Which DPI for creating digital negatives?

ChristopherCoy · Apr 19, 2020

I know that DPI stands for Dots Per Inch, and I know that the more dots you have the bigger your enlargement can be.

What confuses me is when product specs start mentioning other numbers like Mpx numbers, and #### x ####.

If my goal is to take 35mm negatives, scan them, and print them on transparency for platinum printing, is it necessary to pay hundreds of dollars for a scanner with 7200dpi?

I wouldn't see myself printing anything larger than 8x10, maybe an 11x14, and in perhaps once every three years or so occasions, a 16x20. And I know that some will scoff and say that 16x20's can't be printed from 35mm negatives, but they can, and I have, and I'm ok with them.

Bob Carnie · Apr 19, 2020

My printer is set at 300dpi for printing digital negs, it is ppi for others like when on my lambda which then runs at 400ppi
It is always best to start with the best file you can get for any printing, I have made very large murals from 35mm .

ChristopherCoy · Apr 19, 2020

Bob Carnie said:
My printer is set at 300dpi for printing digital negs, it is ppi for others like when on my lambda which then runs at 400ppi
It is always best to start with the best file you can get for any printing, I have made very large murals from 35mm .

Thanks Bob, I'm referring to the scanning of negatives though. If you're printing at 300dpi, do I need to waste money on a scanner that scans at 7200dpi?

Les Sarile · Apr 19, 2020

ChristopherCoy said:
I know that DPI stands for Dots Per Inch, and I know that the more dots you have the bigger your enlargement can be.

What confuses me is when product specs start mentioning other numbers like Mpx numbers, and #### x ####.

If my goal is to take 35mm negatives, scan them, and print them on transparency for platinum printing, is it necessary to pay hundreds of dollars for a scanner with 7200dpi?

I wouldn't see myself printing anything larger than 8x10, maybe an 11x14, and in perhaps once every three years or so occasions, a 16x20. And I know that some will scoff and say that 16x20's can't be printed from 35mm negatives, but they can, and I have, and I'm ok with them.

Not all represented "dots" mean the same thing.
For example, these are scans of the same frame of Kodak Ektar 100 using the Epson V500, V700 and Coolscan 5000 at their different settings - with and without ICE. Clearly at their highest optical resolution of 6400dpi, the Epsons doesn't even match the Coolscan at 4000dpi. The V500 doesn't improve above 2400dpi, the V700 makes small improvements up to 6400dpi while the Coolscan is much higher.

Full res -> http://www.fototime.com/89F76D805B0AFF8/orig.jpg

Full res -> http://www.fototime.com/C6858EE09C0BFDA/orig.jpg

Full res -> http://www.fototime.com/FB36D70B2409405/orig.jpg

Of course these are idealized - optimal shooting conditions, target with sufficient detail to show resolution, good quality film and on-screen evaluation. Printing at smaller sizes will definitely loose a lot of this detail. So, will the best scan resolution show up in your prints? You'll have to judge for yourself.

Adrian Bacon · Apr 19, 2020

Best results are usually had when you scan at the native sensor resolution of the scanner, then scale it down to a reasonable working/storage resolution. For 35mm negative, you’ll want to scan at least 2400 dpi/ppi if you plan to make a good sized enlargement.

MattKing · Apr 19, 2020

OK...
Scanners don't scan at dots per inch (dpi), they scan at pixels per inch (ppi).
Roughly speaking, if you want dots at the printing end, you need pixels at the scanning end, and the ratio is one pixel needed for each dot.
If your goal is to use a printer that makes 400 dots in every inch, to find the total number of dots needed, multiply the dpi by the number of inches.
For the simplicity of the example, lets say you wanted to make a print that is 12 inches by 18 inches. That means you need a digital negative that is 12 inches by 18 inches, made up with 4800 dots by 7200 dots (12x400 by 18x400).
In order to get that many dots from your printer, you need your digital file to have 4800 pixels by 7200 pixels. To get that many pixels from a negative that is 1 inch by 1.5 inches, your scanner needs to have a scanning resolution of 4800 ppi.
If your scanner has a scanning resolution of 7200 ppi, you could get the same resolution on a digital negative that is 18 inches by 27 inches.
If your scanner has a scanning resolution of 2400 ppi, you could get the same resolution on a digital negative that is 6 inches by 9 inches.
The true, optical resolution of most flatbed scanners maximizes out at about 2400 ppi. Anything more than that is actually done with software.

