The two most common questions I get about scanning photographs are:
1) What DPI do I need to scan my photo?
2) What file format should I save the file in?
DPI stands for dots-per-inch, and refers to how many pixels are present in each inch of the photograph. For example, if you had an 8×10 inch photograph, and you scanned it at 100dpi, you would have a photo that was 800×1000 pixels, or 800,000 pixels altogether. That’s less than a million pixels, or another to say it is it is less than a megapixel. Doubling the DPI to 200dpi, gives you 1600×2000 pixels, or 3,200,000 pixels, or 3.2 megapixels. Note that doubling the DPI effectively quadruples the number of pixels, since the dpi increases in both vertical and horizontal directions.
Here’s another way to look at, in a slide from my presentation:
Basically, if you look at scanning photographs (or negatives/slides) you can see that scanning it at 300dpi for different sizes will give you much different size images. I have a rule-of-thumb that I use to determine the correct DPI to scan at, and basically it has to do with figuring out the largest size you want to be able to print (printing is usually done at 300dpi) and then adjust your scanning dpi to insure you’ll have enough pixels to print. Here’s the summary:
For people reading this on a small screen where the image is hard to read, the basic rule is:
Minimum resolution (DPI) should be the number of inches of the largest side you want to print, divided by the largest side in inches of what you’re scanning, multiplied by 300.
So if you are scanning a 4×5 print, and want to be able to print at 8×10, you need twice the DPI you’ll print at, so 600dpi. Of course, it doesn’t hurt to scan more than you need, although there are diminishing returns. Not all photographs are high enough quality to give you a better picture when scanned at very high resolution.
A Kodachrome slide supposedly has enough resolution to output about 20 megapixels. That means you can basically max out a 4000dpi slide scanner and get a good result. That said, a small old print with lots of grain probably wouldn’t benefit by going beyond my rule of thumb, and some likely could be safely scanned at a lower resolution.
Storage is cheap though, so I say scan as high a resolution as you want, and use my rule of thumb as the minimum guideline.
So once you’ve figured out what resolution to scan in, what format should you save it in?
The short answer is TIFF. TIFF was actually designed early on for the purpose of scanning photographs. TIFF also, for the most part, does not lose any data in the file format, unlike formats like JPEG which always compress data in a lossy fashion (I say for the most part because it’s technically possible to use JPEG compression in a TIFF file, but it’s rare, and I doubt any scanner software you would use is going to do that). You can scan to TIFF format using LZW compression that is lossless (i.e. does not degrade the photo quality). TIFF is also good because it is so widely supported, and is used by archives and libraries for their own scanning, and is unlikely to become unsupported by future software.
PNG is also a good format for scanning. It’s a more modern format, and offers built-in lossless compression. It’s not as widely supported, but if space is at a premium, it might save you a bit over TIFF.
JPEG is not a good format for scanning, because it a lossy compression format, and you will always lose some data when saving to a JPEG, even if you save it at 100% quality. I sometimes scan to both TIFF and JPEG, as JPEG can be easier to share sometimes, but I am sure to have the TIFF file as well.
PDF is not a good format to scan photographs with, as you have no control over how images are compressed, and editing them is much more difficult than TIFF or PNG. In general, PDF files will actually use JPEG compression anyways, without being able to even set the quality. If you’re scanning a multi-page printed document, you can use PDF as a convenient way of sharing it, but if there are photos and other important content in the document, I would suggest scanning it as a TIFF as well. It’s not well known, but TIFF also supports multi-page documents, just like PDF.
If you have additional questions about scanning photographs, please post them in the comments below.
As the cameras built-in to cell phones get better and better (and indeed every year the improvement has been significant), more and more people are using their phones instead of dedicated scanners for duplicating documents and photographs.There are many iPhone apps for scanning documents, such as CamScanner Pro, Doc Scan Pro, Genius Scan+, JetScanner, Prizmo, Scanner Pro, TurboScan, and the genealogy-focused Shoebox (now owned by Ancestry.com).
Android also has their share of apps, like CamScanner, Document Scanner, Droid Scan Pro PDF, Handy Scanner Pro, Mobile Doc Scanner, and there’s also an Android version of Shoebox.
Other popular apps like Evernote are also suitable for this kind of document and photo scanning.
|Perspective correction in Genius Scan+|
Most if not all of these apps do something pretty neat, which is that they will take your document or photo and if the corners are not 90 degrees, it will correct the perspective. This is necessary because most people holding a camera in their hand cannot possibly get the camera lens to be perfectly parallel to the document or photo they are photographing. This causes the photo they take to be skewed (where for example one side of the photo is smaller than the other side), and thus the need for this correction technology.
