Free, Open Source Optical Character Recognition with gImageReader

Posted on November 5, 2020 by Ben Ostermeier

Optical Character Recognition (OCR) is a powerful tool to transform scanned, static images of text into machine-readable data, making it possible to search, edit, and analyze text. If you’re using OCR, chances are you’re working with either ABBYY FineReader or Adobe Acrobat Pro. However, both ABBYY and Acrobat are propriety software with a steep price tag, and while they are both available in the Scholarly Commons, you may want to perform OCR beyond your time at the University of Illinois.

Thankfully, there’s a free, open source alternative for OCR: Tesseract. By itself, Tesseract only works through the command line, which creates a steep learning curve for those unaccustomed to working with a command-line interface (CLI). Additionally, it is fairly difficult to transform a jpg into a searchable PDF with Tesseract.

Thankfully, there are many free, open source programs that provide Tesseract with a graphical user interface (GUI), which not only makes Tesseract much easier to use, some of them come with layout editors that make it possible to create searchable PDFs. You can see the full list of programs on this page.

The program logo for gImageReader

In this post, I will focus on one of these programs, gImageReader, but as you can see on that page, there are many options available on multiple operating systems. I tried all of the Windows-compatible programs and decided that gImageReader was the closest to what I was looking for, a free alternative to ABBYY FineReader that does a pretty good job of letting you correct OCR mistakes and exporting to a searchable PDF.

Installation

gImageReader is available for Windows and Linux. Though they do not include a Mac compatible version in the list of releases, it may be possible to get it to work if you use a package manager for Mac such as Homebrew. I have not tested this though, so I do not make any guarantees about how possible it is to get a working version of gImageReader on Mac.

To install gImageReader on Windows, go to the releases page on Windows. From there, go to the most recent release of the program at the top and click Assets to expand the list of files included with the release. Then select the file that has the .exe extension to download it. You can then run that file to install the program.

Manual

The installation of gImageReader comes with a manual as an HTML file that can be opened by any browser. As of the date of this post, the Fossies software archive is hosting the manual on its website.

Setting OCR Mode

gImageReader has two OCR modes: “Plain Text” and “hOCR, PDF”. Plain Text is the default mode and only recognizes the text itself without any formatting or layout detection. You can export this to a text file or copy and paste it into another program. This may be useful in some cases, but if you want to export a searchable PDF, you will need to use hOCR, PDF mode. hOCR is a standard for formatting OCR text using either XML or HTML and includes layout information, font, OCR result confidence, and other formatting information.

To set the recognition to hOCR, PDF mode, go to the toolbar at the top. It includes a section for “OCR mode” with a dropdown menu. From there, click the dropdown and select hOCR, PDF:

This is the toolbar for gImageReader. You can set OCR mode by using the dropdown that is the third option from the right.

Adding Images, Performing Recognition, and Setting Language

If you have images already scanned, you can add them to be recognized by clicking the Add Images button on the left panel, which looks like a folder. You can then select multiple images if you want to create a multipage PDF. You can always add more images later by clicking that folder button again.

On that left panel, you can also click the Acquire tab button, which allows you to get images directly from a scanner, if the computer you’re using has a scanner connected.

Once you have the images you want, click the Recognize button to recognize the text on the page. Please note that if you have multiple images added, you’ll need to click this button for every page.

If you want to perform recognition on a language other than English, click the arrow next to Recognize. You’ll need to have that language installed, but you can install additional languages by clicking “Manage Languages” in the dropdown appears. If the language is already installed, you can go to the first option listed in the dropdown to select a different language.

Viewing the OCR Result

In this example, I will be performing OCR on this letter by Franklin D. Roosevelt:

Raw scanned image of a typewritten letter signed by Franklin Roosevelt

This 1928 letter from Franklin D. Roosevelt to D. H. Mudge Sr. is courtesy of Madison Historical: The Online Encyclopedia and Digital Archive for Madison County Illinois. https://madison-historical.siue.edu/archive/items/show/819

Once you’ve performed OCR, there will be an output panel on the right. There are a series of buttons above the result. Click the button on the far right to view the text result overlaid on top of the image:

The text result of performing OCR on the FDR letter overlaid on the original scan.

Here is the the text overlaid on an image of the original scan. Note how the scan is slightly transparent now to make the text easier to read.