ChristopherCoy · Apr 19, 2020

Les Sarile said:
The true, optical resolution of most flatbed scanners maximizes out at about 2400 ppi. Anything more than that is actually done with software.

You are the big crayon master! THANK YOU!

MattKing · Apr 19, 2020

ChristopherCoy said:
You are the big crayon master! THANK YOU!

What - did Les steal that from me?!!!

Les Sarile · Apr 19, 2020

MattKing said:
What - did Les steal that from me?!!!

I think that's what is called the carbonero effect . . .

Adrian Bacon · Apr 20, 2020

MattKing said:
The true, optical resolution of most flatbed scanners maximizes out at about 2400 ppi. Anything more than that is actually done with software.

Depending on the scanner, that's not entirely true. The scanner may not have the optics to get much better than that, however that does not mean that there is software adding interpolating samples into the image if the sensor's native resolution is higher than 2400 dpi. Case in point, I have a Canon 9000FMkII (along with several other scanners, don't ask, it's a sickness) which has a sensor with a native 9600 dpi. The scanner does not get anywhere near that much resolution, but, when making a monochrome scan directly off the platen glass using the blue channel, it does resolve more detail at 9600 dpi than it does scanning at 2400 dpi. Enough more detail that when using it, I always scan at 9600 dpi then scale down later.

That being said, scanners do tend to advertise interpolated resolution and not actual native sensor resolution, so it is worth it to do some homework and find out what the native resolution of the sensor is.

jeffreyg · Apr 20, 2020

As mentioned scan at the maximum your equipment can produce and scale down in increments to a reasonable file size. To me content is more important in the end.

http://www.jeffreyglasser.com/

sculptureandphotography.com/

ChristopherCoy · Apr 20, 2020

I just picked up an epson V330 for $79 with free shipping. It's in the box with all accessories. Resolution is 4800x9600 which if I'm understanding the Crayon Master's explanation correctly, would be sufficient for up to an 11x14 digital negative enlargement at 400dpi.

brbo · Apr 22, 2020

ChristopherCoy said:
I just picked up an epson V330 for $79 with free shipping. It's in the box with all accessories. Resolution is 4800x9600 which if I'm understanding the Crayon Master's explanation correctly, would be sufficient for up to an 11x14 digital negative enlargement at 400dpi.

No, V330 is probably closer to 1500dpi (true resolution). 4800dpi is sensor resolution and 9600 is probably stepper motor resolution. But since the lens can't resolve more that 1500dpi... 1500dpi is what you get.

ChristopherCoy · Apr 22, 2020

brbo said:
No, V330 is probably closer to 1500dpi (true resolution). 4800dpi is sensor resolution and 9600 is probably stepper motor resolution. But since the lens can't resolve more that 1500dpi... 1500dpi is what you get.

Unless you can explain your claim, I'm going with what the factory says.

Optical Resolution
4800 dpi x 9600 dpi
Interpolated Resolution
12800 dpi x 12800 dpi
Type
flatbed scanner
Interface Type
USB 2.0
Form Factor
desktop
Input Type
color
Scan Element Type
CCD
Document Size Class
A4/Letter
Max Supported Document Size
8.5 in x 11.7 in
Max H-Document Size
8.5 m
Max V-Document Size
11.7 m
Grayscale Depth
16-bit (64K gray levels)
Grayscale Depth (External)
16-bit (64K gray levels)
Color Depth
48-bit color
Color Depth (External)
48-bit color
Max H-Optical Resolution
4800 dpi
Max V-Optical Resolution
9600 dpi
Max H-Interpolated Resolution
12800 dpi
Max V-Interpolated Resolution
12800 dpi
Lamp / Light Source Type
LED
Supported Document Type
film, plain paper, transparencies
Document Feeder Type
manual
Scanner Features
EPSON ReadyScan LED Technology

bernard_L · Apr 22, 2020

ChristopherCoy said:
Unless you can explain your claim, I'm going with what the factory says.

Optical Resolution
4800 dpi x 9600 dpi

Interpolated Resolution
12800 dpi x 12800 dpi

What they call "Optical resolution" is actually "Sampling Resolution", i.e. how finely sampled are the pixels in the (linear) array and how finely the stepper motor advances(§1). How sharp is the image delivered by the image-forming optics is another matter, generally worse(§2); it is this latter number that Adrian Bacon and brbo are referring to. The "Interpolated resolution" is a further step into disingenuous marketing (to speak politely). Admittedly, I'm just repeating what previous responders wrote, but worded differently, maybe the message will get through?

