Preparing effective medical illustrations for publication (Part 2): software processing, drawing and illustration
Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
This is the second part of an article on preparing images
for medical publication. The first part dealt with optimal capture and export
of pixel-based medical images. This part will deal with post-processing and
editing of such images using specific software tools, and with the use of
graphics illustration and charting software applications for creation of medical
illustrations and charts.
In the last 20 years, increasingly powerful computer
software and hardware has become available to the general public, and the
now-pervasive ability to create digital images through electronic radiology
image archives, digital photography, scanning of paper or film and graphics
software for charting and illustration, have meant that the once-arcane art of
graphic design and medical illustration have become democratised and at least
for many types of illustration, is no longer the province of the expert graphic
artist. This is not to say that we can all become professional artists, but
rather that the simpler tasks of medical illustration are now within the reach
of the ordinary person with sufficient knowledge, tools, training and practice.
This article highlights and describes important approaches
to producing high quality medical illustrations for publication, which has
differing requirements to electronic, web-based or computer presentations. As
such, it will cover general preparation, the types of illustration needed, key
software that should be used, and some basic concepts and techniques that
anyone preparing their own images should be familiar with.
If there is a key principle to be remembered by would-be
authors, it is this: the published illustration should be able to stand
alone. In short, if the illustration cannot be understood in the absence of
any explanation other than the accompanying caption, it is incomplete. Thus, a
chart usually needs a title and/or subtitle, legend and sometimes data points
to be highlighted. A medical image or set of images often need alphanumeric
identification and appropriate arrows or other symbols highlighting specific
features. And drawings usually require labels attached to various elements.
Furthermore, simplicity is crucial. It is very important
for anyone in the target audience to be able to rapidly grasp what the
illustration is meant to show, ideally without reading the caption (this
is particularly true for charts and tables). Complex graphics and illustrations
will generally not be understood without intensive study, unless there is
appropriate division of information presentation. For many charts in
particular, careful selection of the type of graphic for the data is important
to ensure that the presentation is not only meaningful but avoids distracting
and sometimes misleading graphic �embroidery� which is so easily applied using
current charting packages. For scientific applications, dedicated scientific
charting packages are to be preferred to business-style charts available in
spreadsheet software such as Microsoft Excel.
Today, all illustrations are digital in nature, or become
so in the course of publication preparation, simply because publishing technology
is now universally digital, with all journals now laid out using computers and
dedicated professional software tools. There are two types of graphics used for
illustration: pixel-based images and vector graphics. Typically all such
publications require that digital graphics are submitted in a finalised form
suitable for placement, with specific resolutions and file formats which can be
used directly for page layout. Regardless of the original type of image, the
submitted images for publication are typically pixel-based image files (usually
tagged image file format, or TIFF) at the resolution required by the publisher.
The majority of images for eventual publication will have to be exported to
this format, as it is rarely used for primary image capture or illustration
creation. However, its universality in all imaging software and innately
lossless image storage format means it is ideal for the final common step prior
Pixel-based graphic acquisition and capture was dealt with
in Part 1 of this 2-part article. Even when captured from the original source,
these images usually require re-sizing to a specific pixel resolution and size,
grey-scale manipulation, and almost always need some on-image indicators and
annotation (alphanumeric characters, asterisks, arrows etc.) prior to export
for publication. Typically software such as Adobe Photoshop is used for this
purpose. Some basic rules should be followed to minimise any loss of quality
during image manipulation with such software; these guidelines are described
Vector images differ substantially from pixel-based
images. In digital form they are resolution-independent, and can be scaled
almost infinitely in size without any reduction in quality. They are created
using mathematically defined primitive objects such as lines, arcs, rectangles
and bezier curves, with mathematically defined shading, line width, colours
etc, by either charting packages such as DeltaGraph or Kaleidagraph, or graphic
illustration packages such as Adobe Illustrator. Because these packages have
proprietary formats, the images must be exported to common pixel-based formats
prior to publication; the author must render them to a specific size and pixel
resolution suitable for printing. Typically this is done by one of 3 methods:
- Exporting to Adobe Portable Document Format (PDF) to a specified size;
this usually requires the purchase of Adobe Acrobat.
