Re: Image Manipulation problem

On Fri, 15 Apr 2005, Jason Heblack wrote:

>> I suggest that you try changing your CharPixel read into a simple read 
>> from a file name.  See if the problem then goes away.  If the problem goes 
>> away, then that means there is some bug in the CharPixel reader. This will 
>> help me diagnose what the problem may be.
>
> Yeah, reading from a file name and then calling an image manipulation 
> function works but there is a problem displaying it afterwards.  If the new 
> image is saved to a regular file then there is no problem.  The problem seems 
> to be writing to and reading to an unsigned char array inside my program so 
> that my program can display the new image data with it's own image display 
> functions.  If there is no image manipulation, the CharPixel data array 
> displays fine but if there is a manipulation performed then the new image 
> will not display on the screen.  If saved to a file it will appear mangled.

It is most likely that this failure is occuring due to a bug elsewhere 
in your program.  A common problem is double frees, or freeing memory 
addresses which are not allocated, continuing to update memory after 
it has been deallocated, or writing outside of an allocated area.  On 
some systems, these problems are noticed right away, but on some 
others (e.g. Solaris) the program eventually dies in an unrelated 
area.

These problems could be blamed on GM, but it is worth mentioning that 
GM 1.1.X's entire test suite has been run under valgrind on Linux. 
When we first started running GM under valgrind, thousands of errors 
were reported due to problems in hundreds of places.  Now there are no 
more errors reported.  It took two months of work to get to that 
point.

There is a test program which tests the interfaces you are using.

If you can provide a tiny, portable (e.g. based on iostreams or 
stdio), test program which demonstrates the bug, then I can fix it.

Bob
======================================
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/


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