Converting tiff files to high res jpg files

[KmH]

Hi ,
I am new to printing learning.Learning though a lot through expert opinions. But i have 1 major questions which is confusing me
1) When I go for printing 4x6 photos , the vendor says his software wont accept TIFF. Actually he is lying and the only reason is that the files are big and slows down the printing process.But I dont want to give JPEG because it too small. How can I increase the resolution or PPI of the jpegs so they are not as large as TIFF but as good in picture quality as TIFF.

What brand and model of print making machine does your print vendor use?

What are the pixel dimensions (the resolution) of the photos you want to print? A human cannot see the difference between a print made froma TIFF file and a JPEG that was saved at a high quality setting.

Increasing the PPI just makes the final print smaller.

I am afraid you don't quite understand how all the numbers, like resolution and ppi, relate to file type and making prints.