2004.06_Digital Picture Box-Moving Images the Easy Way from Your Camera.pdf

COVER STORY

Digital Cameras

Digital Picture Box

Digital cameras continue to replace

traditional cameras in today’s homes.

The typical Linux approach to trans-

ferring images from the camera to

the hard disk is gPhoto or the kernel-

based USB mass memory module.

Graphical front-ends like digikam

promise enhanced usability.

BY ANDREA MÜLLER

oped, sorting the prints, buying

photo corners and mounting the

prints in albums. All of these time-con-

suming tasks are now things of the past

for amateur photographers who have

moved over to a digital camera from tra-

ditional wet film equipment. Those who

have made the move, face different

issues, such as finding the best software

to run on their computer to transfer the

digital images from the camera to their

home PC. The answer for Linux depends

on the make and model of the digital

camera.

Devices that attach themslves to the

system as though they were hard disks

provide the easiest approach, allowing

users to enter a simple mount command

to give access the device. If you have a

camera that uses a special protocol to

talk to the PC, and your camera is a

recent model, you still stand a good

chance of being to access the camera

using a software produced by the gPhoto

project [1]. This article describes both

approaches, and introduces software

specifically designed for interfacing with

digital cameras.

with the VFAT filesystem, typically used

by Windows 9x. As this filesystem does

not have any permissions, the adminis-

trator can assign permissions using the

umask option. 0 is the most permissive

value and grants read and write access to

any camera directory for any user.

An entry in /etc/fstab will allow non-

privileged users to mount the camera.

Mount options allow a more restrictive

approach to permissions, such as

assigning a usbusers group permissions

to delete files on the camera. After creat-

ing the group, and defining the

mountpoint, the entry might appear as

follows:

Mounting a Camera

Some cameras, such as the Aito or Casio

Exilim series, attach to a system as a

SCSI hard disk, just like a USB memory

stick is connected. You can use the

mount command to mount the camera

device, checking your /var/log/messages

file to discover the right device:

Feb 1 19:27:18 aries kernel: U

SCSI device sdb: 20208 U

512-byte hdwr sectors (10 MB)

Feb 1 19:27:18 aries kernel: U

sda: Write Protect is off

Feb 1 19:27:18 aries kernel: U

sda: sda1

/dev/sda1 /mnt/usb auto users, U

noauto,gid=333,umask=002, U

showexec 0 0

The following command, issued by root,

mounts the camera it detected as sda1 :

The gid entry is followed by a numerical

ID, as stored in the /etc/group file. All

members of the group have read and

write access to the camera. The users

entry, in contrast to user , allows non-

privileged users to unmount the camera,

mount -t vfat /dev/sda1 U

/mnt/usb -o umask=0

in /mnt/usb . The devices are formatted

June 2004

www.linux-magazine.com

Digital Cameras on Linux

B uying films, having them devel-

Digital Cameras

COVER STORY

despite not having mounted the camera

themselves.

showexec works around a problem that

stems from the fact that VFAT does not

have a rights system. Users need to be

assigned execute permissions in the

umask , to allow them access to the

directory structure. One side effect is that

normal files are tagged as being exe-

cutable. Some Linux programs, such as

older versions of the Rox file manager,

refuse to display a preview for exe-

cutable images. You can use showexec to

work around this, as it emulates Win-

dows behavior. Files with the suffixes

.exe , .bat , and .com are tagged as exe-

cutable, but no others (see Figure 1). The

fstab entry allows normal users to mount

the camera in /mnt/usb using mount

/dev/sda1 .

Suse Linux users can avoid this man-

ual work. The hotplug daemon

automatically creates an appropriate

fstab entry, as soon as a USB mass mem-

ory device is attached.

You can use more or less any file man-

ager to transfer the image files from the

camera device to your hard disk. If you

prefer a specialist program, try Digikam

[2]. This is the only camera front-end

that works with gPhoto 2 and also sup-

ports USB mass memory devices.

However, this will also require you to re-

compile the graphical front-end, and

gtkam , as this tool will not typically run

with the later version if it is linked

against an older library.

Before you go to all this trouble, you

should enter the gphoto2 --list-cameras

command to find out which devices are

supported by the version supplied with

your distribution. If you draw a blank for

your model, you can surf to [3] to check

the compatibility list for the current

gphoto2 version.

More recently, gPhoto 2 has improved

support for new models. Many of today’s

cameras use the Picture Transfer Pro-

tocol (PTP) [4], which ensures a simple

file transfer between PTP devices. This

removes the need for special drivers, and

allows any computer to exchange data

with any other PTP-aware devices with-

out installing additional software.