(§1) Actually more complicated; as concerns the V700, it has a staggered pattern of pixels, plus the firmware does things before pixels are delivered over the USB cable; this does not change anything fundamental in my statements above.
(§2) In technical terms, the optical image is oversampled. Meaning the sampling frequency is more than twice the spatial frequency at which the MTF drops to zero. That is not bad per se, and a.o. guarantees that no information present in the optical image is lost. Mind you, none is created either. Because of that oversampling, I have serious doubts that grain aliasing is ever a real concern, despite being frequently mentioned in forums.

brbo · Apr 22, 2020

ChristopherCoy said:
Unless you can explain your claim, I'm going with what the factory says.

I already explained why the true resolution is around 1500dpi. Find a test of a consumer Epson/Canon flatbed and you'll soon realise that 4800dpi is a dream. 2500dpi for V800/V700 is pretty much the best you can hope for. 1500dpi for V330/V500/V600. I have a range of scanners (from flatbed to drum scanner) and have tested them so I'm not making this up.

Maybe this review will help you to "not go with what the factory says"?

ChristopherCoy · Apr 22, 2020

Great. So I spent $80 on a crap scanner. I knew I should have saved my money and just sent film to a lab.

Because when you say that 1500dpi "is what I get", I hear "you've wasted your money."

Mainecoonmaniac · Apr 22, 2020

Sending a file to a printer that exceeds it's native resolution does not improve quality improve image quality. On my Canon Pro 100, a minimum resolution of 200 dpi will work. I've been able to use 200-300 dpi for my digital negs. Printing at higher dpi just chokes the computer and slows down the process. Another thing to consider is how much the ink will spread on a particular print material also called dot gain. With OHP film, dot gain will be lower than paper so a higher dpi might work but not necessarily improve the image quality. But I would experiment. Start with an image that's 100 dpi and work your way up to 400 dpi. Make prints with the neg and look at it under a loupe. You'll probably find you'll need a lower dpi than you think.

bernard_L · Apr 22, 2020

ChristopherCoy said:
Because when you say that 1500dpi "is what I get", I hear "you've wasted your money."

Rephrasing part of the other guy's post in an offensive way is one tried-and-true method to send the thread in a spin.

This said, with 1500dpi real resolution, all is not lost. Assume 200dpi target resolution for the print (see above post). Room for 7.5x from negative. 18x27cm print, not so small. Besides, larger prints are not meant to be looked at from the same distance as wallet-sized prints.

Important. 1500dpi is the resolution at which the contrast drops to zero. You'll want to restore the MTF at the high frequencies. Use USM sharpening. Typ sigma 1 to 1.5 pixel. Stop increasing the intensity (or %, whatever) of sharpening when line halos appear and back off the intensity until they disappear; overcooked sharpening is ugly; proper sharpening is effective.

MattKing · Apr 22, 2020

ChristopherCoy said:
Because when you say that 1500dpi "is what I get", I hear "you've wasted your money."

As others have posted, it isn't that bad!
If you intended to convert your scans into a whole bunch of 20"x30" colour lambda prints, you would definitely see better results from a scanner that cost ten to thirty times as much.
You do, however, have three things going for you:
1) much of what you will want to do with your scans will be much less demanding. Smaller prints, or sharing images through the internet (such as on Photrio) are much less demanding, and require much less resolution;
2) as bernard_L posts above, scanned digital files need digital work, but digital work definitely improves scanned digital files. Once you learn a bit, the digital sharpening (in particular) tools become easy and quick to use; and
3) you earlier expressed an interest in making digital negatives in order to prepare contact prints using traditional and alternative processes. Many (most?) of those traditional and alternative processes offer less resolution than "normal" darkroom prints. So your lower resolution files may be just fine for your purposes.
Regarding point #1 - the following image as posted here is just 850 x 635 pixels - it has been resized down tremendously from the original much higher resolution 5400 x 3600 pixel scan (from a 6x4.5 negative) from which I have had made some very nice 12" x 16" RA4 colour prints.

