[jennverr]

i am so confused by all this information about scanning/printing, pixels and dpi, etc etc.

i do need to do some reading up on it. but here is what i am trying to figure out.

i shoot 120 film frequently, and would like to make large format prints out of them (specifically 13x13 at the least on my home printer, and possibly larger at some other point).

here is my question. I currently get them scanned at a place, high res is 3000x2000. When i get the neg back, I change the image size in pshop to whatever and make sure it's at 300dpi, and print it. but it still looks a little pixely to me.

is there any kind of chart somewhere that will show me if you scan your film at x resolution, you can get y size print??

or something similar to that?

somewhat related - does anyone use send out services for film processing/scanning, such as Dwaynes or thedarkroom.com??

OR, does anyone recommend a scanner that maybe it's worth purchasing my own for these purposes - but do home scanners get good enough resolution to do the large format prints?

thanks all! i hope this post makes sense, as i feel like i am not making much sense out of this stuff myself!

[Adam]

You should enter a width of 13 inches in photoshop. This should upsample your photo sufficiently for the print. Just changing the dpi will actually make the print smaller, as more pixels are needed to fill each square inch.

[stevebrot]

Adam's advice is good. Let the software do the work.


Steve

[Nesster]

You can work out the ratios yourself.

Consider that bitmap size of 3000x2000. Keeping this constant, and using your desired 300 DPI print resolution, divide the bitmap by 300:
10 x 6.6 inches

If you desire a 13" print = 300 x 13 = 3900 pixels long dimension. Your resized photoshop bitmap should be at least 3900 pixels wide - or if you are looking for a 13" square crop, then the shorter dimension needs to be that.

What resolution do you need to scan with, assuming a 2 1/4" negative, to get a 3900 pixel bitmap size?

3900/2.25 = 1733.3 dpi, or effectively you scan at 2400 dpi which gives you 5400 pixels in the bit map, which translates to 18" at 300 DPI, or more than sufficient.
the 2.25" negative at 1200 dpi scan = 2700 pixels or 9" printed at 300DPI

---

If you need to resize in Photoshop, you'll note that if you simply respecify DPI to 300 the bitmap doesn't change - but the 'print' dimensions do. This is why you need to specify a bicubic resize - enter the desired print dimensions and 300 DPI and the software calculates and resizes to your desired dimensions.

[jennverr]

Hi Nesster

Thanks, i've read your post over and over and it is sinking in. i don't know why i have such a hard time wrapping my head around this kind of stuff. math was def never my thing i guess! I will keep this formula in mind for the future.

[Nesster]

Perhaps you are a visual person? Think of DPI as how closely the dots or lines are to each other -- the closer the dots or lines the smaller the overall space taken, given the same number of dots or lines:

|||||||||||| = 12 lines close together, think 300 DPI
| | | | | | | | | | | | = 12 lines further apart, think 72dpi (actual scale would be 100DPI)


If you want the 300 to take the same space as the 72 DPI you have to triple the number of lines (via software, or in the days of using enlargers, the light expanded the lines):

||||||||||||||||||||||||||||||||||||

[jennverr]

Thanks again everyone. For anyone who may be interested, I found this very useful chart for the different sizes of film, ie what size scan you would need to print at 300 dpi. I have never heard of this company before, but might try scanning a few negs with them see how it goes!

120/220 Medium Format Negative & Transparency Scanning Prices at Pearson Imaging