Image Resolution and You

Picking your resolution is perhaps the most important decision you'll make when digitizing photos, artwork, or any other kind of image. But it can also be confusing if you're not familiar with these terms and their meanings. This is a simple primer to help you choose the right resolution for your needs.

The terms DPI and PPI are both shorthand units for measuring an image's resolution. DPI stands for "dots per inch" and PPI, "pixels per inch." This means that DPI is technically a term for a printed object's resolution while PPI describes an image displayed on a screen, but in common use they are essentially interchangeable.

The system that these measurements describe is called Raster, and it's by far the most common in a modern digital setting. A raster image is essentially a mosaic, collecting dots of color called pixels in a tiny square grid to produce an overall image. The more pixels per inch, the more detailed the image. Simple enough, right? For an easy example, here is the same image at three different standard resolutions: 600dpi, 300dpi, and 72dpi (click to see at full size)

You can always lower the resolution of an image, but it's impossible to raise it, except in a simple multiplying sense. This is why all digital images look blurry if you zoom in far enough. You're making the pixels bigger, but you aren't adding any new information to them.

Another factor you will want to consider is your display resolution. Modern high-definition TVs will often give you this basic measurement, and while computers have a greater variety of resolutions they will generally fall under a few typical values. 480p means a screen is 480 pixels wide, and is considered "standard" definition. 720p is, of course, 720 pixels wide, and marks the beginning of "HD" standards. 1080p is probably the most commonly used HD resolution, and the cutting-edge "4K" resolution is a convenient shorthand for screens 3,840 pixels wide. The screen resolution will determine how "large any given image looks at full-resolution on the screen. If you try to stretch a 480p wide image across 1080 pixels, it will look bad.

While the ideas surrounding pixel resolution, display resolution, and print resolution are quite complicated, they can still be understood easily with a few guidelines. For most purposes you can create images using 3 different resolutions:

600ppi is what we at the Dartmouth Digital Library Program use as the standard for high quality "master" images. Although many scanners can go higher, the size of the file becomes very unwieldy at that point. My advice is to always start at at least 600. Better to have a high-quality image and not need it than to need it and not have it.

300ppi is a common resolution for a high-quality print. Unlike looking at a screen where the resolution can be shrunk or blown up, a printer is rigidly limited in the amount of detail it can put into any given area. While a particularly good printer may get higher resolutions, most will clock in around 300dpi. This lower resolution also makes transferring files for print easier. And of course, it's always useful to keep your higher-res files around in case you need to go back to them.

72ppi has become the most common display resolution on the internet. There are a few things to consider before simply converting your image into 72ppi. Look at your display, and understand what its resolution is. Then consider how "big" you want your image to look on the display. So, if you have a 1080p monitor and want an image that fills the whole screen, you'll want to change your ppi to 72, AND change your image width to 1080p at the same time, with the proportions locked.

Here we can see Photoshop's image size menu (Image -> Image Size), where the pixel width and resolution are changed while the proportions remain constrained.

This is often a confusing concept to grasp. The simplest way I can think of is: if you reduce a 300ppi image to 150ppi, but also double its size, it will essentially be the same image when you see it on your computer. But if you try to print that, it will be half as detailed by virtue of being twice as big.

Fortunately, you don't need to fully understand all of this in order to create and work with high-quality images. As long as you make sure your highest-quality 600ppi master versions are safely backed up, you can play around with these variables in Photoshop or any other imaging program until you meet your own needs. Understanding how screen resolution, print resolution, and image resolution work together is an ongoing process that changes with technology as well as peoples' needs. It's important to be consistent, especially so for an institution like ours, but it's equally important to know how to adapt to your own needs.

