Next: Displaying Images, Up: Image Processing [Contents][Index]
32.1 Loading and Saving Images
- 32.2 Displaying Images. A natural part of image processing is visualization of an image. The most basic function for this is the imshow function that shows the image given in the first input argument.: imshow (im): imshow (im, limits): imshow (im, map): imshow (rgb, ): imshow (filename): imshow (, stringparam1, value1, ): h = imshow Display the image im, where im can be a 2.
- Photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc. GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything. GNU Image Manipulation Program a.
The first step in most image processing tasks is to load an imageinto Octave which is done with the
imread
function.The imwrite
function is the corresponding functionfor writing images to the disk.In summary, most image processing code will follow the structure of this code
Octave image processing toolbox free download. Octave Forge Octave Forge is a central location for collaborative development of packages for GNU Octave. The Octave-forge Image package provides functions for processing images. The package also provides functions for feature extraction, image statistics, spatial and geometric transformations, morphological operations, linear filtering, and much more.
Read images from various file formats.
Read an image as a matrix from the file filename or from the onlineresource url. If neither is given, but ext was specified, lookfor a file with the extension ext.
The size and class of the output depends on the format of the image. Acolor image is returned as an MxNx3 matrix. Grayscale andblack-and-white images are of size MxN. Multipage images willhave an additional 4th dimension.
The bit depth of the image determines the class of the output:
'uint8'
, 'uint16'
, or 'single'
for grayscale andcolor, and 'logical'
for black-and-white. Note that indexed imagesalways return the indexes for a colormap, independent of whether mapis a requested output. To obtain the actual RGB image, use ind2rgb
.When more than one indexed image is being read, map is obtained fromthe first. In some rare cases this may be incorrect and imfinfo
canbe used to obtain the colormap of each image.See the Octave manual for more information in representing images.
Some file formats, such as TIFF and GIF, are able to store multiple imagesin a single file. idx can be a scalar or vector specifying theindex of the images to read. By default, Octave will read only the firstpage.
Depending on the file format, it is possible to configure the reading ofimages with parameter, value pairs. The following options aresupported:
'Frames'
or 'Index'
This is an alternative method to specify idx. When specifying itin this way, its value can also be the string
'all'
.'Info'
This option exists for MATLAB compatibility, but has no effect. Formaximum performance when reading multiple images from a single file, usethe
'Index'
option.'PixelRegion'
Controls the image region that is read. The value must be a cell array withtwo arrays of 3 elements
{[rows], [cols]}
. Theelements in the array are the start, increment, and end pixel to be read.If the increment value is omitted it defaults to 1. For example, thefollowing are all equivalent:See also:imwrite, imfinfo, imformats.
Write images in various file formats.
The image img can be a binary, grayscale, RGB, or multi-dimensionalimage. The size and class of img should be the same as what shouldbe expected when reading it with
imread
: the 3rd and 4th dimensionsreserved for color space, and multiple pages respectively. If it’s anindexed image, the colormap map must also be specified.If ext is not supplied, the file extension of filename is usedto determine the format. The actual supported formats are dependent onoptions made during the build of Octave. Use
imformats
to checkthe support of the different image formats.Depending on the file format, it is possible to configure the writing ofimages with param, val pairs. The following options aresupported:
Alpha (transparency) channel for the image. This must be a matrix withsame class, and number of rows and columns of img. In case of amultipage image, the size of the 4th dimension must also match and the thirddimension must be a singleton. By default, image will be completely opaque.
Compression to use one the image. Can be one of the following: 'none'(default), 'bzip', 'fax3', 'fax4', 'jpeg', 'lzw', 'rle', or 'deflate'.Note that not all compression types are available for all image formatsin which it defaults to your Magick library.
For formats that accept animations (such as GIF), controls for how long aframe is displayed until it moves to the next one. The value must be scalar(which will applied to all frames in img), or a vector of lengthequal to the number of frames in im. The value is in seconds, mustbe between 0 and 655.35, and defaults to 0.5.
![Gnu Gnu](https://www.researchgate.net/profile/Giuseppe-Montesanto/publication/280829017/figure/fig6/AS:284501503692817@1444841852641/GNU-Image-Manipulation-Program-A-Portion-of-the-Export-Image-window-showing-the_Q320.jpg)
For formats that accept animations (such as GIF), controls what happens toa frame before drawing the next one. Its value can be one of thefollowing strings: 'doNotSpecify' (default); 'leaveInPlace'; 'restoreBG';and 'restorePrevious', or a cell array of those string with length equalto the number of frames in img.
For formats that accept animations (such as GIF), controls how many timesthe sequence is repeated. A value of Inf means an infinite loop (default),a value of 0 or 1 that the sequence is played only once (loops zero times),while a value of 2 or above loops that number of times (looping twice meansit plays the complete sequence 3 times). This option is ignored when thereis only a single image at the end of writing the file.
