Saturday, November 17, 2007

The Resolution of Digitized Negatives

Companies that digitize negatives provide a variety of resolutions at a range of prices. Which means you have to decide which resolution fills your particular needs. The three most popular resolutions for negatives appear to be 2000 dpi, 3000 dpi, and 4000 dpi. Not all firms provide scanning services at all resolutions, and if you have hundreds of rolls to do then the increased prices for higher resolutions will have an impact on your budget. So what does each resolution get you?

Let's do a quick review. Remember that resolution is measured as pixels per inch which is the same as dots per inch or dpi. Resolution is also relative. You can't really talk about resolution without also considering the medium on which the image appears. For our purposes there are two resolution that we need to worry about: the resolution at which the negative is scanned and the resolution of any reprints we want to make from that image.

A 35mm frame is 24mm x 36mm (or it's supposed to be anyway). So a 2000 dpi scan should result in an image that is 1890 x 2835 pixels. Most labs that make prints from digital images will tell you that a print will only look good if its resolution is least 200 dpi, and many recommend at least 300 dpi. If this image (1890 x 2835) is printed at 4 x 6 inches the result would be about 472 dpi, which is great. At 8 x 10 inches it would be about 236 dpi, or marginally acceptable.

Here is a list that compares the three common scanning resolutions and what enlargements they are able to support:
  • 2000 dpi: 1890 x 2835, good to 5 x 7, marginal to 8 x 10
  • 3000 dpi: 2835 x 4252, good to 8 x 10, marginal to 11 x 17
  • 4000 dpi: 3780 x 5669, good to 11 x 17, marginal to 16 x 20
So the choice of resolution depends on what you want to do with the results. If you want to make good looking enlargements up to 8 x 10 then you should consider scanning at 3000 dpi. If you plan on going larger than that you need 4000 dpi. But most people will not print larger than 4 x 6 except on rare occasion. For that purpose 2000 dpi is adequate.

If you understood all that then you need not read any further. If you're still scratching your head then let me try to clear the confusion. Remember that resolution is a relative measure. It depends on the size of the physical medium. The size of a jpeg image is always best expressed as actual pixels just for this reason. Imagine you have a jpeg that is 1500 pixels wide by 1200 pixels high. If you print this image at a size of 5 inches by 4 inches it will be printed at a resolution of 300 pixels per inch (dpi). That's because 1500 pixels divided by 5 inches is 300. Now if you take that same image and print it at a size of 10 inches by 8 inches, the resulting resolution will only be 150 dpi (1500 divided by 10). The same image printd at different sizes yields different resolutions.

Now let's go back to the negatives. When a negative is scanned the equipment picks up information at a predefined density, or resolution. If a negative is scanned at 2000 dpi, that means it measures levels of light and color at 2000 different, equally spaced, distinct points for every inch of the frame. A frame is supposed to be 24mm high by 36 mm wide, although some cameras might not get that exactly correct. Convert those millimeters to inches and then multiply by the density and you get 1890 pixels high and 2835 pixels wide. Once that scan is made and converted in to a jpeg, you cannot add information to it. Sure you can make it larger but you would have to extrapolate (or in other words "guess") the extra data. So for all practical purposes that image is 1890 x 2835 and no larger. Take that image and put it on a sheet that is 4 inches by 6 inches and it will be at a resolution of 472. You can get this number using simple math: 1890 pixels divided by 4 inches (or 2835 pixels divided by 6 inches). Well, actually its 472.5, but I rounded down.

It gets a little more interesting when you print that same image on a 5 x 7. The reason is that the frame doesn't quite fit on a 5 x 7. If you let the 2835 horizontal pixels exactly fill the 7 inches, then the 1890 vertical pixels will only cover 4.6 inches and you will end up with ugly white stripes at the top and bottom of the print. So the image has to be cropped on the sides to make the vertical pixels fit. The highest resolution you can achieve, then, is 1890 divided by 5, or 378. Got the hang of that now?

When I start scanning my collection of negatives I will probably stick with 2000 dpi. First, I need to hold the costs down. Second, nearly any reprints I will want will be 4 x 6. I am also planning on keeping my negatives, so on the rare occasion when I feel I want an 8 x 10 or larger I can always go back to the original negative and have it printed from the source.

Monday, November 12, 2007

Review: Imagers

Using Imagers for my negative scanning appealed to me for two reasons. First they are the only place I can find that digitize the frames at 4 different resolutions. Second, they are based in the Atlanta area which would eliminate shipping charges for me. I selected two representative rolls from my collection and dropped then off at the Imagers office in Atlanta at around 5 pm on a Monday. Each roll was stored in its own PrintFile negative archival page. By Tuesday afternoon they called me to tell me that my job was done and I could pick it up anytime. Their web site says a typical turnaround is 3 days, but they got mine done in a day! The package included my negatives in the archival pages (just like I had left them) and a jewel case with my disk and two "insert-sized" pages of thumbnails.

The negatives were mine and the thumbnails were my photos. Unfortunately the images on the disk were not mine. Even though the job number written on the disk was correct, somehow my order had been replaced with someone else's. I called Imagers the next day and they were very apologetic. They promised to put the correct images on a disk and ship it to me overnight. The following afternoon my disk arrived via UPS at no additional cost to me, and this time it contained the correct images.

