Number of images in a multi-tiff file?

[Mark Pereira]

Hi,

Is there a way to know the number of images present in a multi-tiff file
in constant time.

Currently, I traverse over all the directory entries to determine this,
which is linear.

Thanks,
Mark


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On Wednesday 28 October 2009 20:01:21 Mark Pereira wrote:
> Is there a way to know the number of images present in a multi-tiff file
> in constant time.
TIFFNumberOfDirectories() ?

Brad
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[Frank Warmerdam-2]

Brad Hards wrote:
> On Wednesday 28 October 2009 20:01:21 Mark Pereira wrote:
>> Is there a way to know the number of images present in a multi-tiff file
>> in constant time.
> TIFFNumberOfDirectories() ?

Mark,

No, there is not since the directory list needs to be walked to count them.
The count is not available in a header or anything like that.

Skimming the code briefly it appears that TIFFNumberOfDirectories() is careful
to read the minimum amount of information from the file (a few numbers from
the start of each directory) to count through the file so the cost should
be minimal, but not constant time.

Best regards,
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[Mark Pereira]

Thanks Frank for these clarifications !

Mark

Frank Warmerdam wrote:

Brad Hards wrote:
  

On Wednesday 28 October 2009 20:01:21 Mark Pereira wrote:
    

Is there a way to know the number of images present in a multi-tiff file
in constant time.
      

TIFFNumberOfDirectories() ?
    

Mark,

No, there is not since the directory list needs to be walked to count them.
The count is not available in a header or anything like that.

Skimming the code briefly it appears that TIFFNumberOfDirectories() is careful
to read the minimum amount of information from the file (a few numbers from
the start of each directory) to count through the file so the cost should
be minimal, but not constant time.

Best regards,
  

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