Correcting OCR

The OCR process did a pretty good job with this example, but it there are a handful of errors. You can click on any of the words of text to show them on the right panel. I will click on the “eclnowledgment” at the end of the letter to correct it. It will then jump to that part of the hOCR “tree” on the right:

hOCR tree in gImageReader, which shows the recognition result of each word in a tree-like structure.

The hOCR tree in gImageReader, which also shows OCR result.

Note in this screenshot I have clicked the second button from the right to show the confidence values, where the higher the number, the higher the confidence Tesseract has with the result. In this case, it is 67% sure that eclnowledgement is correct. Since it obviously isn’t correct, we can type new text by double-clicking on the word in this panel and type “acknowledgement.” You can do this for any errors on the page.

Other correction tips:

If there are any regions that are not text that it is still recognizing, you can right click them on the right and delete them.
You can change the recognized font and its size by going to the bottom area labeled “Properties.” Font size is controlled by the x_fsize field, and x_font has a dropdown where you can select a font.
It is also possible to change the area of the blue word box once it is selected, simply by clicking and dragging the edges and corners.
If there is an area of text that was not captured by the recognition, you can also right click in the hOCR “tree” to add text blocks, paragraphs, textlines, and words to the document. This allows you to draw a box on image and then type what the text says.

Exporting to PDF

Once you are done making OCR corrections, you can export to a searchable PDF. To do so, click the Export button above the hOCR “tree,” which is the third button from the left. Then, select export to PDF. It then gives you several options to set the compression and quality of the PDF image, and once you click OK, it should export the PDF.

Conclusion

Unfortunately, there are some limitations to gImageViewer, as can often be the case with free, open source software. Here are some potential problems you may have with this program:

While you can add new areas to recognize with OCR, there is not a way to change the order of these elements inside the hOCR “tree,” which could be an issue if you are trying to make the reading order clear for accessibility reasons. One potential workaround could be to use the Reading Order options on Adobe Acrobat, which you can read about in this libguide.
You cannot show the areas of the document that are in a recognition box unless you click on a word, unlike ABBYY FineReader which shows all recognition areas at once on the original image.
You cannot perform recognition on all pages at once. You have to click the recognition button individually for each page.
Though there are some image correction options to improve OCR, such as brightness, contrast, and rotation, it does not have as many options as ABBYY FineReader.

gImageViewer is not nearly as user friendly or have all of the features that ABBYY FineReader has, so you will probably want to use ABBYY if it is available to you. However, I find gImageViewer a pretty good program that can meet most general OCR needs.

Scholarly Commons Software: Open Source Alternatives

Posted on March 19, 2020 by Mallory E. Untch

Hello from home to all my fellow (new) work-from-homers!

In light of measures taken to protect public health, it can feel as though our work schedules have been shaken up. However, we are here to help you get back on track and the first thing to do is make sure you have all the tools necessary to be successful at home.

Continue reading →

A Brief Explanation of GitHub for Non-Software-Developers

Posted on October 17, 2019 by Abigail Sewall

GitHub is a platform mostly used by software developers for collaborative work. You might be thinking “I’m not a software developer, what does this have to do with me?” Don’t go anywhere! In this post I explain what GitHub is and how it can be applied to collaborative writing for non-programmers. Who knows, GitHub might become your new best friend.

You don’t need to be a computer wiz to get Git.

Picture this: you and some colleagues have similar research interests and want to collaborate on a paper. You have divided the writing work to allow each of you to work on a different element of the paper. Using a cloud platform like Google Docs or Microsoft Word online you compile your work, but things start to get messy. Edits are made on the document and you are unsure who made them or why. Elements get deleted and you do not know how to retrieve your previous work. You have multiple files saved on your computer with names like “researchpaper1.dox”, “researchpaper1 with edits.dox” and “research paper1 with new edits.dox”. Managing your own work is hard enough but when collaborators are added to the mix it just becomes unmanageable. After a never ending reply-all email chain and what felt like the longest meeting of all time, you and your colleagues are finally on the same page about the writing and editing of your paper. It just makes you think, there has got to be a better way to do this. Issues with collaboration are not exclusive to writing, they happen all the time in programming, which is why software-developers came up with version control systems like Git and GitHub.

Gif of Spongebob running around an office on fire with paper and filing cabinets on the floor

Managing versions of your work can be stressful. Don’t panic because GitHub can help.