Adrian Bacon · Apr 22, 2020

bernard_L said:
What they call "Optical resolution" is actually "Sampling Resolution", i.e. how finely sampled are the pixels in the (linear) array and how finely the stepper motor advances(§1). How sharp is the image delivered by the image-forming optics is another matter, generally worse(§2); it is this latter number that Adrian Bacon and brbo are referring to. The "Interpolated resolution" is a further step into disingenuous marketing (to speak politely). Admittedly, I'm just repeating what previous responders wrote, but worded differently, maybe the message will get through?

(§1) Actually more complicated; as concerns the V700, it has a staggered pattern of pixels, plus the firmware does things before pixels are delivered over the USB cable; this does not change anything fundamental in my statements above.
(§2) In technical terms, the optical image is oversampled. Meaning the sampling frequency is more than twice the spatial frequency at which the MTF drops to zero. That is not bad per se, and a.o. guarantees that no information present in the optical image is lost. Mind you, none is created either. Because of that oversampling, I have serious doubts that grain aliasing is ever a real concern, despite being frequently mentioned in forums.

+1

ChristopherCoy · Apr 22, 2020

MattKing said:
A
1) much of what you will want to do with your scans will be much less demanding. Smaller prints, or sharing images through the internet (such as on Photrio) are much less demanding, and require much less resolution;

3) you earlier expressed an interest in making digital negatives in order to prepare contact prints using traditional and alternative processes. Many (most?) of those traditional and alternative processes offer less resolution than "normal" darkroom prints. So your lower resolution files may be just fine for your purposes.

THIS. This is all I need to know at this point. Throwing a bunch of numbers at me about something I don't understand already just makes me feel like I wasted my money. If the V330 that I purchased can give me enough resolution to make an 8x10 digital negative, and allow me to test the waters with alternative processes, that's all I need.

Adrian Bacon · Apr 22, 2020

MattKing said:
As others have posted, it isn't that bad!
If you intended to convert your scans into a whole bunch of 20"x30" colour lambda prints, you would definitely see better results from a scanner that cost ten to thirty times as much.
You do, however, have three things going for you:
1) much of what you will want to do with your scans will be much less demanding. Smaller prints, or sharing images through the internet (such as on Photrio) are much less demanding, and require much less resolution;
2) as bernard_L posts above, scanned digital files need digital work, but digital work definitely improves scanned digital files. Once you learn a bit, the digital sharpening (in particular) tools become easy and quick to use; and
3) you earlier expressed an interest in making digital negatives in order to prepare contact prints using traditional and alternative processes. Many (most?) of those traditional and alternative processes offer less resolution than "normal" darkroom prints. So your lower resolution files may be just fine for your purposes.
Regarding point #1 - the following image as posted here is just 850 x 635 pixels - it has been resized down tremendously from the original much higher resolution 5400 x 3600 pixel scan (from a 6x4.5 negative) from which I have had made some very nice 12" x 16" RA4 colour prints.View attachment 244486

+1

Adrian Bacon · Apr 22, 2020

ChristopherCoy said:
THIS. This is all I need to know at this point. Throwing a bunch of numbers at me about something I don't understand already just makes me feel like I wasted my money. If the V330 that I purchased can give me enough resolution to make an 8x10 digital negative, and allow me to test the waters with alternative processes, that's all I need.

at the risk of me being pedantic, it would probably help you tremendously to spend a little time gaining some understanding of what those numbers mean. More knowledge is rarely a bad thing, and there are people on here that are willing to help you gain that knowledge if you ask questions.

MattKing · Apr 22, 2020

My suggestion would be that you first choose a known good 35mm original negative and then scan it at a number of different resolutions - 1600 ppi, 2400 ppi, 3600 ppi, 4800 ppi would be good choices.
Next, after storing those original scans in an appropriate folder - I often call mine "original scans" and label the files with filenames that incorporate the scanning resolution (e.g. 2020-04-22-18-2400 for frame 18 scanned at 2400 from the roll shot on April 22, 2020).
Next, practice using the sharpening and re-sizing tools available to you. For an 8x10 digital negative your final target will most likely be a 2400 x 3000 pixel file (assuming a 300 dpi printer). Your eventual goal will be to get a result that works well with the process you intend to use, but in the meantime you should aim for a result that looks good when in positive form.
Once you have practiced a bit, you will start to get a sense of where the sweet spot is for your scanner - it might come from the 2400 ppi scans, or maybe from the a different resolution.
Scanning and dealing with scanned files is a skill in itself! It is worth reading up on.
You will also soon gain practice in dealing with dust - particularly with 35mm black and white!

Which DPI for creating digital negatives?

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