The Definitive Guide to ImageMagick

Michael J. Ross writes "To modify a digital image, most computer users turn to a GUI-based image processing application, such as Photoshop. However, while Photoshop and many other similar programs can process multiple images in batch mode, they still require manual usage, and thus typically are unable to process images via a command line or within a second application. Those capabilities call for a programmatic digital image manipulation tool such as ImageMagick, which is explored in a relatively new book, The Definitive Guide to ImageMagick." Read the rest of Michael's review.

The author of this title is Michael Still, a programmer who gained experience with ImageMagick during his eight years of working on imaging applications, as well as writing articles on ImageMagick for IBM DeveloperWorks. Apress maintains a Web page for the title, where a visitor can purchase the electronic version of the book, read its table of contents, or download its source code or a sample chapter (Chapter 4 — Using Other ImageMagick Tools) in PDF format. They also have a link where readers can submit errata — and apparently be the first to do so, as there are no existing errata listed on the Web page.

The book's 335 pages are organized into a dozen chapters, following an introduction and a few other standard sections, including a forward written by ImageMagick's principal architect, Christy, who briefly explains the product's 20 years of history, development, and lack of decent documentation. That is where this book is intended to fill the gap, and Christy notes that most future questions about ImageMagick will be answered by pointing people to this book, as is also noted on ImageMagick's homepage.

The first chapter of the book explains how to install and configure ImageMagick, for several Linux distros, as well as Microsoft Windows — using the precompiled versions, or by compiling from ImageMagick's source code. The chapter is wrapped up with a brief description of ImageMagick's online help, debug output, verbose output, and version information. The next ten chapters fall into two categories: ImageMagick usage as a standalone, and from within other applications. The first category of chapters covers basic image manipulation, compression, other metadata, ImageMagick tools, artistic transformations, other image transformations, and drawing commands. The second category discusses how to utilize ImageMagick from within programs written in Perl, C, Ruby, and PHP. The 12th and final chapter is quite brief, and describes where to find online help (Web sites, blogs, mailing lists, and forums) and where to report any apparent bug in ImageMagick.

For Windows users, the first chapter may begin badly, as the author fails to explain which precompiled version the reader should select if they wish to install ImageMagick on a Windows PC. For each version, there are four flavors to choose from. But which one is right for the reader? "static" vs. "dll?" "Q16" vs. "Q8?" What are the differences? The ImageMagick Web site and FTP file listings appear to have no README file or installation help file to explain which flavor you should download. The book should provide some assistance here, but does not. The former topic, static versus DLL, is mentioned only in reference to compiling ImageMagick from source — information which the reader will probably never see, should they choose to install the precompiled binaries and get started on ImageMagick as quickly as possible.

The latter topic is not covered at all — not even in the index, where a "quantum depth" entry would be useful. For those readers who are interested, "Q8" indicates 8 bits-per-pixel components, and "Q16" means 16 bits-per-pixel. The latter allows one to read or write 16-bit images without losing precision, but requires twice as much resources as Q8. Apparently Q16 is the best choice for medical or scientific images, or those with limited contrast. Otherwise, Q8 should be sufficient, and offers greater performance.

The material most likely to be read, referenced, and valued in this book, is the chapters devoted to explaining how to use ImageMagick for resizing, compressing, transforming, and drawing digital images. Most of these first-category chapters begin with a concise summary of the theory put into practice throughout the rest of the respective chapter — a wise inclusion in each case, since even the most experienced computer programmers and other users have had no instruction or experience in image theory. All of these chapters do a competent job of explaining what each ImageMagick command is used for, and then illustrating it with a straightforward example.

The most glaring deficiency in these chapters, and the book as a whole, is that far too many of the book's figures (digital images, naturally) fail to reflect what is intended to be conveyed by each figure. This is primarily because they are all in black-and-white, and in many cases do not offer the size and resolution necessary. In other words, there are many cases where the "before" and "after" images look almost identical. In the cases of color manipulation, most of those black-and-white images are of little value — occasionally laughably so.

