Simple JPEG Extension Library for Ruby

Overview

This is a simple JPEG extension library for Ruby. This library only supports reading and writing JPEG files. You can access raw RGB data if you need.

Requires

IJG's jpeg library (libjpeg)

How to build

$ ruby extconf.rb $ make

If you use VC++, run nmake instead of make.

If extconf.rb cannot find libjpeg headers and/or library, you should specify their paths by --with-jpeg-include and --with-jpeg-lib options.

Reference

module JPEG

JPEG base module.

constants

JPEG::VERSION

Version string of this library.

module methods

JPEG.read(io)

Read JPEG file from io and returns JPEG::Image object.

io must be an IO object. It will be binmode'ed.

JPEG.write(img, io, gray = false)

Write img as JPEG file to io.

img must be a JPEG::Image object. io must be an IO object. It will be binmode'ed. gray must be a true value or a false value. If gray is a true value, the written JPEG file will be grayscale image.

class JPEG::Image

Class for image data.

super class

Object

class methods

JPEG::Image.new

Create a JPEG::Image object.

instance methods

JPEG::Image#width

Returns the width of the image.

JPEG::Image#width=(num)

Set the width of the image.

num must be an Integer object. It must be more than 0.

JPEG::Image#height

Returns the height of the image.

JPEG::Image#width=(num)

Set the height of the image.

num must be an Integer object. It must be more than 0.

JPEG::Image#quality

Returns the quality of the image.

JPEG::Image#quality=(num)

Set the quality of the image.

num must be an Integer object. It must be more than 0 and less than or equal to 100.

JPEG::Image#raw_data

Returns the raw RGB data of the image.

The returned value is a String object. If the image is colored, 1 pixel is 3 bytes -- 1st byte means red, 2nd byte means green, and 3rd byte means blue. If the image is grayscaled, 1 pixel is 1 byte.

The raw data starts the pixel of left-top corner. And next 3 bytes (color) or 1 byte (grayscale) is the right pixel of it, and so on. After first line ended, the most left pixel of next line starts.

JPEG::Image#raw_data=(str)

Set the raw RGB data of the image.

str must be a String object. It must be larger than or equal to the required size. You can calculate that the size is width * C * height. C is 3 if the image is colored, or 1 if the image is grayscaled.

JPEG::Image#gray?

Returns the image is grayscaled or not.

The returned value is a true value or a false value.

JPEG::Image#bilinear(width, height)

Creates and returns a new JPEG::Image object by converting the size of the image. It converts the image by using bilinear operation.

width and height must be Integer objects. They must be more than 0.

JPEG::Image#bicubic(width, height)

Creates and returns a new JPEG::Image object by converting the size of the image. It converts the image by using bicubic operation.

width and height must be Integer objects. They must be more than 0.

JPEG::Image#auto_contrast()

Creates and returns a new JPEG::Image object which is adfusted the level of the image contrast automatically.

JPEG::Image#level(low, high, adjust = false)

Creates and returns a new JPEG::Image object which is cut the level of the image contrast.

low and high must be Integer objects. They must be more than 0 and less than or equal to 100. high must be more than low. adjust must be a true value or a false value. If true, the level of contrast will be adjusted automatically after cutting.

JPEG::Image#clip(x1 = nil, y1 = nil, x2 = nil, y2 = nil)

Creates and returns a new JPEG::Image object which is clipped from the image. If there is no argument, returns an image clipped automatically. Otherwise, requires all 4 arguments and clips (x1, y1) - (x2, y2).

x1, y1, x2, and y2 must be Integer objects or nil.

JPEG::Image#grayscale()

Creates and returns a new JPEG::Image object which is grayscaled from the image.

class JPEG::Reader

Class for reading JPEG file.

super class

Object

class methods

JPEG::Reader.new(io)

JPEG::Reader.open(io)

Create and returns a JPEG::Reader object. The object will read a JPEG file from io.

io must be an IO object. It will be binmode'ed.

JPEG::Reader.open(io) {|reader| ... }

Create a JPEG::Reader object and will pass it to the given block. After executing the block, it returns nil.

instance methods

JPEG::Reader#close

Close the object. You can never use this object to read data.

JPEG::Reader#each {|line| ... }

JPEG::Reader#each_line {|line| ... }

JPEG::Reader#read_each_line {|line| ... }

Reads the JPEG file and passes the raw RGB data of each lines to the block. The passed line will be a String object. If the image is colored, 1 pixel is 3 bytes -- 1st byte means red, 2nd byte means green, and 3rd byte means blue. If the image is grayscaled, 1 pixel is 1 byte.

JPEG::Reader#width

Returns the width of the image.

JPEG::Reader#height

Returns the height of the image.

class JPEG::Writer

Class for writing JPEG file.

super class

Object

class methods

JPEG::Writer.new(io, width, height, quality, gray = false)

JPEG::Writer.open(io, width, height, quality, gray = false)

Create and returns a JPEG::Writer object. The object will write a JPEG file to io.

io must be an IO object. It will be binmode'ed. width and hight must be Integer objects. They must be more than 0. quality must be an Integer object. It must be more than 0 and less than or equal to 100. gray must be a true value or a false value. If gray is a true value, the written JPEG file will be grayscale image.

JPEG::Writer.open(io, width, height, quary, gray = false) {|writer| ... }

Create a JPEG::Writer object and will pass it to the given block. The object will write a JPEG file to io.

io must be an IO object. It will be binmode'ed. width and height must be Integer objects. They must be more than 0. quality must be an Integer object. It must be more than 0 and less than or equal to 100. gray must be a true value or a false value. If gray is a true value, the written JPEG file will be grayscale image.

After executing the block, it returns nil.

instance methods

JPEG::Writer#close

Close the object. You can never use this object to write data.

JPEG::Writer#write_each_line { ... }

Write the return value of the block as the raw RGB data of each lines to the JPEG file. The return value of the block must be a String object. If the image is created for grayscale image, 1 pixel is 1 byte. Otherwise, 1 pixel is 3 bytes -- 1st byte means red, 2nd byte means green, and 3rd byte means blue.

JPEG::Writer#width

Returns the width of the image.

JPEG::Writer#height

Returns the height of the image.

JPEG::Writer#quality

Returns the quality of the image.

JPEG::InternalError

errors in this library.

super class

StandardError

JPEG::JERR_*

libjpeg errors.

super class

JPEG::InternalError

constants

Errno

libjpeg error code.

JPEG::UnknownError

libjpeg unknown error.

super class

JPEG::InternalError

LEGAL Issue

Copyright (c) 2007,2011 NAKAMURA Usaku usa@garbagecollect.jp All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

(1) Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. (2) Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Attention

The binary form of this library may contain the libjpeg's code. In such case, you might have to consider to the license of libjpeg.