SaveAsEps converts a grayscale image (in a Matlab matrix) to a
PostScript file that a LaserWriter or Linotype will accurately render on
paper. The output file is a standard Encapsulated PostScript File, with
file type ‘EPSF’, commonly referred to as an “eps” file. Most word
processors, e.g. Word and PageMaker, know how to import eps files.
Macintoshes only understand QuickDraw, not PostScript, so they don’t
know what image the PostScript code would produce. The Macintosh file
“creator” of the eps file is set to Microsoft Word, so double-clicking
it will open it as a Word document containg the image.
I suggest you use the $25 shareware Macintosh application EPS Factory
to add a PICT preview to your file, based on the postscript already
there. You can download EPS Factory from
(The old freeware ps2eps is incompatible with Mac OS 8.6 and 9, alas.)
The PICT preview will make the image will look approximately right on
your monitor, e.g. in Word.
If you want to convert the EPS file to some other format, we recommend
using Adobe Illustrator, especially the “Export to Web” feature.
To import into Word, use the Insert:Picture or
Insert:File command. Once imported, you can get Word to rescale the
image by dragging the image’s lower right corner while holding down the
shift key. Try the VideoToolbox demo Grating. Bear in mind that
on-screen you’re looking at the PICT, whereas, when you print on a
LaserWriter, the image is produced by the PostScript code. When in your
word processor, the on-screen images will look best if you use the
Monitors control panel to set your monitor to 256 Grays, but this won’t
The filename, by convention, should end in ‘.eps’ to indicate that it’s
an encapsulated postscript file, but this is not enforced. The file’s
type is set to ‘EPSF’ with creator ‘R*ch’. (This creator corresponds to
BBEdit, so double-clicking will open it as a text file in BBEdit, which
includes a Special:SendPostScript command for downloading poscript
images to the laserwriter. You can change the creator to be anything you
The image matrix must have 8 bits per pixel (i.e. values 0 to 255). No color tables are used. The raw pixel value (Apple calls it an "index") is sent directly to the printer with no transformation. [PostScript](PostScript) assumes that the number, from 0 to 255 is proportional to desired reflectance, from zero to 1. The pageRect is subtle. It describes, in typographers points (1/72"), the rectangle that your image will be mapped onto on the printed page. It is essential that you keep in mind that Apple and Adobe use different coordinate systems. Both Apple and Adobe increase x from left to right. However, Apple has y increasing from top to bottom, whereas Adobe increases y from bottom to top. Adobe's origin is the lower left corner of the page, even though that point is usually not printable, since most printers can only print to within about a half inch of the edge. The pageRect, though supplied in Apple's Rect data structure, must be in Adobe's coordinates, respecting the names of the Rect structure's fields: left, top, right, bottom. So, for an image to fill most of an 8.5x11 page, with 0.5" margins, you might use the following: pageRect=[SetRect](SetRect)(0.5,10.5,8,0.5)\*72;
In printing PostScript halftones the halftone cell size determines both
the spatial and graylevel resolutions of the resulting image. If the
“resolution” parameter is positive, then it specifies the cellsPerInch;
if it’s negative then it specifies the number of grayLevels. If
“resolution” is omitted then the printer will be left at its default
cell size, which is usually a good choice. Note that there need not be
any particular correspondence between pixels in your image and cells in
the halftone; the printer automatically resamples your image to produce
If you specify cellsPerInch (resolution>0) then the printer will be
asked to print its halftone with that many halftone cells per inch. E.g.
to produce a halftone original for subsequent one-to-one reproduction in
a journal, you’ll want the cells to be coarse enough for them to
reproduce without re-screening, e.g. 100 cells per inch.
Alternatively, if you specify grayLevels (resolution<0) then the printer
will be asked to print its halftone with cells containing grayLevels-1
printer pixels, yielding the specified number of gray levels. E.g. you
might want to force your 300 dpi LaserWriter to use big cells yielding
256 gray levels.
If resolution==0 or resolution==, it will be ignored.
Here’s a minimal example that prints an image to disk, preserving the
size and scale of the image,
The default pageRect is equivalent to this:
pageRect=[SetRect](SetRect)(0,-0,size(m,2),-size(m,1));% Adobe coordinates pageRect=[CenterRect](CenterRect)(pageRect,[SetRect](SetRect)(0,11,8.5,0)\*72); [SaveAsEps](SaveAsEps)('test.eps',m,pageRect);
Tiling is something we often want to do, creating a huge image by taping
many pages together. You accomplish this by repeatedly printing the huge
image–only one pageful appears each time–shifting the image so that
eventually every bit has been printed. (It’s slow, since the whole image
is transmitted to the printer each time.) Here’s an example that creates
a big “width” by “height” image. We tile onto multiple 8.5”x11” pages,
using 7.5”x10” of each page, allowing for 0.5” nonprinting margins:
delete 'test.eps'; mosaicRect=[SetRect](SetRect)(0,height,width,0); % In units of "points". 72 points/inch. mosaicRect=[OffsetRect](OffsetRect)(mosaicRect,0.5\*72,0.5\*72); % allow for nonprinting margin for i=0:7.5\*72:width for j=0:10\*72:height pageRect=mosaicRect; [OffsetRect](OffsetRect)(&pageRect,-i,-j); [ImageToPs](ImageToPs)('test.ps',m,pageRect); end end
In case your PostScript manual isn’t handy, the easy way to obtain
multiple copies of each page is to use the #copies variable that’s built
into Postscript. Anywhere in your file before “showpage”, set #copies to
the desired value: ‘/#copies 3 def\n’
There are many free PostScript downloaders, but I find them clumsy to
use, especially the ones that don’t inform you of errors, should they
occur. I like these:
BBEdit (used to come with an extension for downloading postscript)
(Don’t know if this is still available.)
LaserStatus, a desk accessory included in the
MockPackage Plus Utilities
1854 Fuller Road
PO Box 65580
West Des Moines, Iowa 50265
You may also want to read:
Adobe Systems (1985) PostScript Language Reference Manual, Second
Edition. Reading, MA: Addison-Wesley.
Pelli, D. G. (1987) Programming in PostScript: Imaging on paper from a
mathematical description. BYTE, 12 (5), 185-202.
The “resolution” parameter is ignored by my Apple LaserWriter 16/600.
I’ve looked at the PostScript code in the .eps file and it looks
perfect. For reasons that I don’t understand, the printer is ignoring
the setscreen command, leaving you at the default printer resolution.