Written by Ryland Ianelli

Digital Production Roundup

Sometimes great content comes through the Digital Production offices and we don't have a chance to share it. Here are a few of my favorite selections from recent shooting sessions:

"The Flayed Angel" by Jacques Fabien Gautier D'Agoty, available to view in Rauner Special Collections. Read more about it here

A design for a theatrical device by Denis Diderot, co-founder/chief editor/contributor to the Encyclopédie with Jean le Rond d'Alembert

Vintage ad from Dartmouth Alum Robert L. May's scrapbook. May created the Rudolph character in 1939; read more about him here

Concert posters from Dartmouth history, scanned for an exhibit in the Baker Berry Library: Fleshtones concert poster, 1983

Spring Formal poster with Duke Ellington

New Hampshire maps from the Evans Map Room, scanned as part of the Granite State Maps project

Map illustrations

Written by Ryland Ianelli

The ABCs of Digital Preservation

April 27 through May 1 of this year marked the American Library Association's 5th Annual Preservation Week. To celebrate, I gave a talk for library staff titled The ABC's of Digital Preservation. The purpose of the talk was to introduce some basic digital preservation concepts, such as choosing file formats, file naming best practices, and the basics of preservation metadata. I also discussed some tools and models for managing digital materials, and tried to demystify some of the acronyms I throw around casually in meetings ("If we follow OAIS, the SIP could contain a TIF and some PREMIS and or METS, and of course the AIP will need an md5...").  You can view the slides of the talk here. 

The talk was well attended, and I got a lot of good feedback and follow-up questions. In this blog post, I'd like to address these questions, and talk about some resources to learn more about topics discussed in my presentation.

First, I'll start with some general resources...

In creating and organizing my presentation, I was inspired by the North Carolina Department of Cultural Resource's Digital Preservation Best Practices and Guidelines. It's a great resource and an excellent starting point.

Read through the archives and follow The Signal, the digital preservation blog of the Library of Congress. They highlight a lot of amazing projects covering all aspects of digital preservation.

Also, the North East Document Conservation Center has some great resources.

Now, on to your questions...

1. Is there a list of file formats defining their function that I could reference?

Yes! The Library of Congress developed this great resource for file format descriptions. The South Carolina Department of Archives and History also has a nice resource on File Formats.

2. Could you point me toward a bibliography of good guides for organizing photographs (or perhaps a workshop)?

Library of Congress's Personal Digital Archiving project has a good, succinct guide to archiving digital photos. Here's another great resource created by MLIS students at Catholic University of America for Preservation Week. Mike Ashenfelder also wrote a great blog post on The Signal answering questions about digital photo archiving (you should check out the webinar he references as well!) And finally, here is an amazing resource for digging into embedding metadata in digital images.

3. Can you tell me more about the Digital POWRR Tool Grid?

"The POWRR Tool Grid v2 provides a set of interactive views designed to help practitioners identify and select tools that they need to solve digital preservation challenges. This Grid is based on the Tool Grid first developed by the Digital POWRR Project, and combines the form and function of the original POWRR grid with the far greater coverage of tools provided by the COPTR data feed."

4. What are the current archival standard for image scans- resolution and bit depth?

The Federal Agencies Digitization Guidelines Initiative (FADGI!) has an excellent document that goes into great detail providing best practices for image scans:  Technical Guidelines for Digitizing Cultural Heritage Materials .  ALTCS, a division of ALA, has also published a helpful guide for Minimum Digitization Capture Recommendations for many types of media.

5. What are the best practices for preserving video files (ideal formats, codecs, etc.)?

Choosing a file format and codec for video preservation master files is complex. A lot depends on available resources, technological expertise, and the context in which files are created and managed. FADGI has done an excellent analysis of the issues involved in their report Digital File Formats for Digital Tape Reformatting. For best practice guidelines for creation and management of digital video, I really love the Activist's Guide to Archiving Video.

6. Bagit …. wait, what?
Check out this video from the Library of Congress. Another place to learn more is Bagit's wikipedia page. And if your ready to use BagIt, you can download it on Github.

