Re: Writing image to blob PNG vs TIFF

On Mon, 18 Dec 2017, Robert H. Olsen wrote:
>
> I think I'm probably misunderstanding what you mean by "multiple image 
> frames" though?

Probably I provided an answer for a different question. :-)

The TIFF format supports multiple frames per file and PNG does not. 
But that is apparently not what you are doing.

I don't know what your GetPBlob() function does.

I would expect that there is a new memory allocation in the Blob 
object for each image write and the existing allocation is freed. 
The Blob object can support memory allocated via malloc() or C++ 
'new'.  The C code can only allocate memory via malloc().  Each image 
written might require a different size allocation.

I would hope that the Blob does not need to be empty in order to be 
written on.  I would also hope that there is nothing stateful about 
writing TIFF files so it only works once.

> I'm only interested in dealing with a single image at a time - not, for 
> example, making a multiple-image TIFF.  I want to capture an image, process 
> it, package it, send it out over the network and then wait for another.  And 
> this works fine if I tell Image.write that it's a PNG.  Is there some way of 
> saying "this is a new, distinct image" when writing TIFF to a blob, other 
> than changing its size? Would toggling between two different pBlob memory 
> locations trick it?

I am not sure what the problem is and do not have time to try to 
replicate the issue.  It is useful to master the tracing.  It appears 
that Magick++ does not currently offer functions to control the 
tracing.  The tracing can be controlled via the MAGICK_DEBUG 
environment variable.  The value string useful for MAGICK_DEBUG is the 
same as the command-line -debug option:

       -debug <events>
               enable debug printout

               The events parameter specifies which events are to be
               logged.  It can be either None, All, or a comma-sepa‐
               rated list consisting of one or more of the following
               domains: Annotate,  Blob,  Cache,  Coder,  Configure,
               Deprecate, Error, Exception, Locale, Render,Resource,
               TemporaryFile, Transform, Warning, X11, or User.  For
               example, to log cache and blob events, use

                   gm convert -debug "Cache,Blob" rose: rose.png

You could use "Blob,Coder,Exception" to learn quite a lot about what 
is going on.  The word "All" also works in order to enable everything.

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

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