The second-category chapters, covering ImageMagick usage with Perl, C, Ruby, and PHP, proved disappointing, primarily due to their narrow focus, and lack of tips, recommendations, and coverage of the APIs' capabilities. The details are presented in the form of a single example for each language. For instance, the Perl chapter devotes too many pages to source code listings of a Perl program written by the author, that few readers would probably download from the publisher's Web site, much less read.

Nonetheless, this book should be useful to any programmer interested in making the most of ImageMagick's capabilities, and that is not just because it is the only ImageMagick book on the market. Michael Still certainly had his work cut out for him when he agreed to document the bulk of what ImageMagick can do. It is unfortunate that the color images that he created for the book cannot be seen by the reader, and that the Windows binary versions and ImageMagick APIs, were given short shrift. We can hope that future editions of this book will be significantly strengthened, such as including color and higher resolution images where needed — even if it requires grouping them together within the book, if that reduces production costs.

Lastly, it should be mentioned that, as a smaller technical publisher, Apress is not resting on its laurels, and is not only scheduled to release an impressive variety of programming books this year, but their customer support — at least in my experience — was outstanding, as there was a problem with the shipping of this title, and they bent over backwards to make it right.

Michael J. Ross is a freelance writer, computer consultant, and the editor of the free newsletter of PristinePlanet.com."

---

You can purchase The Definitive Guide to ImageMagick from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

yes, you can command line photoshop

[Anonymous Coward]

Just create an action which does what you want, then you can export an "EXE" which takes as command line argument the file you want to process, and optionally, the output. Works like a charm.

Re:yes, you can command line photoshop

[Anonymous Coward]

Oh, yes, that's much easier than

for img in `ls *.jpg`
do
  convert -sample 25%x25% $img thumb-$img
done

And the million other things you can do from the command line without making task-specific exes.

Re:yes, you can command line photoshop

[pclminion (145572)]

for img in `ls *.jpg`

Am I the only person who laughed out loud?

Re:yes, you can command line photoshop

[lubricated (49106)]

only after you pointed it out. I kind of scanned over it and missed it the the first time ;) .
Yeah, that was a rookie move.

Re:yes, you can command line photoshop

[foxtrot (14140)]

Am I the only person who laughed out loud?

Probably not, but I think it's kinda silly. If you're on a machine where you're worried about spawning off one more process, I feel sorry for you. :)

Remember, there's More Than One Way To Do It. That's kinda the beauty of Unix. I do like that 'for i in *.jpg' takes a lot fewer keystrokes, mind, but just because it uses fewer keystrokes and doesn't exec ls doesn't make it the Only Right Way.

Indeed, for some things, it may not be the Right Way at all. Ferinstance:

for i in `ls fullsize`
do
convert -scale 800x800 fullsize/$i $i
convert -scale 150x150 fullsize/$i thumbnails/$i
done

It's cheaper to exec ls here than it is to crunch $i each time to strip 'fullsize/' off the front. If you really wanted to streamline it (and if you're that worried about it, why the heck are you writing a shell script?) you could throw $PWD at a temporary variable, cd into fullsize, run your converts, but why bother with the extra typing or lines of code when this runs correctly, makes sense, and is only exec'ing the ls once?

But really what it boils down to, to me, is if exec'ing ls once instead of using the shell builtin * is causing problems on your system, you've got bigger problems than your shellscript-fu.

-F

Re:yes, you can command line photoshop

[garcia (6573)]

You know, I don't know what the problem is but whenever I try to do a large batch (20 or so images) with ImageMagick inside a loop it hangs my machine. It only started happening when I upgraded to a 7MP camera and the images (not at full resolution either!) were in the 4.5MB range.

Now I have to break the images up into batches of 5 and run the script each time for those. Bleh.