- Export directly to Tagged Image File Format (TIFF) to the specified
resolution; this is usually possible without additional cost
- Export to Adobe Encapsulated Postscript (EPS), with subsequent rendering
of the image using Adobe Photoshop by the publisher to the resolution required;
again this usually does not require any additional cost
The last option gives the author and the publisher the
most flexibility, but is rarely used except by professional illustrators.
The ubiquity and power of Adobe�s Photoshop software for
image editing has led to a justifiably legendary reputation. However, the full
version of Photoshop is overkill for the vast majority of tasks the radiologist
needs to create useful images for presentation or publication. There are some
much cheaper alternatives for the more casual user, which have the benefit of a
shorter learning curve and sometimes much simpler methods of performing common
The best of these is probably Adobe�s much cheaper
Photoshop Elements, which for routine tasks is the equal of the full product.
Free or low cost shareware alternatives are also widely available on the
internet; GIMP (the GNU Image Manipulation Program) is a well known example of
very powerful, open-source, free image manipulation software. However, this is
actually somewhat more complex to learn than Photoshop.
A major advantage of the Photoshop family of products,
including Photoshop Elements, is the ability to use a huge range of third party
plug-in software tools to facilitate image correction. These include software
for RAW format conversion, for removing or reducing image noise, for correcting
lens distortion in digital photographs, and for more accurate interpolation
when enlarging an image (Photoshop�s internal algorithms show significant
artifacts for enlargement factors of 200% or greater).
This is required in virtually every medical image that is
captured, regardless of how it was obtained. The exposure, brightness and
contrast may adjusted for the screen but not be optimal for printing. There may
be image distortion or noise. The image may be too large or too small and
require scaling and resizing. Text on the image (e.g., patient name and ID,
examination details) or artifacts such as greaseproof pencil marks, scratches
and reflections may need to be removed (particularly so with images
photographed from hardcopy film printing) or appropriate markers and text
inserted (e.g., arrows, stars and alphanumeric indicators of specific
features). One universal step for publication is the need for image sharpening;
unless this is done, even the best images tend to be reproduced appearing
slight �soft� and blurred due to the screen and printing process.
Virtually every images must undergo multiple editing
steps, leaving any resizing and sharpening effects to the last as these
are destructive, and if done too early cause major artefacts subsequently (See
Figures 1 to 8). Specific tool terminology used here refers to Adobe Photoshop
naming conventions unless otherwise stated.
- Correcting lens distortions (e.g., LensFix)
- Levels adjustment for overall brightness and contrast
- Cropping or masking image to desired region
- Editing small regions to remove artifacts using the brush, stamp and
healing brush tools
- Enhancing various features using lasso and mask selection and various
- Resizing to final desired size; this may require special software tools
to ensure minimum loss of quality (e.g., pixl Smartscale, PhotoZoom Pro)
- Adding text, stars or arrows as required
- Sharpening, using Unsharp Mask or similar tool
- Saving file with layers in native or multilayer TIFF format for redo
- Saving or exporting to TIFF without layers for publication
For maximal flexibility, most modern pixel editing
software support the use of layers to perform these editing tasks. This is
nondestructive to the underlying original image, permits re-do editing at any
time, and can be used to create a �flattened� final image for publication once
all final adjustments have been made. It is well worth learning to use this
feature for many image editing applications.
Most images for publication in a medical journal require
some text, arrows and other indicators to be overlaid on the image to highlight
specific features for discussion.
In the past, adhesive precut lettering and symbols (e.g.,
Letraset) would be rubbed onto a camera-ready photograph by the author prior to
sending the article for review.
