在Octave中加載圖像并轉成灰度圖時，發現rgb2gray()函數不存在，上網搜了一下，stackoverflow上給出了相關解釋，如下：

The problem is that you didn't load your packages. When you type pkg list you can find which ones are loaded by an asterisk in front of their names. Load a package with pkg load image.

Having to load a packages is that thing that most users find strange but if you compare with other languages, such as Python, Perl, or C++, would you expect them to import, use, or #include every libraries available in the system by default? See Octave's FAQ for more details.

原來Octave缺省狀態下缺少相關包，比如圖像處理、信號處理方面的包，需要我們手動安裝。

去sourceforge上下載相關包，放在Octave的搜索路徑上，在Octave的命令行中執行安裝命令：

pkg install -forge package_name

rgb2gray()函數需要安裝image包。

附一下sourceforge上Octave的相關包：

Packages

These packages are meant for current versions of Octave. See the unmaintainedsection for information on older versions.

bim

Package for solving Diffusion Advection Reaction (DAR) Partial Differential Equations

detailsdownload

bsltl

The BSLTL package is a free collection of OCTAVE/MATLAB routines for working with the biospeckle laser technique

detailsdownload

cgi

Common Gatway Interface for Octave

detailsdownload

communications

Digital Communications, Error Correcting Codes (Channel Code), Source Code functions, Modulation and Galois Fields

detailsdownload

control

Computer-Aided Control System Design (CACSD) Tools for GNU Octave, based on the proven SLICOT Library

detailsdownload

data-smoothing

Algorithms for smoothing noisy data

detailsdownload

database

Interface to SQL databases, currently only postgresql using libpq

detailsdownload

dataframe

Data manipulation toolbox similar to R data

detailsdownload

dicom

Digital communications in medicine (DICOM) file io

detailsdownload

divand

divand performs an n-dimensional variational analysis (interpolation) of arbitrarily located observations

detailsdownload

doctest

The Octave-Forge Doctest package finds specially-formatted blocks of example code within documentation files

detailsdownload

econometrics

Econometrics functions including MLE and GMM based techniques

detailsdownload

fem-fenics

pkg for the resolution of partial differential equations based on fenics

detailsdownload

financial

Monte Carlo simulation, options pricing routines, financial manipulation, plotting functions and additional date manipulation tools

detailsdownload

fits

The Octave-FITS package provides functions for reading, and writing FITS (Flexible Image Transport System) files

detailsdownload

fl-core

The package contains code for basic functions in Fuzzy Logic for Octave

detailsdownload

fpl

Collection of routines to export data produced by Finite Elements or Finite Volume Simulations in formats used by some visualization programs

detailsdownload

fuzzy-logic-toolkit

A mostly MATLAB-compatible fuzzy logic toolkit for Octave

detailsdownload

ga

Genetic optimization code

detailsdownload

general

General tools for Octave

detailsdownload

generate_html

This package provides functions for generating HTML pages that contain the help texts for a set of functions

detailsdownload

geometry

Library for geometric computing extending MatGeom functions

detailsdownload

image

The Octave-forge Image package provides functions for processing images

detailsdownload

image-acquisition

The Octave-forge Image Aquisition package provides functions to capture images from connected devices

detailsdownload

instrument-control

Low level I/O functions for serial, i2c, parallel, tcp, gpib, vxi11 and usbtmc interfaces

detailsdownload

interval

The interval package for real-valued interval arithmetic allows one to evaluate functions over subsets of their domain

detailsdownload

io

Input/Output in external formats.

detailsdownload

java

Provides Java interface with OO-like Java objects manipulation

detailsdownload

level-set

Routines for calculating the time-evolution of the level-set equation and extracting geometric information from the level-set function

detailsdownload

linear-algebra

Additional linear algebra code, including general SVD and matrix functions

detailsdownload

lssa

A package implementing tools to compute spectral decompositions of irregularly-spaced time series

detailsdownload

ltfat

The Large Time/Frequency Analysis Toolbox (LTFAT) is a Matlab/Octave toolbox for working with time-frequency analysis, wavelets and signal processing

detailsdownload

mapping

Simple mapping and GIS .shp and raster file functions

detailsdownload

mechanics

Library with functions useful for numerical computation in classical mechanics and structural analysis

detailsdownload

miscellaneous

Miscellaneous tools that don't fit somewhere else

detailsdownload

mpi

Octave bindings for basic Message Passing Interface (MPI) functions for parallel computing

detailsdownload

msh

Create and manage triangular and tetrahedral meshes for Finite Element or Finite Volume PDE solvers