Re:yes, you can command line photoshop

[kesuki (321456)]

if you're using windows, and are taking directly from the camera or memory card, it's a bug in the Mass storage class driver.

The MSC driver can hard lock (requireng removal of the USB device).

If the problem happens no matter where you locate the images (local hd) then it've got no clue what your problem is. but from the sounds of it you've been using IM to parse pics from your cmaera directly to some local folder, likely the new camaera has faster memory that causes the MSC lock up issue (it does not happen

Re:yes, you can command line photoshop

[Anonymous Coward]

Real_men_don\'t_put_spaces_in_file_names.

Re:yes, you can command line photoshop

[Anonymous Coward]

don't be a dummy

for i in *jpg; do
  convert -sample 25%x25% "$i" "thumb-$i"
done

works perfectly with any special characters, including spaces and newlines, in the filename

Re:yes, you can command line photoshop

[niskel (805204)]

I was refering to the original script that used `ls *.jpg` instead of simply *.jpg. The original script will choke on images with a space in the file name.

Re:yes, you can command line photoshop

[Mr. Underbridge (666784)]

works perfectly with any special characters, including spaces and newlines, in the filename

Wow. Anyone who puts newlines in a filename should be beaten publically.

Re:yes, you can command line photoshop

[Black Perl (12686)]

Command-line control implies a bit more than creation of a canned .exe file. OK, let's say I need to automate the creation of graphical "Tabs" for a web layout. They have to contain text (determined at runtime from, say, a database), blended and drop-shadowed. Can I do this using the technique you mentioned? Nope. I can do it in imagemagick though.

Re:yes, you can command line photoshop

[Short Circuit (52384)]

On Windows, maybe. But what about Linux? And what are the license restrictions for including the exported EXE with other applications?

Re:yes, you can command line photoshop

[tpgp (48001)]

Just create an action which does what you want, then you can export an "EXE" which takes as command line argument the file you want to process, and optionally, the output. Works like a charm.

Maybe the author should have said 'useful commmand line processing' or similar.

1) Exes are not very useful for osx or linux users.

2) You need a copy of photoshop for every server you wish to run your exported exe on.

3) You have to create a different 'exe' for each action.

Photoshop is not even slightly useful for the sort of areas that imagemagick excels in.

Re:yes, you can command line photoshop

[base_chakra (230686)]

Just create an action which does what you want, then you can export an "EXE" which takes as command line argument the file you want to process, and optionally, the output. Works like a charm.

I've batch-processed sets comprising about 2,500–4,000 images (greyscale GIFs) both with command-line tools and with Photoshop CS. On each occasion, Photoshop took several hours longer than the specialized CLI apps to complete the jobs. The difference is even more dramatic when executing Photoshop Actions from within Photoshop, since the screen updates further increase processing time (an effect only slightly mitigated by hiding subwindows).

Re:yes, you can command line photoshop

[niskel (805204)]

Can you do that from a server? Can you do it for free? Can you do it for less specific tasks than a single custom EXE can do? Can you do it on platforms that aren't Windows or OSX?

ImageMagick is good stuff.

[tetrahedrassface (675645)]

Imagemagick is good stuff, ive used it for a while now. Although I didn't buy a book to learn how, i just went here, for some great samples of uses:
http://www.cit.gu.edu.au/~anthony/graphics/imagick 6/ [gu.edu.au]
PIL isn't too shabby either http://www.pythonware.com/library/pil/handbook/ind ex.htm [pythonware.com]
Powerful stuff, maybe the book is not that great i don't know, but imagemagick and PIL are!

Better image examples online

[digitaldc (879047)]

In other words, there are many cases where the "before" and "after" images look almost identical. In the cases of color manipulation, most of those black-and-white images are of little value -- occasionally laughably so.

Haha, that was funny...well if you need to see what it actually does, their examples site [imagemagick.org] has some better images.