As noted above, it is possible to use Photoshop to create
layers of text and symbols to overlay the image, and to send this to the
publisher. In general, although it is possible to flatten the file as described
above, it is usually important to try to use resolution independent text rather
than to fix the resolution of the text with the image file.
Typically this issue can be problematic for both the
author and the publisher. However, the ubiquity of Microsoft Office�s
Powerpoint software application has recently led some publishers to request
that all publication images to be sent in the form of Powerpoint files, with
the images, drawings and charts embedded on separate slides and any text, arrows
or other symbols simply overlain on them using Powerpoint�s built-in drawing
tools, which are easy to use and quite suitable for this task. Any annotations
can be made using Powerpoint�s built-in notes feature. In this fashion, the
inbuilt resolution of the image can be retained (the publisher can copy and
paste the image readily into a photo editing package such as Photoshop) and the
resolution-independent text, arrows etc can be accurately positioned so the
publisher can see exactly what the author intended.
Ultimately the would-be author must supply the images in a
well-organised, appropriate quality fashion as requested by the publisher�s
instructions to authors.
Vector-Based Image Software
Although medical images are universally
resolution-dependent and pixel-based, virtually all charting and graphing
software produces resolution-independent images that are vector-based; i.e.,
the graphic file represents a series of instructions to draw graphic primitives
using precise mathematical descriptors rather than pixel by pixel descriptions
of an image. These images can be resized to any resolution desired prior to
final export and printing.
There are three major types of such software:
- Software designed to automatically create a wide range of charts and
graphs from data that has been entered into a table or database (e.g., Excel,
- Software designed to permit drawing a relatively limited range of
predetermined shapes and objects using graphic libraries to create diagrams
(e.g., Visio, Omnigraffle, Powerpoint)
- Software designed to draw virtually any shape or object using highly
sophisticated drawing tools (e.g., Adobe Illustrator, Corel Draw, Macromedia
Most users are familiar with the built-in charting tools
in Microsoft Office, which create usable business charts readily, but which
lack most of the tools needed to create sophisticated scientific charts and
graphs (e.g., box plots, whisker plots, automatically calculated error bars,
splines, regression lines, curves of best fit etc.). Each software programme
usually requires considerable effort to master, but if you create such charts
frequently this effort is well worthwhile.
For publication, a few simple rules for such charts should
be followed, namely:
- Always ask yourself what exactly you are trying to show with the chart.
This should ideally be with one or two clear unambiguous sentences. If some
data elements do not fit this explanation, they should probably be omitted from
- 2-dimensional charts are the rule; 3-dimensional charts are difficult to
read accurately and to obtain useful comparisons between datasets. �Pseudo-3D�
effects in particular are meaningless.
- All charts should be simple black and white line drawings for printing,
with minimal greyscale shading, patterning, series marking and other effects;
this should be kept only to what is absolutely necessary to show the
differences between datasets. Colour can be sparingly and effectively used for
onscreen presentations and web publication.
- Continuous data can be represented by a line connecting data points;
discontinuous data should either be presented as a scatter plot or as a
histogram or column chart
- Try to have no more than 6 datasets represented on a single chart -
having any more makes the chart very difficult to interpret; large numbers of
datasets can be represented either by aggregated data or a series of charts
representing subsets of the data
- Each chart should have a title, and each axis should be labelled clearly
including the units of measure and data categories as appropriate. A legend is
desirable if there are multiple datasets
- Keep gridlines, chart shading and text datapoints to a minimum
- Avoid duplicating the data in a chart in an accompanying table, unless
the chart is to show a very specific trend or feature of the data that is
difficult to extract from the table.
- Always preview and adjust the chart at the expected final size for
printing; it is surprising how often such �automatic� charting changes the
relationship and position of elements between different sizes and shapes of the
various elements of the chart (Excel is particularly prone to this)
Primitives, Freeforms & Beziers
People familiar with the Drawing environment of Microsoft
Office are familiar with the concept of drawing with predefined primitives such
as ovals, rectangles, polygons, arcs, lines and arrows. These greatly simplify
the process of drawing many simple diagrams, and with more sophisticated tools
such as Microsoft Visio or Omnigraffle, can create quite complex diagrams.