Set the quality of the compression. The value should be an integerbetween 0 and 100, with larger values indicating higher visual quality andlower compression. Defaults to 75.
Some file formats, such as TIFF and GIF, are able to store multiple imagesin a single file. This option specifies if img should be appendedto the file (if it exists) or if a new file should be created for it(possibly overwriting an existing file). The value should be the string
'Overwrite'
(default), or 'Append'
.Despite this option, the most efficient method of writing a multipageimage is to pass a 4 dimensional img to
imwrite
, the samematrix that could be expected when using imread
with the option'Index'
set to 'all'
.See also:imread, imfinfo, imformats.
Query or set the internal variable that specifies a colon separatedlist of directories in which to search for image files.
When called from inside a function with the
'local'
option, thevariable is changed locally for the function and any subroutines it calls.The original variable value is restored when exiting the function.See also:EXEC_PATH, OCTAVE_HOME, OCTAVE_EXEC_HOME.
It is possible to get information about an image file on disk, without actuallyreading it into Octave. This is done using the
imfinfo
function whichprovides read access to many of the parameters stored in the header of theimage file.Read image information from a file.
imfinfo
returns a structure containing information about the imagestored in the file filename. If there is no file filename,and ext was specified, it will look for a file named filenameand extension ext, i.e., a file named filename.ext.The output structure info contains the following fields:
The full name of the image file.
Date of last modification to the file.
Number of bytes of the image on disk
Image format (e.g.,
'jpeg'
).Image height in pixels.
Image Width in pixels.
Number of bits per channel per pixel.
Image type. Value is
'grayscale'
, 'indexed'
,'truecolor'
, 'CMYK'
, or 'undefined'
.X resolution of the image.
Y resolution of the image.
Units of image resolution. Value is
'Inch'
,'Centimeter'
, or 'undefined'
.Time in 1/100ths of a second (0 to 65535) which must expire beforedisplaying the next image in an animated sequence.
Number of iterations to loop an animation.
Endian option for formats that support it. Value is
'little-endian'
, 'big-endian'
, or 'undefined'
.![Gnu Image Processing Gnu Image Processing](https://solarianprogrammer.com/images/2019/07/11/image_processing.png)
Gamma level of the image. The same color image displayed on two differentworkstations may look different due to differences in the display monitor.
JPEG/MIFF/PNG compression level. Value is an integer in the range [0 100].
Only valid for GIF images, control how successive frames are rendered (howthe preceding frame is disposed of) when creating a GIF animation. Valuescan be
'doNotSpecify'
, 'leaveInPlace'
, 'restoreBG'
,or 'restorePrevious'
. For non-GIF files, value is an empty string.Value is a 1x8 Matrix with the x,y chromaticity values for white, red,green, and blue points, in that order.
Image comment.
Compression type. Value can be
'none'
, 'bzip'
,'fax3'
, 'fax4'
, 'jpeg'
, 'lzw'
,'rle'
, 'deflate'
, 'lzma'
, 'jpeg2000'
,'jbig2'
, 'jbig2'
, or 'undefined'
.Colormap for each image.
The orientation of the image with respect to the rows and columns. Valueis an integer between 1 and 8 as defined in the TIFF 6 specifications, andfor MATLAB compatibility.
Name and version of the software or firmware of the camera or image inputdevice used to generate the image.
The manufacturer of the recording equipment. This is the manufacture of theDSC, scanner, video digitizer or other equipment that generatedthe image.
The model name or model number of the recording equipment as mentioned onthe field
'Make'
.The date and time of image creation as defined by the Exif standard, i.e.,it is the date and time the file was changed.
The title of the image as defined by the Exif standard.
Name of the camera owner, photographer or image creator.
Copyright notice of the person or organization claiming rights to the image.
A struct with information retrieved from the Exif tag.
A struct with geotagging information retrieved from the Exif tag.
See also:imread, imwrite, imshow, imformats.
By default, Octave’s image IO functions (
imread
, imwrite
,and imfinfo
) use the GraphicsMagick
library for theiroperations. This means a vast number of image formats is supportedbut considering the large amount of image formats in science andits commonly closed nature, it is impossible to have a librarycapable of reading them all. Because of this, the functionimformats
keeps a configurable list of available formats,their extensions, and what functions should the image IO functionsuse. This allows one to expand Octave’s image IO capabilities bycreating functions aimed at acting on specific file formats.While it would be possible to call the extra functions directly,properly configuring Octave with
imformats
allows one to keep aconsistent code that is abstracted from file formats.It is important to note that a file format is not actually defined by itsfile extension and that
GraphicsMagick
is capable to read and writemore file formats than the ones listed by imformats
. What thismeans is that even with an incorrect or missing extension the image maystill be read correctly, and that even unlisted formats are not necessarilyunsupported.Manage supported image formats.
formats is a structure with information about each supported fileformat, or from a specific format ext, the value displayed on thefield ext. It contains the following fields:
The name of the file format. This may match the file extension but Octavewill automatically detect the file format.