7. What to do if a preservation copy has changed? Can you fix it?
Hopefully, you'll have multiple copies of a file, and the preservation copy can be replaced with a "good" one. For situations where this isn't the case, someone with expertise in the file format should be able to address the issue, as explained by @dericed:

8. What are some best practices or tools for data preservation?

A good place to start would be the How-to Guides and Checklists from the Digital Curation Centre. Then read through the rest of their website -- its a gold-mine of information on curating digital research! Library of Congress has recommended formats for datasets and databases, as well as a report on evaluating file formats for datasets and information on types of dataset file formats. Stanford also has a good guide covering many aspects of digital curation for research data. SCAPE is a project of the Open Preservation Foundation that develops software tools and training materials for large scale data preservation.

Written by Jenny Mullins

Baker Library in the Dartmouth College Photographic Files Collection

During the month of May, close to 1500 photographs of Baker Library were added to the Dartmouth College Photographic Files Collection. Included are many photos of the Baker Library building, interior and exterior, including its construction, as well as people that have worked here over many years. Here are some samples:

Baker Bery Under Construction

The Main Corridor

The Treasure Room

Baker Circulation Desk

Baker Library in Winter

View a much larger selection here.

The Dartmouth College Photographic Files project began in early 2012 and is part of the Dartmouth Digital Collections. The project's goal is to make over 80,000 photographs stored in file cabinets in Rauner Special Collections available online. Images date from the early years of photography (ca. 1850s) to the present and include images of nearly all aspects of Dartmouth College life. To date there are over 36,000 photos from the collection online. We add approximetly 1,000 photographs to the collection every month. We are working through the photographs alphabetically and have reached the letter "M". See additional photographs of Feldbery Library; Dana Biomedical Library and Kresge Library.

If you have questions about the Photographic Files Collection contact Rauner Special Collections If you have questions about the ditital imaging of the collection contact William B. Ghezzi or Ryland Ianelli in the Digial Production Unit.

Written by William B. Ghezzi

Merging Images in Photoshop, Part Two

While my first post in this series covered some basics of non-destructive image merging in Adobe Photoshop, this post aims to give you some tools to work with less ideal images.

A typical problem faced by many when attempting to merge images is how to deal with slight variations in your materials. These variations can be a result of the hardware you use (scanner or camera), lighting conditions, software, or a myriad other factors.

In this scenario I'll use an image from a scanned book that has a lighting problem. This is a very common difficulty when scanning books on a flatbed; the book's gutter will raise up from the scanner's surface, giving it a darker tone and distorting the content. Applying pressure to the book may work sometimes, but often we do not want to risk damaging our books (or, worst-case-scenario, our equipment) that way. Much safer to work digitally.

The first step is identifying the cutoff point where the gutter begins to negatively affect image quality. As you can see from this image. As always, make sure you've saved a master version before making any edits. 

Use the Rectangle Marquee tool to isolate the "safe zone" of the page, where the page's content is mostly unaffected by the gutter. Copy this selection and paste it into a new document with approximately the same dimensions as the original document. This is our new "base" document. I will usually put the word "EDIT" in its title somewhere so it won't be mistaken for the master.

In situations like this when we are dealing with an off-white paper, we'll want to make sure our background matches the paper's tone. Use the Eyedropper tool to select the page tone, and use the paint bucket to fill it in the background of the new base document.

What we are going to do next is create an amalgam of the image's two elements (page and background) to create a new version with improved legibility. To accomplish this we are going to use Photoshop's Layer Mask tool. Layer Mask is incredibly useful for photo editing, and best of all it is a non-destructive solution, meaning whatever you do with it can always be easily undone. The Layer Mask is very much what it sounds like: a layer placed on top of each image that can be "masked" or "unmasked," concealing or revealing the image's contents. Select the right side layer and click "Add Layer Mask" at the bottom of the Layer menu. You will now see a small white rectangle linked to that layer; that's your layer mask. The color white means "unmasked," so right now it's simply sitting on top of your original layer waiting for you to give it instructions.

