Can someone explain me about the drum scan ppi?

[rustyair]

I've been trying to understand about the ppi and MB regarding drum scan. As you can see below, if I want to make a 40x50 print from a 4x5" film, there are 3 options,

PMT Drum scanning

40x50
200ppi 228mb / $125
300ppi 515 mb / $275
400ppi 915mb / $475

Does that mean '400ppi 915mb / $475' print will look much sharper than 200ppi and 300ppi? or maybe 200ppi sharp enough?

There's a huge price difference between these. Can someone explain me about this?

Thanks,

[bob carnie]

400 ppi is most likely for lambda printing, you will see a difference in small type over 200 ppi on the same unit. It is slight difference and for general printmaking not worth the difference.
A larger file size will allow you to print larger if that is your goal.
For our silver gelatin prints off the lambda we do have to print at 400ppi.

[Lenny Eiger]

I've been trying to understand about the ppi and MB regarding drum scan. As you can see below, if I want to make a 40x50 print from a 4x5" film, there are 3 options,

PMT Drum scanning

40x50
200ppi 228mb / $125
300ppi 515 mb / $275
400ppi 915mb / $475

Does that mean '400ppi 915mb / $475' print will look much sharper than 200ppi and 300ppi? or maybe 200ppi sharp enough?

There's a huge price difference between these. Can someone explain me about this?

Thanks,

These prices are very expensive. I do a 4x5 at what I consider to be full rez, 4000 ppi, for $135 (vs their $875). This translates to 1.75 gigs. Your 50 inch print would be at 400 dpi at. This is good, since 360 is even better (ever so slightly) you might crop a little off the edges, etc. I can also do a 8000 ppi scan, which results in a 6 Gig file, for very large prints, and since it takes a very long time, I usually double the cost. However, its still lower than their 400 dpi rate.

The math is easy, if you get all the numbers. The number of megabytes is the most useless figure. The ppi/spi/dpi of the scan on a drum scan gets multiplied by the inches. Thus, a 4000 ppi/spi/dpi scan of a 4x5 yields 20,000 pixels along the long edge. You can then divide this number by your printing resolution to get the max print size at top quality, or you can divide it by the number of inches to get the resulting resolution.

Sometimes the numbers on a ccd scan, whether it be a flatbed or Imacon or film scanner, are the total number of pixels along that edge, so they would get divided by the inches. It depends who you are talking to.

The best number is the total number of pixels along the longest edge. You can then divide this number to get the info you need...

Hope this helps.

Lenny

[rustyair]

Thanks all!

[John Rodriguez]

I corresponded with Charles Cramer on the subject of optimal PPI, and he revealed that through testing he and Joe Holmes had settled on 2200 PPI for their work. Higher res scans gave them little improvement.

[Lenny Eiger]

I corresponded with Charles Cramer on the subject of optimal PPI, and he revealed that through testing he and Joe Holmes had settled on 2200 PPI for their work. Higher res scans gave them little improvement.

I know both Joe and Charles and have corresponded with both of them as well, on different issues. These results may very well be hardware dependent. They use a Tango. They have their own working methods. I have seen lots of improvement over the 2000 to the 4000 and the 8000.

Everyone has their way of working, and different ideas about what they are after in a print, etc. Charlie is very good at getting what he wants out of his machine. However, his numbers are specific to his situation.

A 10 micron aperture is easily attainable on my scanner for Delta, for example. That would suggest that 4000 ppi is at least a minimal mark. I believe there is even more at the 8,000 level. In the one test we did together years ago, Charlie was very frustrated that my scanner resolved more bars. What does it mean? Who knows? There's a million variables. However, if you ask me, those numbers are quite low.

Lenny

[Richard Kenward]

Dear Lenny

I've not dipped into this forum for some time and have just spotted this thread. Just a few thoughts. IMO at the end of the day much depends on the quality a particular scanner can produce, the condition it is in, the software and perhaps the most important element which of course is the person making the scans. It is also worth saying that running a drum scanner is not cheap especially if it is professionally maintained. Making the best scans takes time, often lots of it and dedication, all of which has to be charged for if the business is to flourish. Like you I'm not interested in a business model of producing scans at low rates, and would far rather spend my time working with demanding clients who recognise that a professional set-up with top quality equipment and the necessary skills cannot be had for peanuts.

Cheers Richard Kenward (precision-drum-scanning.co.uk)

[Nathan Potter]

Lenny, I'm a relative dunce about drum scanning so if I may, I'll ask a couple of questions that have been bugging me in reference to the scanner you use.

When you talk about a 10 µm aperture or other size is that the size of the scanning spot on the emulsion? What is the uniformity of illumination within the scanning spot?

Are the RGB channels separate scans (separate scanning apertures) done at the same time or RGB multiplexed channels utilizing the same aperture?

Nate Potter, Austin TX

[Lenny Eiger]

When you talk about a 10 µm aperture or other size is that the size of the scanning spot on the emulsion? What is the uniformity of illumination within the scanning spot?

Let me see if I can clear this up...

The drum rotates around and the sensor takes a number of samples around the circumference. This is the spi (samples per inch), very close to the ppi, for all practical intents. Then the drum (or the sensor) moves over and it does it again and again across the whole image.

The aperture is the width of the sample. If it matches the size of the grain, everything is sharp. If it is too small, there is a grainy effect that occurs (anti-aliasing) that is not grain but looks a little like it. If the sample size is too wide then the scan is blurry.

The illumination is constant.


Are the RGB channels separate scans (separate scanning apertures) done at the same time or RGB multiplexed channels utilizing the same aperture?


In my scanner there are three PMT's, one for each channel. Light is brought in to the dark chamber thru a rotating disk with different size holes in it (for the sample sizes) and a mirror. Inside there is a splitting mirror that separates the R, G and B light and directs it to the correct PMT. One sample width is therefor used for all the channels.

I hope that answers it.

Lenny