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<HTML>
<HEAD>
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<TITLE>GNU Octave - Image Processing</TITLE>
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<P><HR><P>
<H1><A NAME="SEC163" HREF="octave_toc.html#TOC163">Image Processing</A></H1>
<P>
Octave can display images with the X Window System using the
<CODE>xloadimage</CODE> program. You do not need to be running X in order to
manipulate images, however, so some of these functions may be useful
even if you are not able to view the results.
</P>
<P>
Loading images only works with Octave's image format (a file with a
matrix containing the image data, and a matrix containing the
colormap). Contributions of robust, well-written functions to read
other image formats are welcome. If you can provide them, or would like
to improve Octave's image processing capabilities in other ways, please
contact @email{bug-octave@bevo.che.wisc.edu}.
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>colormap</B> <I>(<VAR>map</VAR>)</I>
<DD><A NAME="IDX814"></A>
<DT><U>Function File:</U> <B>colormap</B> <I>("default")</I>
<DD><A NAME="IDX815"></A>
Set the current colormap.
</P>
<P>
<CODE>colormap (<VAR>map</VAR>)</CODE> sets the current colormap to <VAR>map</VAR>. The
color map should be an <VAR>n</VAR> row by 3 column matrix. The columns
contain red, green, and blue intensities respectively. All entries
should be between 0 and 1 inclusive. The new colormap is returned.
</P>
<P>
<CODE>colormap ("default")</CODE> restores the default colormap (a gray scale
colormap with 64 entries). The default colormap is returned.
</P>
<P>
With no arguments, <CODE>colormap</CODE> returns the current color map.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>gray</B> <I>(<VAR>n</VAR>)</I>
<DD><A NAME="IDX816"></A>
Return a gray colormap with <VAR>n</VAR> entries corresponding to values from
0 to <VAR>n</VAR>. The argument <VAR>n</VAR> should be a scalar. If it is
omitted, 64 is assumed.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> [<VAR>img</VAR>, <VAR>map</VAR>] = <B>gray2ind</B> <I>(<VAR></VAR>)</I>
<DD><A NAME="IDX817"></A>
Convert a gray scale intensity image to an Octave indexed image.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>image</B> <I>(<VAR>x</VAR>, <VAR>zoom</VAR>)</I>
<DD><A NAME="IDX818"></A>
Display a matrix as a color image. The elements of <VAR>x</VAR> are indices
into the current colormap and should have values between 1 and the
length of the colormap. If <VAR>zoom</VAR> is omitted, a value of 4 is
assumed.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>imagesc</B> <I>(<VAR>x</VAR>, <VAR>zoom</VAR>)</I>
<DD><A NAME="IDX819"></A>
Display a scaled version of the matrix <VAR>x</VAR> as a color image. The
matrix is scaled so that its entries are indices into the current
colormap. The scaled matrix is returned. If <VAR>zoom</VAR> is omitted, a
value of 4 is assumed.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>imshow</B> <I>(<VAR>x</VAR>, <VAR>map</VAR>)</I>
<DD><A NAME="IDX820"></A>
<DT><U>Function File:</U> <B>imshow</B> <I>(<VAR>x</VAR>, <VAR>n</VAR>)</I>
<DD><A NAME="IDX821"></A>
<DT><U>Function File:</U> <B>imshow</B> <I>(<VAR>i</VAR>, <VAR>n</VAR>)</I>
<DD><A NAME="IDX822"></A>
<DT><U>Function File:</U> <B>imshow</B> <I>(<VAR>r</VAR>, <VAR>g</VAR>, <VAR>b</VAR>)</I>
<DD><A NAME="IDX823"></A>
Display images.
</P>
<P>
<CODE>imshow (<VAR>x</VAR>)</CODE> displays an indexed image using the current
colormap.
</P>
<P>
<CODE>imshow (<VAR>x</VAR>, <VAR>map</VAR>)</CODE> displays an indexed image using the
specified colormap.
</P>
<P>
<CODE>imshow (<VAR>i</VAR>, <VAR>n</VAR>)</CODE> displays a gray scale intensity image.
</P>
<P>
<CODE>imshow (<VAR>r</VAR>, <VAR>g</VAR>, <VAR>b</VAR>)</CODE> displays an RGB image.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>ind2gray</B> <I>(<VAR>x</VAR>, <VAR>map</VAR>)</I>
<DD><A NAME="IDX824"></A>
Convert an Octave indexed image to a gray scale intensity image.
If <VAR>map</VAR> is omitted, the current colormap is used to determine the
intensities.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> [<VAR>r</VAR>, <VAR>g</VAR>, <VAR>b</VAR>] = <B>ind2rgb</B> <I>(<VAR>x</VAR>, <VAR>map</VAR>)</I>
<DD><A NAME="IDX825"></A>
Convert an indexed image to red, green, and blue color components.
If <VAR>map</VAR> is omitted, the current colormap is used for the conversion.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> [<VAR>x</VAR>, <VAR>map</VAR>] = <B>loadimage</B> <I>(<VAR>file</VAR>)</I>
<DD><A NAME="IDX826"></A>
Load an image file and it's associated color map from the specified
<VAR>file</VAR>. The image must be stored in Octave's image format.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>rgb2ntsc</B> <I>(<VAR>rgb</VAR>)</I>
<DD><A NAME="IDX827"></A>
Image format conversion.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>ntsc2rgb</B> <I>(<VAR>yiq</VAR>)</I>
<DD><A NAME="IDX828"></A>
Image format conversion.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>ocean</B> <I>(<VAR>n</VAR>)</I>
<DD><A NAME="IDX829"></A>
Create color colormap. The argument <VAR>n</VAR> should be a scalar. If it
is omitted, 64 is assumed.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> [<VAR>x</VAR>, <VAR>map</VAR>] = <B>rgb2ind</B> <I>(<VAR>r</VAR>, <VAR>g</VAR>, <VAR>b</VAR>)</I>
<DD><A NAME="IDX830"></A>
Convert and RGB image to an Octave indexed image.
</DL>
</P>
<P>
<DL>
<DT><U>Function File:</U> <B>saveimage</B> <I>(<VAR>file</VAR>, <VAR>x</VAR>, <VAR>fmt</VAR>, <VAR>map</VAR>)</I>
<DD><A NAME="IDX831"></A>
Save the matrix <VAR>x</VAR> to <VAR>file</VAR> in image format <VAR>fmt</VAR>. Valid
values for <VAR>fmt</VAR> are
</P>
<DL COMPACT>
<DT><CODE>"img"</CODE>
<DD>
Octave's image format. The current colormap is also saved in the file.
<DT><CODE>"ppm"</CODE>
<DD>
Portable pixmap format.
<DT><CODE>"ps"</CODE>
<DD>
PostScript format. Note that images saved in PostScript format can not
be read back into Octave with loadimage.
</DL>
<P>
If the fourth argument is supplied, the specified colormap will also be
saved along with the image.
</P>
<P>
Note: if the colormap contains only two entries and these entries are
black and white, the bitmap ppm and PostScript formats are used. If the
image is a gray scale image (the entries within each row of the colormap
are equal) the gray scale ppm and PostScript image formats are used,
otherwise the full color formats are used.
</DL>
</P>
<P>
<DL>
<DT><U>Built-in Variable:</U> <B>IMAGEPATH</B>
<DD><A NAME="IDX832"></A>
A colon separated list of directories in which to search for image
files.
</DL>
</P>
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