How much time should it take ideally to convert PNG to TIFF?

[rishabh]

Hi,
I am using 6.6.6 version on imagemagick in c++. I use this application to convert PNG TO TIFF(Bilevel monochrome) format with FAX4 compression.
The size of image is 3300x2550 pixels and DPI is 300. Earlier when I use IM back in 2013 the conversion rate was 1 sec per page avg (max 2sec).
But now I see a large performance degradation say it takes around 8 sec+ per page. I am performing various actions on it say annotation adding redaction,resizing etc but same as 2 years back.
I want to understand this very well why this is happening (what are the possibilities)because I never changed the version of ImageMagick .
Few of my questions and informations are :
1. what are the actions which make the image.write(path) operation too long?
2. How can I achieve the same performance?
3. Monochrome image should be the fastest conversion as PaletteType image grayscale true color takes much longer.
4.I am using threshold operation in order to rectify image does that makes performance bad because after removing threshold operation the pages starts taking 16 sec.
5.I AM USING 16GB RAM 3 ghz Octacore processor . So hard ware should not be a problem.
6.Reading and writing operation are happening in same folder where the code runs.
7.I am using c++ APIs of image magick.
8.What are the cases where I can do the conversion at same speed without degradation of quality.?

Please can some one throw light on the possibilities to attain the same performance or where I am going wrong because action previous and now remains the same without change in hardware ,version and platform.
Thanks

[snibgo]

Some action used to take "1 sec per page avg (max 2sec)". Now it takes "around 8 sec+".

Then something has changed. Software version, free space in memory, CPU availability, whatever. Something has changed.

[rishabh]

Yes we did rigorous check that if something has changed or not software is same. free space in memory has been increased,CPU is same...it terms of external dependency nothing has been changed. What could be the effects on change of code. If I decrease to DPI to 100 i see IM working fast but 300 DPI takes 10+ sec. What actions could lead to write operation slower ?

[fmw42]

What is your exact command line? What is your exact IM version and platform? IM 6.6.6 is ancient (at least 270 versions old). Perhaps you should upgrade. Does it happen with every PNG to TIF? Does it happen with other input or output formats? Have you tried a similar command line version of your conversion. Perhaps your code is faulty or corrupt? Has your versions of libpng or libtiff changed? Are they old and need to be upgraded? If you are just converting from PNG to TIF and setting the DPI, then DPI should have no effect, since you are not changing the number of pixels, only the meta data to be used to print the image.