Re: [Openexr-devel] Modifying an attribute

[Florian Kainz]

Brad Hards wrote:
> Is there a standard (safe) way to modify the attribute in a file on the disk?
>
> Is it going to be a matter of reading the whole file, modifying the attribute 
> and writing the whole thing back out?
>
> Brad
>
>
> _______________________________________________
> Openexr-devel mailing list
> address@hidden
> http://mail.nongnu.org/mailman/listinfo/openexr-devel


Hi Brad,

because modifying an attribute can change its size, there
is currently no way to modify an attribute in place, without
rewriting the file.
However, the IlmImf library does support a copyPixels()
function that copies from one file to another without
uncompressing and re-compressing the pixels.  Using this
function, changing an attribute is takes about as long as
as simply copying the file.
The code snippet below (adapted from the exrstdattr utility)
inserts a string attribute into a file's header.  If an
attribute with the same name exists already, it is replaced.

Florian

---

    InputFile in (inFileName);
    Header header = in.header();

    header.insert ("foo", StringAttribute ("bar");

    if (header.hasTileDescription())
    {
        TiledOutputFile out (outFileName, header);
        out.copyPixels (in);
    }
    else
    {
        OutputFile out (outFileName, header);
        out.copyPixels (in);
    }