems to be completely
wrong in Image/Fax viewer and MS-Office suite. I can read the file,
but it is fully black.

I tried other applications such as Internet Explorer, GIMP, IrfanView,
PaintShop etc, there is no problem. Once I read the file into these
applications and write it again, the file seems to be normal on the
application with which I had the problem.

I found out that there is a difference between the file directly from
TkImg and the one which I was able to read in MS-Office. Some values
such as gamma, unit, resolution are different. I have read in the
TkImg manual that I might be able to give options to write the file,
but I found nothing.

I am working on many platforms at the same time, I also tried the data
exported by Linux, or SGI platform on Windows, it looks the same. No
other applications seems to have the problem.

I also tried gif format, there is no problem with that.
At the moment I would like to use gif format as standard to avoid this
problem.
However, does anyone have an idea what might be wrong and a workaround
for that, perhaps?

Thank you in advance.

Sachito

[Jeff Hobbs]

sachito....@gmail.com wrote:
> Recently I implemented TkImg to my application to export screen shot
> of BLT graph into a png data. It works quite fine, but I noticed, when
> I was working on Windows, that the graphic file seems to be completely
> wrong in Image/Fax viewer and MS-Office suite. I can read the file,
> but it is fully black.
>
> I tried other applications such as Internet Explorer, GIMP, IrfanView,
> PaintShop etc, there is no problem. Once I read the file into these
> applications and write it again, the file seems to be normal on the
> application with which I had the problem.
>
> I found out that there is a difference between the file directly from
> TkImg and the one which I was able to read in MS-Office. Some values
> such as gamma, unit, resolution are different. I have read in the
> TkImg manual that I might be able to give options to write the file,
> but I found nothing.

I have had similar issues, and I believe that the Windows viewer is
actually one that is slightly different from the rest. I've seen odd
looking corruption as well there that didn't appear elsewhere. This has
happened as well with images written by the GIMP on Linux and then
viewed in the Windows fax viewer.

Jeff

[Paul Obermeier]

Deja Vu,

I noticed this misbehaviour last year, corrected it locally and forgot
about it.

If you compile TkImg yourself, change the following line in png.c
png_set_gAMA(png_ptr, info_ptr, 1.0);
to
png_set_gAMA(png_ptr, info_ptr, 0.45455);

I will also put a correction onto SF TkImg tomorrow.

Paul

[sachito....@gmail.com]

Thank you Jeff, Paul for your precious information,

Jeff, I was also able to imagine that IE and MS-Office suite, Fax
viewer use difference interpretation routine for PNG format. But I did
not know that the file generated by GIMP causes the same problem. It
was really nice to know. I consequently was not able to find any info
by googling.

> If you compile TkImg yourself, change the following line in png.c
> png_set_gAMA(png_ptr, info_ptr, 1.0);
> to
> png_set_gAMA(png_ptr, info_ptr, 0.45455);

Paul, these are the very gamma values I have just seen when I examined
the two different PNG files!!
Our team built TkImg for all 6 platforms by ourselves except Windows.
On Windows we have to build both release and debug version for most of
Tcl/Tk and its extension such as Itcl/Itk, BLT, and Tix, or it won't
work on .NET debugger, I would have often hung-ups.
However, binary distribution of TkTreeCtrl and TkImg seems to cause
any trouble.
And it is also because I was not able to find makefile for VC for
these two extension, actually we just changed our compiler to intel
one for most the platforms as far as it is available on them due to
optimization possibility with external tools. It looks like they are
to provide TEA preferably, but we did/do not plan to use Cygwin in our
environment.
Well, now we are to welcome the code freeze of our products. I
actually noticed this problem when I started to document my feature
changes in release note by using MS-Word. I now think it better that I
would choose the workaround by offering customers GIF as default
format for the screen shot this time. Because customers' wish is to
avoid any other application to get a screen shot.
But I would follow your suggestion for our next major release, it
might be next year, if this change would still have not implemented
yet to TkImg then. Or might be possible to recommend all of our
customers and ourselves to avoid using MS-Office suite in the
office? :-)

I thank again indeed for both of you!
Sachito