Next, be sure you have the correct layer, AND your layer mask selected, or else you will alter the image itself. The Layer Mask functions in grayscale. Black is "masked," white is "unmasked," and grays are everything in between. Set your foreground color to black. Select the brush tool, and reduce the hardness to 0 (use whatever diameter you feel comfortable with). Check again to make sure you're still on your layer mask, and simply begin lightly touching up the problem spots along the gutter with your brush. Use single clicks rather than click-and-drag, that way you will make very minor adjustments while you get a feel for the technique.

As you can see, we've fixed the page to appear legible and flat. But be warned, this exact method won't work for every situation. If you have content that is deep in the book's gutters, you will likely have to accept a less-than-perfect image. However these techniques can still be used to improve the image quality in those situations, it is simply more difficult to get a "perfect" image. Vary your brush settings and color in the Layer Mask (experiment using a 50% grayscale) to find solutions that best suit your situation.

Written by Ryland Ianelli

Merging Images in Photoshop, Part One

One of the most common problems in digitization is how to deal with an image that is too big for your camera or scanner. The simplest solution is to photograph or scan the object in separate pieces, then merge those pieces together, however this can present its own set of problems to those unfamiliar with imaging software.

In this post I will be describing my own method for merging together images. There are many other ways to accomplish these tasks, and if you have a way that works for you, I encourage you to keep using it, but also be aware of its potential pitfalls. The main benefits of my own method are the ability to quality-check your work as you go, and make simple non-destructive edits that can be changed or reversed as needed. Also, for simplicity’s sake, I will be referring to my own Mac OS based workflow for menus and keyboard shortcuts.

Here is the whole image that we’re trying to assemble, and for whatever reason, it’s been captured in two side-by-side pieces in the standard .tiff format. It is crucially important, when capturing, to make sure there is overlap between the captures. This is going to help us check how well-aligned our merging is, so the more overlap the better.

Notice how each side is wider than half of the image

Now that we’ve got our two images, open both in Adobe Photoshop and choose whichever one you want to start working on. I usually go from left to right for simplicity’s sake, so here I will be starting on the left side of the image.

In Photoshop, select the Image drop-down file menu, and select “Canvas Size…” (or use the keyboard shortcut: option+command+C). Click on the canvas width field, and double it. In the “Anchor” field, select the leftmost column of the grid so that Photoshop knows where to put the empty space.

You should be left with an image like this:

It will end up a little wider than is necessary, but it’ll be easier to trim it down after the fact than to add more space. This will now become our “master” file. Do a “Save As” at this point and designate it as such.

Next, go to the second image that we are going to merge into the master (in this case, the right side image). The next step should be familiar to most computer users: select all of the image (command+A), and copy it to the clipboard (command+C). Then go back to the master file and use paste (command+V) to add it into the image.

If you’re paying attention, you’ll obviously notice that this new image is not in the correct position. However, by looking at the Layers panel on the right side of Photoshop you’ll see that the new image is on its own layer, resting on top of the background (if you do not see the Layers panel, select the “Window” drop-down menu and enable “Layers” there). Thus we can edit it without disturbing the original “bottom” layer.

Now, with the top layer selected, click on the “Opacity” field in the Layers panel and set it to 40%. This will make the top layer semi-transparent and allow us to line it up with the bottom layer.

Then, with the Move tool selected (V), begin moving the top layer around and trying to find where it lines up. Look for any solid shapes that are shared by both images, or where the borders intersect. Letterforms provide nice clear and easily-spottable shapes, which is why I have used them in this example, but it can be anything so long as it’s shared by both images.

We’re getting there, but it’s obviously still not right. At this point, find an area of overlap and zoom in closely. Then, with both the top layer and the move tool selected, simply “nudge” the top layer into place using the arrow keys. The arrow keys will only move the layer one pixel at a time, so obviously this is for the finest level of adjustments.

Almost...

Nailed it!