Imagers is one of the most expensive labs I have seen, but they digitize every frame at 4 different resolutions. The idea being that you can choose the resolution you need for the application you have. Small images are intended for use on the web and as mail attachments. Intermediate sizes can be used for reproducing 4x5 photos, and the largest size is big enough to print 8x10 photos. The disk I got back had the following imae sizes:
  • Extra large: 4050 x 2712 (2800 dpi)
  • Large: 3150 x 2109 (2222 dpi)
  • Medium: 1805 x 1209 (1300 dpi)
  • Small: 500 x 335 (360 dpi)
The medium is large enough to create a 4x5 image and still have 300 dpi. The large is enough to print at 8x10 and have over 300 dpi. The extra large should be quite adequate for nearly any possible need, but I find it odd that it isn't 3000 dpi like many other companies provide. But what disappoints me most is the small is actually too small. These days screens don't get much smaller than 1024x768 and many of them have an even higher resolution. When I place my photos on a web site I typically make them 800 x 531 and would never make them smaller than 600 in their widest dimension. So an image of 500 x 335 seems too small, and is certainly a size that I don't have much use for.

The other disappointment with the results is the complete lack of organization for the images on the disk. I asked Imagers if they would organize the images by roll, and they said they were unable to do that. So my two rolls of pictures appeared on the disk in a single directory with sequential numbers from 1 to 46. The first roll was 1-25 and the second roll started after that. Even more frustrating was the fact that the numbering did not match the order on the negatives. Each strip was digitized and the images were numbered in reverse. So as I step through the images on the disk in numerical order, I am actually looking at frames 4, 3, 2, 1, then 8, 7, 6, 5, and so on. In order to get the files back in a coherent order I had to do some Unix shell scripting to get the file names in to a sequence that matched what was on the original negative strips.

On the plus side, all images were remarkably free of dust and other speckles. They were all framed and oriented correctly. Most of the images were color balanced correctly, although some outdoor shots were not. I was pleased with the resulting images, and the negatives made the round trip unharmed.

The bottom line with Imagers is that the extra resolutions they provide are outweighed by the inconvenience posed by the poorly organized file structure, and for me the higher price cannot be justified. Here is a sample image from the set I sent in for processing.


fast turnaround and good quality results
excellent service
despite 4 resolutions, none suitable for web
cannot separate rolls
files are not numbered in same order as negatives

Comparing Prices for Digitized Negatives

I have been comparing prices from a variety of places which digitize 35mm negatives to see who has good deals. In addition to the price per frame, most places charge for shipping and some places have additional charges for disks or other hidden fees. So creating a price that is truly comparative was a bit of a challenge. It is also complicated by the fact that not all vendors digitize at the same resolutions. Many vendors will digitize at 2000 dpi or 4000 dpi, and some also provide 3000 dpi.

The chart below presents prices for each of the vendors based on the estimated cost to digitize a 25-exposure roll of 35mm color film. I chose 25 exposures because most people who use 24-exposure rolls are usually able to squeeze one or two extra frames on the end. I arrived at this estimate by calculating the total cost for scanning 300 frames, including any additional fees for disks and return shipping. Then this number was divided by 12. This estimate allows for consolidation of multiple rolls on a single DVD as well as amortizing the cost of shipping across a larger order. If there was no information on the cost of return shipping I estimated it to be $10. I have also included approximate turnaround times. Note that none of these prices includes the cost of shipping materials to the vendor.

Estimated price to digitize a 25-frame roll of color 35mm film:

White Glove711.0217.27
Image Preserve1017.0821.2524.58

Notes: Imagers includes 4 scans per image: at 2800, 2222, 1300, and 360. ScanCafe ships material to India for processing. BritePix ships its material to Costa Rica for processing. Both PixMonix and DigMyPix provide web-based post-scan approval before cutting the disk.

Friday, November 9, 2007

Digitizing Negatives

One of the problems that I have been trying to solve lately is what to do with my rather sizable collection of negatives. I won't call it "large" but it is big enough that I need to get everything sorted, labeled, and archived somehow. My wife is also anxious to throw away boxes of old prints that we will almost certainly never use.

In this digital age the obvious choice is to digitize all the negatives. This preserves them and makes generating backup copies easy. My first attempt at tackling this was to purchase a MicroTek 4000tf negative scanner. I used it to digitize around 30 rolls from the 90's. But it has its drawbacks. First, I cannot adequately control the dust in my office environment, so the resultant scans would not be adequate for making prints and certainly not for making enlargements (should I ever choose to do such things). Second, the process takes time. A roll of 24 exposures typically takes about an hour. And this isn't "set it all up and go away for an hour", this is an hour that requires action every 5 minutes. So it is time consuming and labor intensive. I'm also not entirely satisfied with the 4000tf. Since it only has one gear to move the negative cartridge, the cartridge does not always stay aligned correctly and as a result the scans tend to be slightly crooked. It's hard to notice after cropping, but in order to crop away the crookedness I end up losing more of the frame than I would like.

Recently a friend suggested I try one of the many digitizing services. I initially dismissed them as too expensive but on second glance I think the savings in time and the better quality may be enough to justify the expense (and some of them are priced reasonably). So as I experiment with each of these labs I intend to post the results here to benefit anyone else that may stumble across this blog.

So far I have found the following labs that advertise they will digitize strips of 35mm negatives:
  • Imagers
  • ScanCafe
  • BritePix
  • Image Preserve
  • PixMonix
  • Larsen
  • DigMyPix
  • White Glove
Prices vary widely but generally range from $11 to $24 for a roll of 25 digitized at either 2000 or 3000 dpi. The big exception is ScanCafe which charges an amazing 19 cents per frame for 3000 dpi, what works out to about $5 per roll. Why are they so cheap? Well the 36-day turnaround ought to give you a hint: they send everything to India for digitizing and processing.

When I have time I will post a price comparison of the shops I've found, and I will try to take in to account all the hidden costs (such as disks and shipping).