These devices do not need to be

limited to cameras and computers;

exchanging data with cellphones or

printers is just as easy. PTP-cameras run

“out of the box” on Windows XP and

MacOS X.

ring image files to disk. Other com-

mands, such as outputting lists of image

files, led to reproducible I/O errors; GUI-

based front ends only rarely worked.

Stability improved dramatically with ver-

sion 2.1.3. However, a camera explicitly

mentioned in the list of supported

devices will be better supported than a

generic USB PTP Class Camera . This fea-

ture is still in the test phase.

Permissions

If your camera is supported, you still

have to deal with the problem of per-

missions, unless your distributor has

taken care to allow users other than root

to access the camera. USB cameras are

detected by the system as entries below

the mountpoint /proc/bus/usb . This is

where the USB device filesystem is

located; the kernel generates the filesys-

tem generically in a similar way to the

/proc pseudo-filesystem [5]. Permission

changes are lost each time you reboot.

There are two ways to provide users

access to the camera:

• Changing the mount options for the

USB filesystem;

• Dynamically setting permissions using

the hotplug daemon.

The first approach is the simpler of the

two. The following /etc/fstab entry

Enhanced Support thanks to

the PTP Standard

Although the standard was published

back in 2000, very few manufacturers

were prepared to adopt it originally –

Kodak and Sony were among the pio-

neers. Fortunately, other manufacturers

have begun to appreciate the advan-

tages, such as cost savings, as they no

longer need to produce their own dri-

vers.

gPhoto 2 introduced PTP camera sup-

port in June 2002. It was fairly spartan at

first, and just about capable of transfer-

The gPhoto Project

gPhoto 2, which reached version 2.1.4 in

January 2004, consists of two compo-

nents: the libgphoto2 library, which

supports more than 400 camera types,

and the gphoto2 command-line program,

which allows users to access supported

cameras.

The project has its roots in

gphoto0.4.x . The older version had an

integrated graphical front-end and a

monolithic architecture. gphoto2 has a

modular structure, and was completely

re-written by its developers. The first

stable version was released for down-

loading in February 2002. New versions

of the software are released every few

months, with beta versions and pre-

releases to stop the gap between stable

releases, and allow users to test new

cameras.

As the versions included by distri-

butions tend to lag behind the current

state of development, users with new

models will need to compile the sources.

none /proc/bus/usb usbfs U

devmode=0664,devgid=333 0 0

mounts in /proc/bus/usb with read and

write permissions for user and groups

with the ID 333 (this is usbusers on our

system). Users who are not members of

this group have read access only.

These mount options are valid for any

USB device and not just for the camera.

Figure 1: The mount option “showexec” copies Windows file permissions under Linux.

www.linux-magazine.com

June 2004

COVER STORY

Digital Cameras

The hotplug daemon provides a

more elegant approach to solving

this problem. It monitors the sys-

tem’s USB ports, and recognizes

any attached USB devices by

their IDs, which are stored in

files below /etc/hotplug . De-

pending on your distribution, the

daemon parses either the

/etc/hotplug/usb.usermap or /etc/hotplug/

usb/usbcam.usermap file for the camera.

Figure 2: gPhoto 2 recognizes newly attached cameras automatically

by the USB connection.

Intuitive Filenames

The program can do more than

this. Digital cameras assign

fairly non-intuitive filenames to

images, but gphoto2 can change

the names when downloading

files. To do so, specify the --file-

name parameter, followed by a

name. --filename accepts typical

date format strings, such as %y , %m ,

and %d for year, month, and day. Also,

%n specifies a number, %C specifies a

file suffix, and finally %f specifies a file-

name without a suffix. gphoto2 -P

--filename birthday_john_%n.%C down-

loads the photos from the camera and

constructs a filename using the string

birthday_john_ , the image number, a

dot, and the file suffix.

The parameters -T and -t number(s)

download any or a selection of thumb-

nails for your photo collection. If you

have a camera that can store audio clips

in addition to images, you can specify --

get-audio-data number(s) or --get-all-

audio-data to access these files. To make

room for new images, enter --delete-files

number(s) and --delete-all-files .

The features that gPhoto 2 offers de-

pend to some extent on the attached ca-

mera. gphoto2 -a will output the features

of the attached device (see Figure 4).

Some cameras allow you to upload

image files. The -m flag, followed by a

name, creates a directory on the camera,

and gphoto2 -u filename uploads files.

The output from gphoto2 -a is not

entirely reliable. Although the driver for

our lab camera is not supposed to sup-

port capture according to the program, it

is possible to remotely control the cam-

era, and gphoto2 --capture-image will

capture an image. Unfortunately. the --

capture-sound option led to reproducible

I/O errors in our Linux labs.