GitHub allows developers to work together through branching and merging. Branching is the process by which the original file or source code is duplicated into clone files. These clones contain all the elements already in the original file and can be worked in independently. Developers use these clones to write and test code before combining it with the original code. Once their version of the code is ready they integrate or “push” it into the source code in a process called merging. Then, other members of the team are alerted of these changes and can “pull” the merged code from the source code into their respective clones. Additionally, every version of the project is saved after changes are made, allowing users to consult previous versions. Every version of your project is saved with with descriptions of what changes were made in that particular version, these are called commits. Now, this is a simplified explanation of what GitHub does but my hope is that you now understand GitHub’s applications because what I am about to say next might blow your mind: GitHub is not just for programmers! You do not need to know any coding to work with GitHub. After all, code and written language are very similar.

Even if you cannot write a single line of code, GitHub can be incredibly useful for a variety of reasons:
1. It allows you to electronically backup your work for free.
2. All the different versions of your work are saved separately, allowing you to look back at previous edits.
3. It alerts all collaborators when a change is made and they can merge that change into their own versions of the text.
4. It allows you to write using plain text, something commonly requested by publishers.

Hopefully, if you’ve made it this far into the article you’re thinking, “This sounds great, let’s get started!” For more information on using GitHub you can consult the Library’s guide on GitHub or follow the step by step instructions on GitHub’s Hello-World Guide.

Gif of man saying "check it out" and pointing to the right.

There are many resources on getting started with GitHub. Check them out!

Here are some links to what others have said about using GitHub for non-programmers:

Top Ten Reason GitHub is a Great Tool for Creative Writers by JJ Merelo
Git for writers: Write fiction like a (good) programmer by Vanessa Guedes
How writers can get work done better with Git by Seth Kenlon
Git for Non-Programmers: How to use Git/GitHub as a non-technical person from Jarboo

Google MyMaps Part II: The Problem with Projections

Posted on February 6, 2019 by Michael Cummings

Back in October, we published a blog post introducing you to Google MyMaps, an easy way to display simple information in map form. Today we’re going to revisit that topic and explore some further ways in which MyMaps can help you visualize different kinds of data!

One of the most basic things that students of geography learn is the problem of projections: the earth is a sphere, and there is no perfect way to translate an image from the surface of a sphere to a flat plane. Nevertheless, cartographers over the years have come up with many projection systems which attempt to do just that, with varying degrees of success. Google Maps (and, by extension, Google MyMaps) uses perhaps the most common of these, the Mercator projection. Despite its ubiquity, the Mercator projection has been criticized for not keeping area uniform across the map. This means that shapes far away from the equator appear to be disproportionately larger in comparison with shapes on the equator.

Luckily, MyMaps provides a method of pulling up the curtain on Mercator’s distortion. The “Draw a line” tool, , located just below the search bar at the top of the MyMaps screen, allows users to create a rough outline of any shape on the map, and then drag that outline around the world to compare its size. Here’s how it works: After clicking on “Draw a line,” select “Add line or shape” and begin adding points to the map by clicking. Don’t worry about where you’re adding your points just yet, once you’ve created a shape you can move it anywhere you’d like! Once you have three or four points, complete the polygon by clicking back on top of your first point, and you should have a shape that looks something like this:

Now it’s time to create a more detailed outline. Click and drag your shape over the area you want to outline, and get to work! You can change the size of your shape by dragging on the points at the corners, and you can add more points by clicking and dragging on the transparent circles located midway between each corner. For this example, I made a rough outline of Greenland, as you can see below.

You can get as detailed as you want with the points on your shapes, depending on how much time you want to spend clicking and dragging points around on your computer screen. Obviously I did not perfectly trace the exact coastline of Greenland, but my finished product is at least recognizable enough. Now for the fun part! Click somewhere inside the boundary of your shape, drag it somewhere else on the map, and see Mercator’s distortion come to life before your eyes.

Here you can see the exact same shape as in the previous image, except instead of hovering over Greenland at the north end of the map, it is placed over Africa and the equator. The area of the shape is exactly the same, but the way it is displayed on the map has been adjusted for the relative distortion of the particular position it now occupies on the map. If that hasn’t sufficiently shaken your understanding of our planet, MyMaps has one more tool for illuminating the divide between the map and reality. The “Measure distances and areas” tool, , draws a “straight” line between any two (or more) points on the map. “Straight” is in quotes there because, as we’re about to see, a straight line on the globe (and therefore in reality) doesn’t typically align with straight lines on the map. For example, if I wanted to see the shortest distance between Chicago and Frankfurt, Germany, I could display that with the Measure tool like so:

The curve in this line represents the curvature of the earth, and demonstrates how the actual shortest distance is not the same as a straight line drawn on the map. This principle is made even more clear through using the Measure tool a little farther north.

