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Image file formats & working guide lines



 

Contents
 

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Short notes about commonly used graphic programs

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Programs that work with pixels

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Programs that work with vectors

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File Formats

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Exporting images

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Presentations using Powerpoint

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Publications

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Posters

 

 


 

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Short notes about commonly used graphic programs

Regardless if the document to be presented is a manuscript, a poster or a Powerpoint presentation it's very important to know the difference between vector graphics and bitmapped or pixel graphics. E.g. it's very common that figures are made in Adobe Photoshop and imported to MS Word, even though the figure is a plot rather than e.g. a pure MR image without any annotation.
 

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Programs that work with pixels only include
* Adobe Photoshop (Mac, Windows)
* The GIMP (Linux)

They do import e.g. vectorized EPS images, but rasterizes them to pixels.
Never use these to make figures!

 

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Programs that work with vector graphics include
* Adobe Illustrator or Corel Draw (Mac, Windows)
Highly recommended for making figures. Adobe Illustrator can load, edit and save in PDF and EPS format. Additionally, it can export in virtually all vector and pixel based image formats.

* MS Powerpoint/Word (Mac, Windows)
Simple for beginners. Imports EPS and TIFF. Can save in PDF or EPS but the handling of objects in the drawing is not as reliable as in Illustrator.
 

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File formats

The following image format chart should be sufficient for all kinds of presentations
 

24-bits graphics = 16 million colours

16-bits graphics = 65 thousand colours

8-bit graphics = 256 colours
 

Image format

Format type

Use

Don't use

JPEG

Pixels, 24-bit

For MR-images, scanned photos, digital camera photos.

Presentation of these image types on the Web or in Powerpoint
Colour or gray scale.

Use JPEG quality about 90%

For figures in a manuscript/poster. Use TIFF instead if it's purely pixel graphics without letters or lines.

On the web, when the image contains thin lines, to avoid "Gibbs artefacts" around the lines.
 

Don't save the same file in JPEG format more than once, since JPEG uses lossy compression. During the editing process, save as TIFF.

NOTE! Everytime you save, close and re-open, your image is of less quality !

GIF

Pixels, 8-bit

As with JPEG, but with the disadvantage that it only supports 256 colours. This reduces the image quality a lot for colour images. Does not matter for gray scale images.

On the Web: Use GIF instead of JPEG for images that originally was vector based containing lines and letters.

For figures in a manuscript/poster. Use TIFF instead if it's purely pixel graphics without letters or lines.

TIFF

Pixels, 24-bit

For MR/PET-images or photos to be imported in Word, Powerpoint, Illustrator.
The press industry standard.

On the web, since TIFF-images aren't readable by Internet browsers.

For figures (including lines & letters etc.) in a manuscript/poster. If you want to use a TIFF MR-image in a figure, import the TIFF file in Illustrator (recommended) or Word and write the figure annotation in there.

EMF
Enhanced Media File (Windows)

Pixel & vector graphics

Format for Copy & Paste in Windows (CTRL-C/V)

If you want to use the figure in Powerpoint. This format is better than EPS for vector graphics if used in a Powerpoint presentation.

For electronic submission of figures to a journal/printing office, use EPS or PDF instead

EPS, PS

(Encapsulated Postscript)

Vector graphics, may embed pixel graphics

For figures. EPS & PS files can be created by printing (sometimes also by saving as..) to a Postcript File (install this printer driver) from all programs supporting printing.

They are editable in Illustrator and is the optimal format for submitting your figures electronically to journal/press.

IMPORTANT NOTES:
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From Matlab Figure menu: Export as... "EPS Color File", not "EPS Level 2 Color File". Otherwise it may not be read by Illustrator

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From Illustrator: Save as...EPS Version 6.0 . Choosing lower version results in no embedding of pixelbased images, while higher version number are not importable in MS Office 97 (2k/XP?)