The --shell parameter allows users

to navigate the camera directories, just

start with usbcam , and then add the cur-

rent camera ID to the end of the file:

Scripting

When the daemon connects to a device,

it calls the /etc/hotplug/usb/usbcam

script, which sets permissions for the

attached camera. libgphoto2 provides

four sample scripts. If you built the pro-

gram yourself, you will find them in the

source code directory below packaging/

linux-hotplug . Most distributions store

them below /usr/share/doc/libgphoto2-

versionnumber .

The four supplied sample scripts con-

sist of: usbcam.group , where the

administrator enters the group to be

assigned the correct permissions, usb-

cam.user, which expects the name of the

user to be granted permissions, usb-

cam.x11-app, which will automatically

launch a gPhoto front-end, and usbcam.

console .

The script requires PAM [6], which is

installed by default on Red Hat or Man-

drake Linux. It assigns all permissions

for the camera to the user logged on to

the console. If you build your own

gPhoto version, you will need to update

usbcam.usermap using the following

command:

/usr/local/lib/libgphoto2/ U

print-usb-usermap >> U

/etc/hotplug/usb.usermap

Setting up the camera like this allows

normal users access. A graphical front-

end is not necessarily required. The

gPhoto 2 command-line tool provides a

wide range of functions. The following

syntax:

gphoto2 --auto-detect

shows our camera as detected by the

program (see Figure 2).

Command-Line Access

to the Camera

Just a few flags are required for basic

access. -l lists the directories, -L adds the

filenames. Users can refer to the serial

numbers in this output (see Figure 3

below) using the -p number(n) syntax,

to filter specific files. -P refers to all the

images found in the current working

directory.

If you only want to transfer specific

image files to the hard disk, you can

specify these files as gphoto2 -p 2,4,5 to

download images 2, 4, and 5, or specify

a range, as in gphoto2 -p 2-4 . It is quite

simple to exclude files from a range. For

example, gphoto -p 2-6,4 downloads the

images 2, 3, 5, and 6, but not file num-

ber 4.

/usr/local/lib/libgphoto2/ U

print-usb-usermap > U

/etc/hotplug/usb/usbcam.usermap

If your distribution parses usb.usermap ,

you will need to delete any lines that

Figure 3: gPhoto 2 displaying a list of the images on the camera.

Figure 4: The -a flag lists the camera’s capabilities, telling you if the camera

supports thumbnails for example.

June 2004

www.linux-magazine.com

Digital Cameras

COVER STORY

like a local filesystem. Users

can enter gphoto2 --shell to

pop up the program’s internal

command-line. If you have

ever used a text-based FTP

client, you should have no

trouble finding your way

around.

The oldest contender is

gtkam [7], which is a fairly

staid affair (see Figure 5) that

provides only basic function-

ality. Selecting Camera | Add

Camera | Detect tells the pro-

gram to access gPhoto 2’s

auto-recognition function.

You can use a file manager

style tree view to navigate the

directory structure on a sup-

ported camera. GTKam

displays images in the right-

hand panel. The thumbnail

view provides an initial over-

view. The File menu allows you to

download all or selected images, and

delete any images that you have success-

fully transferred to your hard disk.

digikam provides far more user conve-

nience. Instead of deserting the user

after downloading the image files, the

tool also manages images on the hard

disk. Images are organized in albums,

which are in fact simple directories. The

program will display the albums rather

Additional Functions

help in the gPhoto2 shell lists

the available commands, help

commandname displays the

syntax for individual com-

mands. ls lists the files. cd

changes to another camera directory.

delete file deletes a file. get file starts

downloading a photo to the current

working directory, and get-thumbnail

does the same thing with the thumbnail

for the current image. If you open the

gPhoto shell in a directory where you do

not have write privileges, you can type

lcd directory to change to another local

directory. The show-exif file command is

designed to display the meta-data for an

Figure 5: Clear-cut and functional: the GTKam GUI.

image file, but refused to work in our

lab. q , quit , or exit quits the program’s

command line.

Graphical Front-Ends

If you are unhappy with the command

line, you can try one of the graphical

front-ends for gphoto . There are several

currently competing for the position

of the amateur photographer’s best

friend.

EASY TO BUY • EASY TO SET UP • EASY TO SEE

one elephant...

Be a host with the most for

the least using our world class

web hosting services. From just

£30 a year.

two elephant...

