What dpi setting is optimal for 35mm ?

[Mr Ho]

I am very new to scanning, and just picked up a cheap Epson 3490 Photo for office use that I will practice on before buying something a bit heartier. It offers 3200 dpi and 48 bit processing per the specs, but when I open up the Epson Scan program it seems I can set it to scan up to 13,200 dpi? I tried that setting and one 35mm negative frame came out after nearly 20 minutes at almost 100 MB !!

My questions are these:

1) What's the best dpi to set for scanning 35mm and have resolution to print up to 8x10 or 11x14?

2) Is there a website that adequately explains such dpi matters for novices like me?

Thanks in advance.

 

[Indrek]

My Epson 3190 produces 200MB tiff files :-D, 5 min. per frame
If you want to have usable prints, than that’s what you have to accept.
The resolution number depends on the size into witch you scan, if you set the settings to 10x15 cm. then the max reso will be 1200dpi.

 

[positivibes]

Dpi

Dpi

Forget whatever your Epson Scanner tells you about DPI. Ther's a big gap between DPI and "real DPI". You have to Scan a Test-Chart to see what resolution your Scanner can produce. For your Epson i guess it's about 2000dpi and lower. But to get this 2000dpi you still have to scan in the highest resoltion (in your case 3200dpi).

Good Filmscanners. like the ones fom Nikon, scan max. 4000dpi and about 3900 "real DPI". Only with one of these scanners you can trust the DPI Number in your Scan-Software.

About the best resolution: I scan my slides with 3000dpi. Thats aprox. the Resolution of a 12 MP camera. In my opinion 4000dpi is the max. you can get out of a slide (talking about a slide taken under best conditions with an expensiv film like provia). That is aprox. 23 Megapixel!

 

[willie_901]

It sounds like you are making all of your image adjustments (contrast, color cast,cropping) using the scanner and scanning to obtain a file for printing. In this case the DPI in you final file should be equal to the DPI of the printer device. It can be a bit larger (360 DPi instead of 300 for instance) because the printer software will downsize the DPI. This is much preferred to having the printer software upsize the DPI. In one case excess information is simple discarded (averaged actually) but in the other. the software algorithms have to create something out of nothing.

I would suggest a different workflow. Scan to make a digital negative that can be used for any purpose. The output dimensions (36mm X 24mm) of the scan will equal the negative size. Then you set the scan's PPI, not DPI. This approach is much more flexible and in principle you only have to scan once. Also post-processing software such as Photoshop, Lightroom and others is superior to scanner software for the same purpose.

For proofs I scan 35mm film at 1200 ppi and 16 bits (10.8 MB, 1.9 megapixels). This size scan is suitable for on-line viewing. Sometimes 2400 ppi scans (43MB, 5.4 megapixels) are useful too

For prints (8X10 or arger) I rescan at 4800 ppi/16 bits (~170 MB, ~30.6 megapixels).

I use .tiff files and scan B&W and color the same way.

The more you adjust a scan in post-processing, the more data you should collect. A 16 bit scan will suffer less from inevitable digital roundoff errors than an 8 bit image.

When you are done adjusting the image, you select the print size, the DPI appropriate for the printer and save/export the file as an 8 bit jpeg. I email my files to a local lab for printing. They want 300 DPI files. I sometimes send them 400-500 DPI files and trust the printer software to down size the DPI.

Shutterflower brings up an important point when he mentions that different negatives have different minimum requirements for scanning. That is, the less information in the negative, the less information you have to digitize to best represent the original. ISO 50 slide film is capable of recording more information than ISO 800 negative film. At the same time, a city scape on ISO 50 slide film on a perfectly clear day will have more information than a a seascape taken on a foggy morning using the same film and lens. The problem is, I am not aware of any software that evaluates the information content of an image. So, I collect the most information I can when I know an image will be printed at 8X10 or larger.

willie

 

[Pherdinand]

If you want to scan a frame for printing it later, scan at the 3200 dpi that is mentioned on the box. This is supposed to be the max optical resolution.
The larger dpi settings are interpolated. Photoshop can do the same from a 3200-dpi image, so no point in wasting lot of time and disk space above 3200 dpi.
Even 3200 is not really different than 2000 dpi, as said above. But there might be minor differences for very sharp and well exposed slow film frames.
So, just scan at 3200 dpi and then rescale the image in your image tweaking software to the size you want to print it.
E.g. 3200 dpi of a 35mm frame will result in approx. 3200 pixels along the SHORT size (24mm is almost an inch); dpi means dots per inch,. which translated to scanning dimensions should be pixels per inch in fact.
For the computer screen, the final dpi setting will NOT matter, only the size in pixels.
For printing, the DPI number will define the density of printing, i,.e. the resolution.
3200 pixels will allow printing about 10 inches on the short side (if you print at 300 dpi), that means a magnification of 10 x of the 35mm frame. Increasing the size will be possible since at prints larger than 10 " you can print at lower resolution, say 250 or even 200 dpi (since viewing distance will be larger).

The thing is, you could try a test scan of the best resolution film you have to see if there is a real 3200 dpi resolution; if not, scan at the highest valuable number and upscale it if necessary in photoshop.

 

[rxmd]

Forget whatever your Epson Scanner tells you about DPI. Ther's a big gap between DPI and "real DPI". You have to Scan a Test-Chart to see what resolution your Scanner can produce. For your Epson i guess it's about 2000dpi and lower. But to get this 2000dpi you still have to scan in the highest resoltion (in your case 3200dpi).

However, there is still an advantage to having a high nominal DPI value. Even a scanner with 4800 nominal and 1200 "real" DPI there is still a point to scanning at 4800 dpi and later downsampling to 1200 dpi (in 16bit mode). Effectively you're acquiring 16 data points for every pixel of your output image, just like multisampling. That means you get four extra bits of colour depth for free. To some this might be even more important than resolution.

Philipp