Re: Writing image to blob PNG vs TIFF

On Mon, 18 Dec 2017, Robert H. Olsen wrote:
>
>   // Create a formatted gm blob
>   Blob * pBlob = GetPBlob();   // points to space allocated elsewhere
>   gmimage.write(pBlob, GetGMType());  // GetGMType() returns either "PNG" or 
> "TIFF"
> //   gmimage.write(pBlob, "TIFF");
> //   gmimage.write(pBlob, "PNG");
>
> This works well for "PNG" but if the type is "TIFF" then the image at pBlob 
> is correct only the first time through after starting up or changing from PNG 
> mode, or if I change the number of times minify() is run on the image, 
> otherwise the image data is not changed though it should have been updated 
> when the new trigger was received. If I switch back to PNG everything is fine 
> again.  Do TIFF and PNG deal with previously allocated space differently, or 
> something like that?

Due to my decision to use STL containers to support multiple image 
frames, the Image read/write functions only support a single image 
frame.

You must use the STL-based interfaces readImages() and writeImages() 
from Magick++/STL.h to deal with multiple frames.

Please see http://www.graphicsmagick.org/Magick++/STL.html for 
documentation on how to use the STL-based interfaces.

Unfortunately, this means that some of your code will need to be 
re-written.

At the C language level, a sequence of image frames is represented by 
a linked list.  For the C++ interface, these sequences (based on 
previous/next pointers) are broken (previous/next pointers set to 
NULL) and the STL container functionality is used to remember the 
relationship between frames.  When the C++ interface calls into the C 
interface it must temporarily re-create a linked list of image frames 
(which it again destroys afterward).  For this reason, you should not 
use multiple threads on the same STL container.

Bob

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