Overview

NIH Image is a free, public-domain image processing and manipulation program for the Macintosh. It was developed by the Research Services Branch of the National Institutes of Health. The program can acquire, manipulate, analyze, and output images such as PICT, TIFF, PICS, and MacPaint graphics files. Where NIH Image really shines is in its ability to analyze images numerically to determine image measurements, such as area, mean pixel value, and perimeter. These functions are not usually available in free image-analysis programs, and they are excellent tools for the biological scientist. NIH Image can also interface with image-input systems through a range of plug-ins available from different sources (some are included). Additionally, NIH Image can be customized via macros, plug-ins, or through direct modification of the source code. Because the functions of this program require a reasonable understanding of image analysis, NIH Image is not for everyone. Yet NIH Image is a powerful tool for image analysis and, at the public-domain price, well worth the learning investment required to become proficient. I highly recommend this product for anyone who has sophisticated image-analysis needs.

How Long Did It Take to Learn to Use It Productively?

As with other image-manipulation programs, the basics of manipulation, such as the use of filters and image rotation, were easy to master for someone knowledgeable in image-manipulation techniques. But proficiency with all the included macros and plug-ins and with the menu-based image-analysis features requires extended use and experimentation. This program is not for the uninitiated. Expect to spend some time (a few hours) with the online manual and online tutorials to map known image-manipulation and analysis concepts to the software and functions. Those who are new to image analysis will find it difficult to use the program without patient study of the manual or tutorials. Finally, customization of the program requires a considerable knowledge of programming structures and procedures.

Product Quality

Customizability

Very good.

Ability to Program in Scripts, Add Extension Modules, etc.

Excellent.

Ability to Import and Export in Different File Formats

Good.

Useful or Unusual Features

NIH Image comes with a large collection of useful macros to aid in the analysis of images normally used by different branches of biomedicine. For example, there are macros for gel analysis, corpus-callosum analysis, MRI analysis, and particle analysis. There are also macros for animation, image math, fast Fourier transforms, and moviemaking. These macros take much of the guesswork and drudgery out of image analysis. For example, the Filters macro contains an extensive list of image-manipulation filters, such as 7 x 7 Gaussian or 5 x 5 Laplace convolutions. Some of these convolutions are also located in the Kernel folder with other standard convolutions. But the macros place the convolutions under an easy-to-use menu item. Finally, if the user is not content with the unmodified program, these macros are an excellent starting point for custom macros.

Real world example: I tried to analyze the band intensities of a 1-D gel using only the menu functions. It was laborious and repetitive, and I did not feel confident that my results were up to my standards. Then I tried the included Gel Analysis macro (and read the Gel Analysis tutorial). The procedure was fast, simple, and yielded much more reliable results, which I exported as a text file for graphing in another application.

There are a few hidden gems in the menus. A representative sample:

• A clever Draw Boundary item places a solid line around a selection. This feature is useful for marking actual areas of analysis.
• Draw Scale under the Edit menu and Draw Calibration Bar in the Plotting macro allow the user to place a grayscale bar for calibration onto the image. The macro even types in the values on the scale. Try doing that by hand.
• The Propagate menu item allows a set of colors and calibrations to be propagated to all other open windows. This is a great feature when dealing with a set of images that all need to be adjusted the same way.
• Under the Special menu are functions to set parameters for image capture.
• The Stacks menu contains all the functions needed to create a stack of images that can be displayed as animation or flipped through manually. Consecutive images, such as confocal serial sections, can also be captured directly into a stack. I did not test the capture feature.

Limitations

Many image grabbers are able to output a TIFF file. However, TIFF is the only cross-platform graphics format that NIH Image supports. This limited cross-platform support may be an issue, considering the prevalence of PC-based image-capture setups. On the output side, considering the increased use of the Web and Web graphics formats, NIH Image should support the export of JPEGs and GIFs.

NIH Image is extremely extensible via macros, plug-ins, and source code modification. Yet such customization requires a considerable knowledge of programming and programming structures. This places customizability beyond the reach of the lay user.

Due to the nature of the program (expert image analysis), the beginner without knowledge of image manipulation and analysis techniques faces a steep learning curve. Previous knowledge of image manipulation and analysis techniques is required to take advantage of all of the program's features. This is not a limitation, but users should be made aware of this issue.

Comparisons with Similar Software

To the extent of my knowledge, there are no other public-domain image-analysis packages that provide the same functions as does NIH Image (unless they are based on NIH Image). Comparable commercial packages are usually proprietary (bundled with image-capture devices) and expensive. Other versions of NIH Image, altered by third parties, have specialized functions worth looking into, such as adaptations specific to scanning-electron or confocal microscopes.

Technical Support and Documentation

There is a well-written online (Web and downloadable) user's manual for NIH Image. The Web site contains a large amount of helpful information and helps users find information and tutorials on topics such as densitometry and image capture. There is also a mailing list (with an archive reaching back many years) for discussion on NIH Image. Additionally, the author is available via email. Due to the freeware nature of the product, I do not think it is fair to expect telephone support. The resources available should help the user in distress to find a reasonable solution to any problem.

Target Users

The ideal user is someone who needs to capture images, either through NIH Image or separately, and analyze them. For example, the image manipulation and analysis features are beneficial to cell biologists analyzing microscope images or biochemists analyzing gels.