The problem with this technology is that you can never correct something like this without losing some quality. Wouldn’t it be better if you could insure your phone was parallel to the document when you take the photograph? When people traditionally took photographs of documents, they used big bulky copy stands. They are generally bulky and expensive. So what solution exists for your cell phone? Turns out this is a problem several people have taken a look at, and there are some very interesting solutions.
Let’s start out with free. Designer Kyle Koch has designed a cardboard stand he calls the iPhone Document Scanner, which he provides the plans for in EPS format. You can print out the designs and cut these out using cardboard or other materials yourself.
If you want to order it pre-made, it’s also available from Ponoko in either corrugated cardboard or MDF. A newer version, called the ScanDock (maybe soon to be ScanDeck as there is another ScanDock – see below), is available only in cardboard, and the plans are not available for free. Oddly, the different products all have different and bizarre shipping options. The best option seems to be the ScanDock which costs $25 and can be shipped to the contiguous US for $8.50. If you’re in New Zealand, shipping is only $3. I think this is really just a good do-it-yourself solution, I’m not sure I would pay for this over the options that follow.
Another option is a series of stands from Scottish photo accessory company Modahaus, which they call Steady Stands. These stands are manufactured out of plastic, and are design to diffuse the light that hits the document or object inside the stand, which helps eliminate harsh shadows.
|Steady Stand 200|
The Steady Stand comes in a variety of sizes, and can be used to photograph physical objects, or used to create videos by dragging the whole stand over an object or document (such as a map) to create steady videos. I could see using the smaller one as a kind of Flip Pal replacement. The downside is that the FlipPal doesn’t need lighting, the plus side being that you don’t need to bring a full scanner with you, and the object you’re scanning doesn’t need to be flat. The smallest stand is £15 (yes, that’s British Pounds – currently about $23.37) and the largest is £31.20 (currently about $48.62)
The only solution I’ve seen that doesn’t shoot straight down onto a flat document, is the ScanJig. The ScanJig is also unique in that is designed to work with a larger variety of devices, from iPhones up to iPad Minis. There is a separate version for the Galaxy III and IV phones as well.
This is perhaps the most complicated stand in terms of setup. I’m not sure sure this is something I’d want to carry around with me. For some types of documents and workflows, this might be a good solution. I image if it’s on your desk and you’re copying lots of sheets of paper, this might be easier to swap out pages quickly. The ScanJig is currently $29.95 (although it says it is regularly $39.95) plus shipping (which was $4.95 to Boston).
One of the most interesting solutions is called the StandScan. It has two features that I really like – it folds flat, and it has the option to add LED lighting. Of course, due to its design that has opaque walls on three sides, it’s possible the LED lighting would be required to get good quality in many lighting situations, so maybe it’s not an option after all, but a requirement.
You can get the StandScan with or without the LED lighting, and there are two options for powering the lights, 9V (1 9V battery) or 12V (8 AA batteries). The stand without lighting is $19.95, the stand with lighting and a 9V battery pack is $29.95, and the scanner with lighting, both battery packs and an AC adapter is $37.95. Shipping seems to be $15, whether to the US or it seems anywhere in the world (and by that I mean I check how much it cost to ship to Israel).
One other option is Scandock, which is built like a more traditional copy stand, with built-in lights on overheard arms, and a weighted base. It has its own camera app, which uses color patches on the stand itself to insure proper color calibration, and the stand has a silicon cover for documents to insure they lay flat.
In short, the Scandock is much more advanced than the offerings above, but is also priced accordingly, which the cheapest version costing $279. Also, it’s not exactly a portable solution.
This device has a light source on the bottom, and you put in a transparency and scan it using your phone. It supports all iPhones and several Android devices. It has its own iPhone app, although you don’t need to use it (it is, however, helpful if the app you’re using can reverse the colors of image it captures).
The price is $59 in the US, and €59 in Europe, plus shipping. It’s also available for $59 (including shipping in the US) from photojojo, one of my favorite photo gadget companies.
Interestingly, two other phone stands were crowdfunded on Kickstarter, and succeeded in being shipped out (not as common as you might think with hardware products), but both seem to have disappeared – ScanBox and Scandy. The team behind ScanBox seems to have moved onto other products (LED light bulbs), while Scandy’s web site has disappeared completely.