detailsdownload

mvn

Multivariate normal distribution clustering and utility functions

detailsdownload

nan

A statistics and machine learning toolbox for data with and w/o missing values

detailsdownload

ncarray

Access a single or a collection of NetCDF files as a multi-dimensional array

detailsdownload

netcdf

A MATLAB compatible NetCDF interface for Octave

detailsdownload

nurbs

Collection of routines for the creation, and manipulation of Non-Uniform Rational B-Splines (NURBS), based on the NURBS toolbox by Mark Spink

detailsdownload

ocs

Package for solving DC and transient electrical circuit equations

detailsdownload

octcdf

A NetCDF interface for octave

detailsdownload

octclip

This package allows to do boolean operations with polygons using the Greiner-Hormann algorithm

detailsdownload

octproj

This package allows to call functions of PROJ

detailsdownload

odepkg

A package for solving ordinary differential equations and more

detailsdownload

optics

Functions covering various aspects of optics

detailsdownload

optim

Non-linear optimization toolkit

detailsdownload

optiminterp

An optimal interpolation toolbox for octave

detailsdownload

parallel

Parallel execution package

detailsdownload

quaternion

Quaternion package for GNU Octave, includes a quaternion class with overloaded operators

detailsdownload

queueing

The queueing package provides functions for queueing networks and Markov chains analysis

detailsdownload

secs1d

A Drift-Diffusion simulator for 1d semiconductor devices

detailsdownload

secs2d

A Drift-Diffusion simulator for 2d semiconductor devices

detailsdownload

secs3d

A Drift-Diffusion simulator for 3d semiconductor devices

detailsdownload

signal

Signal processing tools, including filtering, windowing and display functions

detailsdownload

sockets

Socket functions for networking from within octave

detailsdownload

sparsersb

Interface to the librsb package implementing the RSB sparse matrix format

detailsdownload

specfun

Special functions including ellipitic functions, etc

detailsdownload

splines

Additional spline functions

detailsdownload

statistics

Additional statistics functions for Octave

detailsdownload

stk

The STK is a (not so) Small Toolbox for Kriging

detailsdownload

strings

Additional functions for manipulation and analysis of strings

detailsdownload

struct

Additional Structure manipulations functions

detailsdownload

symbolic

The Octave-Forge Symbolic package adds symbolic calculation features to GNU Octave

detailsdownload

tisean

Port of TISEAN 3

detailsdownload

tsa

Stochastic concepts and maximum entropy methods for time series analysis

detailsdownload

video

A wrapper for ffmpeg's libavformat and libavcodec, implementing addframe, avifile, aviinfo and aviread

detailsdownload

vrml

3D graphics using VRML

detailsdownload

windows

Provides COM interface and additional functionality on Windows

detailsdownload

zeromq

ZeroMQ bindings for GNU Octave

detailsdownload

Renamed or moved packages

Some packages have been renamed or merged over time. When thishappens, a dummy transitional package is created -- empty anddependent on its new package. After some time, those are removedas well. The following is a list of such packages:

• combinatorics -merged into miscellaneous and specfun
• openmpi_ext - renamed mpi.
• physicalconstants - merged into miscellaneous.
• time - merged into financial.

Unmaintained packages

The Octave Forge project is a location to develop multiple packages for GNUOctave. With time, some packages become unmaintained, usually because the originalauthor no longer requires it and no one steps up to take its position. Without amaintainer or active user base, and as Octave evolves, we do not know how usablethey are, so we can no longer honestly recommend their use.

They are still stored and release tarballs can be downloaded from ourFile Release System(same for the very oldmonolithic releases) .However, many of them have accumulated bug fixes and new features in themercurial orSVNrepositories, it simply happens that no maintainer has prepared a release.Because of this, we encourage users to check the development sources, not the releasedtarballs. Furthermore,bug reports for those packagescontinue to be welcome, and anyone wishing to take up the position of maintainer, please contactus through themaintainers mailing list.

The complete list of unmaintained packages is:

• actuarial
• ad
• ann
• audio
• benchmark
• bioinfo
• civil-engineering
• engine
• fenv
• gnuplot
• gsl
• informationtheory
• integration
• irsa
• missing-functions
• multicore
• nlwing2
• nnet
• oct2mat
• octgpr
• odebvp
• outliers
• pdb
• plot
• simp
• special-matrix
• symband
• tcl-octave
• xraylib
• zenity

參考：

[1]：http://octave.sourceforge.net/

[2]：http://octave.sourceforge.net/packages.php

總結

以上是生活随笔為你收集整理的Octave中无法使用rgb2gray()函数的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。