This type of software is quite useful for many
applications in teaching of Radiology, including process flow charts, clinical
decision algorithms, Venn diagrams, physics principles and so on (Figure 10). The
simple tools within Microsoft Office are quite limited, so any complex diagrams
probably require additional purchase and learning a further application.
Professional Drawing Applications
The software tools described above are not suited to
creating complex drawings of objects with numerous layers, photorealistic
rendering or extremely finely detailed graphics; such tasks require
professional level illustration software such as Adobe Illustrator, and are
again overkill for most Radiology illustrations for publication. In general, most
scientific users and radiologists will have little need for this software; the
complexity of learning and using these tools effectively is too rarely used and
is best left to graphics professionals.
These applications are sophisticated drawing environments
and allow for images of almost infinite size to be created at extremely high
levels of detail. They are ideal for creating structural drawings or graphics
using complex effects (Figures 11 and 12).
All modern computer operating systems have built-in
software for managing and viewing images stored in various folders in the
user�s document filing system. However, this built-in software is not very
useful for very large image collections, sophisticated searches, filing and
archiving. In particular such software is unable to handle DICOM images.
A software tool which will become indispensable after more
than a few dozen images are obtained is image database software (Figure 13). The
most ubiquitous is probably the Adobe Bridge programme, as it is bundled with
every copy of Photoshop and Photoshop Elements. Moreover, the latest Photoshop
CS3 Extended Edition directly supports cataloguing, opening and editing DICOM
image files without an intermediate conversion step.
There are several other powerful packages, which can
maintain separate fully linked and indexed databases of images (even on
external storage media) and which can also link between images of related type,
subject, place, date etc. according to various flexible keyword categories
assigned by the user. In addition, some applications also have powerful version
control, inbuilt RAW image editing and processing tools, can export and
repurpose images according to publication requirements as needed, and are
eminently suited to a professional collection of thousands of high resolution
images. Examples of such software applications include Adobe Lightroom, Apple
Aperture, and Microsoft Expression Media.
Images should in general be organised by organ system, by
pathology, by case and so on, and file naming and tagging should be performed
fairly regularly to ensure that as much information as possible is available
for future searches and utilisation.
The importance of backup of the images cannot be
overemphasised, as hard disks are intrinsically unsafe methods of long term
archival storage, being prone to sudden catastrophic hardware failure,
particularly as they age. There is little worse for a radiologist than to
realise the entire annotated carefully edited set of images of a particularly
rare irreplaceable case, or even an entire collection of cases, has been lost
forever due to hard drive failure.
Archival backup and storage of multiple copies of the
images on high quality optical media, preferably one or two sets representing
the original, untouched images, and one or two sets representing the edited,
annotated image sets and their storage heirarchies. Backup should be performed
regularly, ideally daily or at least weekly, with a regular systematic
There is more to creating good illustrations for
publication than meet the eye. The paramount consideration should be whether
the reader will find the illustrations informative and easily interpretable
without resorting to reading the text. If the images fail this simple test,
they are deficient and require additional thought, planning and redesign.
There is a plethora of software tools available that can
easily create elegant clear graphics and illustrations which readily explain a
scientific principle. Unfortunately this same software can be used just as
easily to create complex, unclear, poorly presented information which could
either obscure the main principles or confuse the reader. The difference lies
in the end user and his/her use of the software. The availability of such tools
does not remove the onus on the author to be clear, both in mind as to what the
illustration is meant to show, as well as how to best depict the relevant
And as always, it is crucial for the author(s) to
carefully read the instructions to authors, especially for print publications,
which tend to limit printing to black and white/greyscale and which often state
explicitly a limit to the number of illustrations and the specifics of image
size and resolution as well as file formats required. Deviation from these
guidelines may mean increased expense to the authors, or more commonly,
nonpublication of images and charts one has laboured hard to create.