Now for the final steps! In the layers panel, set the top layer’s opacity back to 100%. Then inspect the images along the borders, making sure that it looks seamless. While checking for quality be sure to zoom in and out.

At this point you can crop the image down to its original size, and it will be ready to go. However, one important piece to remember is that layered .tiffs, in addition to simply being larger files, are also not commonly supported by web or other software. What I like to do at this point is to save the “Master” file with both layers, and then create a new version for common use. The common use version will get flattened (Layer -> Flatten Image) then do a Save As in whatever format is required such as .jpeg or .pdf. This way, if any changes need to be made, we can always go back to the Master version.

And there you have it! A nice, seamless image. In the next post in this series, I will go into more detail for dealing with other problems, such as skew and mismatched backgrounds or details.

Written by Ryland Ianelli

Dartmouth Library Joins the National Digital Stewardship Alliance

We are very excited to announce that Dartmouth College Library has joined the National Digital Stewardship Alliance (NDSA), a consortium of organizations that are committed to the long-term preservation of digital information. The mission of the NDSA is to establish, maintain, and advance the capacity to preserve our nation's digital resources for the benefit of present and future generations. Members include universities, consortia, professional societies, commercial businesses, professional associations, and government agencies at the federal, state, and local level.

The NDSA is organized into 5 working groups: Content, Standards and Practices, Infrastructure, Innovation, and Outreach. Each group develops and executes a series of projects, which have included:

·         Developing the Levels of Preservation, a set of guidelines on tiered levels of digital preservation (Infrastructure WG)

·         Publishing a report on "Issues in the Appraisal and Selection of Geospatial Data"  (Content WG)

·         Creating Digital Preservation in a Box, a toolkit to support outreach activities that introduce the basic concepts of preserving digital information (Outreach WG)

·         Recognizing innovation in the community through the NDSA Innovation Awards (Innovation WG)

I am very excited to join the Standards and Practices Working Group, which works to "facilitate a community-wide understanding of the role and benefit of standards in digital preservation and how to use them effectively to ensure durable and usable collections." Projects undertaken by this group include a report on "The Benefits and Risks of the PDF/A-3 File Format for Archival Institutions" and a recent survey assessing stumbling blocks for video preservation.

Written by Jenny Mullins

Dartmouth at the Digital Directions 2014 Conference

Image from the blog PDXretro.com

This past July I had the great opportunity to attend the Northeast Document Conservation Center’s Digital Directions 2014 conference. In a lucky turn, this year’s conference was held in Portland, Oregon, home of my alma mater, Reed College. In addition to reexperiencing the highlights of one of my favorite American cities, I was able to meet and engage with many people doing amazing work in digital collections across the country and beyond.

The conference covered a fascinating diversity of topics, from high-level project management and planning to specific examples of workflows and equipment setups. One of the first things impressed upon me was the fascinating diversity of digitization efforts occurring across the world. As the demand for digital content continues to expand, many institutions are rushing to fill that need. Because of this, it can often seem that no two institutions’ digital programs are the same, or even particularly similar.

To its credit, the Digital Directions did a phenomenal job accounting for these various setups. The three days were jam-packed with a fascinating variety of discussion topics and presentations. The first day consisted of mostly big-picture type talks. We discussed the interplay between digital preservation (maintenance of access to digital content) and digital curation (adding value to digital content), as well as how to craft each institution’s best practices and standards according to their needs. The day was wrapped up with an impressively no-nonsense discussion about rights and responsibilities from a legal perspective by Peter Hirtle, followed by a lovely meet-and-greet at the Portland Art Museum.

The following days covered a wide variety of topics, including a fascinating section about audio and video digitization (an area unfortunately outside my range of experience). However, it soon became apparent that the challenges faced by those audio and video digitization teams were remarkably similar to my own in the world of object and document reproduction. Many digitization projects face the same fundamental roadblocks: time, equipment, resources, access, and storage.