Count on us for

big web benefits

Do the business brilliantly with our

EasyVserver. Launching your own web busi-

ness has never been so affordable. Choose from

4, 8 or 16 Gigabyte options. There’s no set up

fee and web host manager makes managing

multiple domains and email accounts easy.

three elephant...

Make a name for yourself with an

unforgettable e-mail address from the UK’s

favourite domain name registrar. Why be

boring? Give hotmail the cold shoulder. Give

yahoo the old heave-ho. And be unique,

such as nothingon@all.tv, rich@thirty.me.uk,

hrh@buckhouse.info, tuff@thetop.org.uk.

four elephant...

five elephant...

Access email anytime, anyplace, anywhere

with Easypost. That’s our brilliant web mail package

that enables you to pick up and send email using your

domain name, making you look more professional. It’s

also anti-spam and anti-virus to ensure you don’t pick

up anything nasty along the way.

From only £3.99 a year.

Log on in seconds and refresh your

business image the easy way.

Log on now and find out why 1/2 million

customers already put us first.

Established in 1997 with over 1 / 2 million customers. Accredited ICANN registrar & nominet member. Prices exclude VAT.

COVER STORY

Digital Cameras

than providing an overall view of the

complete filesystem tree. Thumbnails are

displayed in the right-hand panel (see

Figure 6). You can drag & drop an image

to copy or move it to another album in

the tree view.

• Mail function with options for chang-

ing the size and compression rate of

the files. Works with KMail, Sylpheed,

and Mozilla.

With regards to managing and archiving

digital images, Digikam has developed

features that cater to user’s every need.

flphoto [8] takes a different approach.

The program is really an image manage-

ment tool that offers camera access as an

add-on. The tool lacks a separate option

for deleting images from the camera. The

Album | Import | Camera dialog does

provide a simple workaround, however.

When you launch this item, FLPhoto

autodetects the camera, and displays

preview thumbnails of the

images in the transfer window

(see Figure 8).

The image management fea-

tures themselves are very

advanced. The program works

with albums, which are actually

text files containing the names

of the images in the album. If

you select Image | Remove to

delete an image from an album,

this does not delete the image

file physically from your disk.

The preview bar at the bottom

of the window is more practical

than the typical tree view, as it

leaves more room for images on

the desktop (see Figure 9).

If you prefer to use the same

program for all of your file oper-

ations, you might prefer to stick

with the KDE file manager,

Konqueror, when transferring

images from you camera to disk.

Thanks to the camera Kioslave,

the KDE file manager tool can

use the libgphoto2 library to

access any supported digital

cameras, just as though they

were a locally attached filesys-

tem. Typing camera:/ in the

address line as the URL launches

the auto-detect process, and tells

Konqueror to display the cam-

era’s root directory.

Digikam, the Shooting Star

Digikam demonstrates an open

approach when setting up a

camera. Besides models sup-

ported by gPhoto 2, it also

provides access to USB mass

storage devices. You can select

USB Mass Storage and enter a

mountpoint (see Figure 7) to set

up this type of device. Selecting

Camera | Connect mounts the

device in the file system.

Besides functions for down-

loading and deleting images,

Digikam also has an upload

function. To view images at full

scale, you can optionally open

your images in an external

viewer, rather than in the inter-

nal viewer. KDE programs such

as kuickshow and kview are

examples of external viewers. A

slideshow function, which

optionally supports filename

labels, rounds off the program.

The new version 0.6.0 may

already have been released by

the time this article appears.

Ve rsion 0.6.0 will again have

added functionality. Digikam

uses a plug-in architecture in the

new version, allowing develop-

ers to extend the program’s

functionality. Release Candi-

dates 1 and 2 already had a

feature-rich plug-in collection

that provide the following exten-

sions among others:

• Slideshow with effects;

• MPEG encoder which can use

the mjpeg -Tools and Image-

magick, to create videos for

VCDs, SVCDs, or DVDs;

• HTML Gallery, an extension

of the Konqueror Gallery plug-

ins;

• Comment editor;

• Photoprint Wizard to arrange

multiple images on a single

page;

• CD archival (needs K3b);

Figure 6: Tree view, camera view, and preview in Digikam.

Figure 7: Digikam also supports cameras that the system detects as

USB mass storage devices.

Specialists for Exif

Information

Images from some digital cam-

eras include so-called Exif

(Exchangeable Image File For-

mat) [9] headers, which store

information such as a time-

stamp, the focal distance, the

flash mode, and the camera

type. Users who want to retain

this meta-information while pro-

cessing images cannot use

traditional image manipulation

tools to do so, as the meta-infor-

Figure 8: Importing images from a digital camera in FLPhoto.

June 2004

www.linux-magazine.com

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: