tone mapping changes image size

[Dap Pan]

Hello everybody,

I'm using pfstools to tone map some hdr images in order to compare their original 0 exposure image with the tone mapped by finding PSNR and SSIM.
I just realized that the tone mapped images are not the same size as the original.
For example my original 0 exposure photo is 3900x2616 pixels and my tone mapped images are  3795x2547 pixels.

Could somebody explain me why is that happening?
Is there a way to avoid it?

Thanks a lot,

Daphne

[Rafal]

You need to post the full command line so that we can see how you tone-mapped the images.  

Tone-mapping does not change image resolution, but pfsalign may. 

Rafal