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EPS/PS is the only format that can be directly copied to a Postscript printer from UNIX/Linux using the command 'lp' or 'lpr'.
Don't try e.g. 'lp file.tiff'

Don't import EPS-files in Powerpoint for slide show purposes. Use EMF instead. However, if you will print your Powerpoint document as a PDF file or to a Postscript printer you may well use the EPS-format.

PDF

Text, vector graphics, with embedded pixel graphics with many compression option

When your document is ready for sharing with others or for publication. This is the only format that is platform independent. Fonts are usually embedded to assure that the document looks the same on any screen and on any printer.

If you have Adobe Acrobat, you can print from any document to a PDF file. From Illustrator you can Save as..PDF.

This is usually the format for a printing office.


Your document may be protected for editing and/or printing.

Until your document (perhaps incl. figures) is complete. This is not a format useful for editing

PSD

Pixels, any-bit, multilayer

Native Photoshop format

In the (unlikely) case that you need several layers, you must also save your image in PSD format. Otherwise always save your images as TIFF.

For figures. Don't write figure annotation such as letters, arrow or numbers.

AI

Vector graphics
Native Illustrator format

If you are working in Illustrator. always save in Illustrators own format to assure that nothing changes when opening the document again. Save a copy in EPS or PDF format when done.




 

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Exporting images from your favorite analysis program (e.g. Matlab) into a presentation format without any loss of quality
A common scenario is to use a (modified) Matlab figure in Word (for manuscripts), Powerpoint (for presentations), Illustrator (for posters) or on the Web. Instead of Matlab you may have another program like e.g. Statistica.

Under all cicumstances don't use screen dumps and don't use a pixel program like Adobe Photoshop. If you need to modify the brightness or contrast of e.g. an MR image in a Matlab figure, do this by defining a intensity range as a second argument to imagesc(). If you work with e.g. SPM under Matlab or are using another analysis program, do the following:
* SPM: Press print. This creates/add pages to spmXX.ps
* Open the Postscript file in Adobe Illustrator, choose page if the ps-file contains multiple pages.
* Mark the actual MR image in the document and copy & paste into Photoshop.
* Adjust brightness/contrast in Photoshop, save as TIFF file, and import in the Illustrator program again.     
* Save the edited Matlab figure as AI, EPS version 6.0 (for Word), EMF (for Powerpoint slideshows)  and PDF.
 

 
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Presentations using Powerpoint
Export:
Vector graphics in Illustrator: Export... as EMF
Pixel graphics in e.g. Photoshop: Save as...TIFF (or JPEG). Avoid GIF if not gray scale
You may also use copy & paste from any program.

Import into Powerpoint:
Avoid importing EPS files into Powerpoint, unless your primary goal is to print the document out on a postscript printer of as a PDF file.
EPS files look naggy in a slide show.

 
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Publications
MS Word / Adobe InDesign:
In most cases you aren't supposed to import images in your manuscipt to a journal, but rather provide them as separate EPS files. But for e.g. a PhD Thesis you need to do the layout yourself. Then...
Import plain MR-images/photos as TIFF
Import ready figures in EPS Color format (remember to save as EPS version 6.0 in Illustrator so that MS Word can read them)


When your Word document is ready, print as PDF, so that the layout is guaranteed to be intact.


 

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Creating posters
Same as for publications.
However, if you will let a poster office print out your poster in one piece, use only Illustator and send them your document in Illustrator format and/or PDF.
PhD Thesis HINT! Often you and the printing office doesn't have the same fonts. If they want it in EPS format, do the following:
* Mark all (CTRL-A)
* Menu "Text"->Create Text Contours
* Save as... "<filename> contours.eps"  (NOTE ! Save a copy, don't overwrite)
Now you have only vector objects and no characters. Send them both versions, and maybe the PDF-version as well.

Budget solution: If you have Adobe InDesign, you can import an EPS file and print to a conventional A4/A3 printer using it's overlapping technique. Then you can cut & paste them together (using scissors and tape), forming a single sheet.