A long description of the file format.
A function handle to confirm if a file is of the specified format.
A function handle to write if a file is of the specified format.
A function handle to open files the specified format.
A function handle to obtain image information of the specified format.
Logical value if format supports alpha channel (transparency or matte).
Logical value if format supports multipage (multiple images per file).
It is possible to change the way Octave manages file formats with theoptions
'add'
, 'remove'
, and 'update'
, and supplyinga structure format Can t open zip folder. with the required fields. The option'factory'
resets the configuration to the default.This can be used by Octave packages to extend the image reading capabilitiesOctave, through use of the PKG_ADD and PKG_DEL commands.
See also:imfinfo, imread, imwrite.
Next: Displaying Images, Up: Image Processing [Contents][Index]
Next: Representing Images, Previous: Loading and Saving Images, Up: Image Processing [Contents][Index]
32.2 Displaying Images
A natural part of image processing is visualization of an image.The most basic function for this is the
imshow
function thatshows the image given in the first input argument.Display the image im, where im can be a 2-dimensional(grayscale image) or a 3-dimensional (RGB image) matrix.
If limits is a 2-element vector
[low, high]
, theimage is shown using a display range between low and high. Ifan empty matrix is passed for limits, the display range is computedas the range between the minimal and the maximal value in the image.If map is a valid color map, the image will be shown as an indexedimage using the supplied color map.
If a filename is given instead of an image, the file will be read and shown.
If given, the parameter string_param1 has value value1.string_param1 can be any of the following:
'displayrange'
value1 is the display range as described above.
Gnu Image Manipulation Software
'colormap'
value1 is the colormap to use when displaying an indexed image.
'xdata'
Gnu Image Download
If value1 is a two element vector, it must contain horizontal axislimits in the form [xmin xmax]; Otherwise value1 must be a vector andonly the first and last elements will be used for xmin and xmaxrespectively.
'ydata'
If value1 is a two element vector, it must contain vertical axislimits in the form [ymin ymax]; Otherwise value1 must be a vector andonly the first and last elements will be used for ymin and ymaxrespectively.
The optional return value h is a graphics handle to the image.
See also:image, imagesc, colormap, gray2ind, rgb2ind.
Display a matrix as an indexed color image.
The elements of img are indices into the current colormap.
x and y are optional 2-element vectors,
[min, max]
,which specify the range for the axis labels. If a range is specified as[max, min]
then the image will be reversed along that axis. Forconvenience, x and y may be specified as N-element vectorsmatching the length of the data in img. However, only the first andlast elements will be used to determine the axis limits.Multiple property/value pairs may be specified for the image object, butthey must appear in pairs.
The optional return value h is a graphics handle to the image.
Implementation Note: The origin (0, 0) for images is located in theupper left. For ordinary plots, the origin is located in the lowerleft. Octave handles this inversion by plotting the data normally,and then reversing the direction of the y-axis by setting the
ydir
property to 'reverse'
. This has implications wheneveran image and an ordinary plot need to be overlaid. The recommendedsolution is to display the image and then plot the reversed ydatausing, for example, flipud (ydata)
.Calling Forms: The
image
function can be called in two forms:High-Level and Low-Level. When invoked with normal options, the High-Levelform is used which first calls newplot
to prepare the graphic figureand axes. When the only inputs to image
are property/value pairsthe Low-Level form is used which creates a new instance of an image objectand inserts it in the current axes.See also:imshow, imagesc, colormap.
Display a scaled version of the matrix img as a color image.
The colormap is scaled so that the entries of the matrix occupy the entirecolormap. If
climits = [lo, hi]
is given, thenthat range is set to the 'clim'
of the current axes.The axis values corresponding to the matrix elements are specified inx and y, either as pairs giving the minimum and maximumvalues for the respective axes, or as values for each row and columnof the matrix img.
The optional return value h is a graphics handle to the image.
Calling Forms: The
imagesc
function can be called in two forms:High-Level and Low-Level. When invoked with normal options, the High-Levelform is used which first calls newplot
to prepare the graphic figureand axes. When the only inputs to image
are property/value pairsthe Low-Level form is used which creates a new instance of an image objectand inserts it in the current axes.See also:image, imshow, caxis.
Next: Representing Images, Previous: Loading and Saving Images, Up: Image Processing [Contents][Index]