Scanning help please

[Lynda]

I scanned some pictures at 300 dpi and some at 600 dpi, saved as tif files; then opened with the photo editor and saved as jpg files. But the jpg files are only 250 dpi. What is happening ... can anyone explain this?

So then I thought if I scan directly to jpg at 600 dpi, problem would be solved. But no, they are still 250 dpi.

I would really like to have the jpg files at a higher dpi, because I need help with restoration.

Any suggestions?

Oh jeez, I just realized it is 4 a.m. here on the Canadian prairies, and I have to get some sleep. Will check back in later.

[Anne in Carlisle]

Jpeg files seem to be strange things! We can't really get our heads round them either. However one tip - if you have to re-save a jpeg file find the 'jpeg options' somehwere in your photo handling program. Make sure the pointer is set right up to 'save at 100% of original'. I think sometimes they are reduced in size by default.

Bizarrly - sometimes when I save a jpeg file it is twice as BIG as it was

Anne

[Lynda]

Thanks for the reply Anne.

The photo editing program that I use is PhotoStudio ... a cheapie that came with my camera. Can't find anywhere in it to specify jpg options. What I did finally happen across with my scanner is that if I specify to save a jpg file to greyscale at 600 dpi, it does exactly that. And since most of the pictures I am currently working with are black and white, it's a sort of solution.

I found the same thing with the resizing that you did ... that if you save a 600 dpi tif file to jpg the result is at lower dpi, but much larger in dimension. Wierd! At work (before I retired) we attributed such things to gremlins.

Thanks again.

Lynda

[Guy]

The answer to this is in the way scanners printers etc measure resolution.

Scanners and cameras use Samples per Inch (SPI), the more samples per in the higher the resolution.
Printers (inkjet & laser) use Dots per Inch (DPI) or (thermal transfer) Lines per Inch (LPI)
Monitors and screens use Pixels per Inch (PPI)

These though similar are not the same.
Some manufactures simply use DPI to avoid confusing the customers, but this leads to confusion in use.
Cheers
Guy

PS
I should really have put-
Some manufactures claim to use DPI to avoid confusing the customers, when really their products use SPI, but this leads to confusion in use.

[Lynda]

Thanks for the explanation, Guy. I'd like to say I understand, but I'm just confused. That's ok, it's my normal state.

Lynda