Image from NEDCC's twitter account

While the specifics varied, these fundamental issues could not help but make themselves apparent. The relative merits of, say, cloud storage (to pick a random example), can be endlessly debated among digital librarians, and indeed I’d doubt there ever will be a definitive final-word on this topic. But the crucial takeaway must be a willingness to engage with these issues, understanding the risks and drawbacks inherent in each option so that they can be minimized, or at the very least understood fully so that we may deal with them more effectively in the future. Among the many useful things I learned at Digital Directions 2014, perhaps the most important one was that my own peers are an incredible resource, both within Dartmouth and world-wide. By learning through their experiences and sharing my own, I hope to do my part to keep the Dartmouth Library’s Digital Collection growing and improving well into the future.

Written by Ryland Ianelli

100-ish Days of Digital Preservation

Hello, there. It's been a little over 100 days since I started as Dartmouth College Library's first Digital Preservation Librarian. I've been working closely with staff in many departments to define my role and work out how best to ensure long term access to the Library's digital content. Here are some of the things that I've been up to:

• Maxed out our master file server space.
• Learned about awesome projects and connected with colleagues at Digital Preservation 2014.
• Made some head-way into assessing our e-resource preservation strategies.
• Used BagIt to package 45,000 files totaling 2413 GB for long-term storage (see above re: maxing out server space).
• Started digging into PREMIS .
• Learned to harness the power of Twitter for professional research #digipres .
• Started brainstorming strategies for preserving analog and born-digital a/v content.
• Dipped my toes into web and database preservation in response to a faculty inquiry.
• Got really excited about sustainability and digital humanities projects.

Digital Preservation Brainstorming!

 I’m looking forward to my role in the Library continuing to evolve and grow over time. As these and other projects develop, I will tell you all about them here. Stay tuned for the next 100-ish days of Digital Preservation!

Written by Jennifer Mullins

Digital Production Unit Update, Part 2

The primary focus of the Digital Production Unit over the past few months has been to incorporate the new reprographic system into our workflows. Since we started using the new equipment in January we have been able to take advantage of its speed and high quality imaging in a number of projects. 

We have redesigned our workflow for the Dartmouth College Photographic Files collection to use the new camera exclusively. The previous workflow for this ongoing project used two scanners on two computers and required additional post production work to gather all of the images together. Our new workflow consolidates all of that work onto one workstation. The streamlined workflow has created noticeable positive effects in the time it takes to complete work on this project.

Dartmouth College Photographic Files collection: (http://libarchive.dartmouth.edu/cdm/search/collection/photofiles/collection)

One of the first projects we tackled with the new equipment was to shoot recent Winter Carnival Posters. This was a great learning opportunity for us. The posters are large and colorful and gave us a chance to develop our skills with the hardware and software. We will add individual new posters as they become available in future Winter terms. In addition, we are in the planning stages of a project to reshoot all of the posters to upgrade the quality of our master images.

Dartmouth Winter Carnival Posters:(http://www.dartmouth.edu/~library/digital/collections/other/WinterCarnivalPosters.html)

We have also been able to use the equipment in support of smaller projects in Rauner Special Collections and for exhibits by Education and Outreach. Other work with the camera includes one-offs for various projects, quality assurance and corrections.

In other news, we continue to redesign our work area. We recently moved all of the scanning equipment into room 2D, turning that space into our scanning lab.

By Willliam B. Ghezzi

Preservation Week: Caring for Audio Files

During Preservation Week libraries all over the country present events, activities, and resources that highlight what we can do, individually and together, to preserve our personal and shared collections.

Preservation Tip:
Sound:

Many listeners have migrated their music CDs to their computers. Care for the computer music files as you would all digital files. For those who still maintain a CD collection, store your discs vertically as in a bookshelf in their original packaging. Protect discs from scratches and fingermarks by handling with care and put back in their cases after listening. If creating your own music discs label them with a non-solvent pen created for this purpose rather than a label.

For more information check out www.cool.conservation-us.org/bytopic/audio/