The beginning and ending points of this line are roughly directly north of Chicago and Frankfurt, respectively, however we notice two differences between this and the previous measurement right away. First, this is showing a much shorter distance than Chicago to Frankfurt, and second, the curve in the line is much more distinct. Both of these differences arise, once again, from the difficulty of displaying a sphere on a flat surface. Actual distances get shorter the closer you get to the north (or south) ends of the map, which in turn causes all of the distortions we have seen in this post.

How might a better understanding of projection systems improve your own research? What are some other ways in which the Mercator projection (or any other) have deceived us? Explore for yourself and let us know!

An Introduction to Google MyMaps

Posted on October 24, 2018 by Michael Cummings

Geographic information systems (GIS) are a fantastic way to visualize spatial data. As any student of geography will happily explain, a well-designed map can tell compelling stories with data which could not be expressed through any other format. Unfortunately, traditional GIS programs such as ArcGIS and QGIS are incredibly inaccessible to people who aren’t willing or able to take a class on the software or at least dedicate significant time to self-guided learning.

Luckily, there’s a lower-key option for some simple geospatial visualizations that’s free to use for anybody with a Google account. Google MyMaps cannot do most of the things that ArcMap can, but it’s really good at the small number of things it does set out to do. Best of all, it’s easy!

How easy, you ask? Well, just about as easy as filling out a spreadsheet! In fact, that’s exactly where you should start. After logging into your Google Drive account, open a new spreadsheet in Sheets. In order to have a functioning end product you’ll want at least two columns. One of these columns will be the name of the place you are identifying on the map, and the other will be its location. Column order doesn’t matter here- you’ll get the chance later to tell MyMaps which column is supposed to do what. Locations can be as specific or as broad as you’d like. For example, you could input a location like “Canada” or “India,” or you could choose to input “1408 W. Gregory Drive, Urbana, IL 61801.” The catch is that each location is only represented by a marker indicating a single point. So if you choose a specific address, like the one above, the marker will indicate the location of that address. But if you choose a country or a state, you will end up with a marker located somewhere over the center of that area.

So, let’s say you want to make a map showing the locations of all of the libraries on the University of Illinois’ campus. Your spreadsheet would look something like this:

Once you’ve finished compiling your spreadsheet, it’s time to actually make your map. You can access the Google MyMaps page by going to www.google.com/mymaps. From here, simply select “Create a New Map” and you’ll be taken to a page that looks suspiciously similar to Google Maps. In the top left corner, where you might be used to typing in directions to the nearest Starbucks, there’s a window that allows you to name your map and import a spreadsheet. Click on “Import,” and navigate through Google Drive to wherever you saved your spreadsheet.

When you are asked to “Choose columns to position your placemarks,” select whatever column you used for your locations. Then select the other column when you’re prompted to “Choose a column to title your markers.” Voila! You have a map. Mine looks like this:

At this point you may be thinking to yourself, “that’s great, but how useful can a bunch of points on a map really be?” That’s a great question! This ultra-simple geospatial visualization may not seem like much. But it actually has a range of uses. For one, this type of visualization is excellent at giving viewers a sense of how geographically concentrated a certain type of place is. As an example, say you were wondering whether it’s true that most of the best universities in the U.S. are located in the Northeast. Google MyMaps can help with that!

This map, made using the same instructions detailed above, is based off of the U.S. News and World Report’s 2019 Best Universities Ranking. Based on the map, it does in fact appear that more of the nation’s top 25 universities are located in the northeastern part of the country than anywhere else, while the West (with the notable exception of California) is wholly underrepresented.

This is only the beginning of what Google MyMaps can do: play around with the options and you’ll soon learn how to color-code the points on your map, add labels, and even totally change the appearance of the underlying base map. Check back in a few weeks for another tutorial on some more advanced things you can do with Google MyMaps!

Try it yourself!

Commons Knowledge

Insights from the Scholarly Commons

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