- Virtually everything written by Edward R. Tufte.
(All at https://www.edwardtufte.com/tufte/index)
- E.R. Tufte. The Visual Display of Quantitative Information. 2nd
- Graphics and Web Design Based on Edward Tufte's Principles.
University of Washington School of Computing (http://www.washington.edu/computing/training/560/zz-tufte.html),
- Adobe Photoshop Elements Techniques. http://www.photoshopelementsuser.com/
- B. Brundage. Photoshop Elements 6: The Missing Manual, Pogue
- L.U. Fuller and D. McClelland. Photoshop CS3 Bible. Visual Press
- P. Wood. Scientific Illustration: A Guide to Biological, Zoological,
and Medical Rendering Techniques, Design, Printing, and Display. Wiley
- M. de la Flor. The Digital Biomedical Illustration Handbook. Charles
River Media (2004)
- E.S. Hodges (Ed.) The Guild Handbook of Scientific Illustration. Wiley
- Adobe Photoshop Elements 6 (www.adobe.com)
- Adobe Photoshop CS3 Extended Edition (www.adobe.com)
- Neat Image (noise reduction) (www.neatimage.com)
- LensFix & PanoTools (lens distortion correction) (www.kekus.com)
- Kaleidagraph (www.synergy.com)
- Deltagraph (www.rockware.com)
- Omnigraffle (www.omnigroup.com)
- Microsoft Office & Visio (www.microsoft.com/office/visio/)
Drawing & Illustration
- Adobe Illustrator (www.adobe.com)
Image Cataloguing, Organisation and Workflow
- Adobe Bridge (www.adobe.com)
- Microsoft Expression Media (www.microsoft.com/Expression/)
- Apple Aperture (www.apple.com)
- Adobe Lightroom (www.adobe.com)
Figure 1 Screenshot of Photoshop with Levels adjustment layer added and dialog opened for adjustment of image brightness and contrast as well as greyscale range.
Figure 10 A simple workflow diagram created using object-oriented drawing tools such as those found in Microsoft Office, Microsoft Visio or OmniGraffle.
Figure 11 Vector bezier-type drawing software (Macromedia FreeHand) showing the �wireframe� line depiction of a drawing of two taps, with all shading and colour rendering off.
Figure 12 1600% magnification view of a portion of the same drawing with shading and colour rendering on. Note the preservation of fine detail and precision in the image.
Figure 13 Screenshot of a typical image management software application showing multiple versions of images which can be organised heirarchically in folders as shown in the file browser on the left. The images can be sorted, renamed, even filed offline on external media, and opened with other applications for adjustment and editing.
Figure 2 Image preview after levels adjustment performed.
Figure 3 After cropping, creating a Fill Layer with a solid dark grey fill.
Figure 4 Fill layer edited roughly with the lasso tool to reveal most of the desired underlying image; this will be touched up with the brush tool.
Figure 5 Image after fill edge editing. Greasepoint pencil marks which were visible were removed using the healing brush tool.
Figure 6 The image is then resized and sharpened.
Figure 7 Text, arrows and stars are added using the Text tool; this creates a new layer for each text element which remains editable and repositionable at all times. This is saved as a Photoshop (.PSD) file with all layers intact.
Figure 8 Saving the image as a JPEG or single layer TIFF file collapses all the layers into a single flattened image for publication.
Figure 9 Examples of various charts created by scientific charting software.
|Received 18 December 2007; accepted 10 January 2008
Correspondence: Department of Diagnostic Radiology, Yong Loo Lin School of Medicine, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119075. Tel.: (65) 6772-4212; Fax: (65) 6773-0191; E-mail: email@example.com (Shih-Chang Wang).
Please cite as: Wang SC,
Preparing effective medical illustrations for publication (Part 2): software processing, drawing and illustration, Biomed Imaging Interv J 2008; 4(2):e12