GraphicConverter

[andyring (100627)]

GraphicConverter on the Mac has some fairly powerful built-in scripting/workflows you can specify for a whole bunch of photos at once. And, it's shareware too. Such as I've used it to all at one time for 100+ photos, perform an "auto levels", reduce the file size so they're easier to e-mail, and create a basic thumbnail Web-ready batch. You can do probably 100 or more tasks this way.

Re:GraphicConverter

[mrchaotica (681592)]

Free Software > shareware.

Also, ImageMagick is more useful for integration with Unix-style shell scripts (as opposed to Automator actions or Applescript, which I suspect GraphicConverter would support instead).

Re:GraphicConverter

[tpgp (48001)]

GraphicConverter on the Mac has some fairly powerful built-in scripting/workflows you can specify for a whole bunch of photos at once.

Not even remotely like imagemagick - why don't you just download the os x [finkproject.org] native port?

And, it's shareware too.

From the GraphicConverter website [lemkesoft.de]:

The shareware fee is $30.

I don't even know what shareware means anymore - $30?

Such as I've used it to all at one time for 100+ photos, perform an "auto levels", reduce the file size so they're easier to e-mail, and create a basic t

ImageMagick + Rails == good

[tcopeland (32225)]

I did some nice charts [blogs.com] for the indi [getindi.com] admin pages; worked out really nicely thanks to Gruff + RMagick.

I did have a spot of trouble getting the fonts working at first, but once that was fixed, it was easy to create some nice charts with very little code.

Re:ImageMagick + Rails == good

[mrchaotica (681592)]

gnuplot might be good for that, too.

Wikipedia uses it

[interiot (50685)]

For what it's worth, Wikipedia uses ImageMagick to automatically resize png/jpeg/gif images for articles (eg. photos uploaded at 1920x1080 can be displayed at 300x169 in an article). So it's good enough to run on a high-traffic website (and is pretty flexible for ad-hoc command-line use too).

Re:Wikipedia uses it

[theurge14 (820596)]

Just to clarify, ImageMagick is not called everytime someone views that smaller thumbnail everytime they view the Wikipedia article, ImageMagick is called upon only when the orginal article was edited, the output is saved by MediaWiki as a totally new image into an images folder. From then on, it's a straight HTML img tag.

I just wanted to make sure people didn't think ImageMagick is being called upon the MediaWiki software every time the image got a page hit.

Not just for command line use!

[PeeAitchPee (712652)]

ImageMagick's function library is also accessible through a variety of APIs for your favorite language [imagemagick.org] -- scripting or otherwise. If you haven't used it, try it . . . it's GPL and it Rawks (with a capital "r"). ;-)

Scripting

[base_chakra (230686)]

ImageMagick's function library is also accessible through a variety of APIs for your favorite language -- scripting or otherwise. If you haven't used it, try it . . . it's GPL and it Rawks (with a capital "r"). ;-)

While I use (and love) ImageMagick, it's worth noting that Photoshop has similar (but not totally analogous) capabilites:

http://partners.adobe.com/public/developer/en/phot oshop/sdk/PhotoshopScriptingGuide.pdf [adobe.com]

Unfortunately, Photoshop's scripting host only supports JavaScript, VBScript, and AppleSc

Flickr Hacks

[jbum (121617)]

My book, Flickr Hacks [amazon.com], contains a number of examples of using ImageMagick (via the Perl API) with Flickr. This is one area where it really shines. I used ImageMagick to create these mosaic posters [krazydad.com], the Flickr Colr Pickr [krazydad.com] and other cool things.

check out netpbm too

[resfilter (960880)]

those interested in command line image processing, should check out netpbm [sourceforge.net] too. it's really neat

instead of a single image processing program, netpbm is a massive collection of programs all using a small set of proprietery formats (they are all compatible with each other). you use pipes for communication between them, giving you some more flexibility.

for example:

pngtopnm foo.png | pnmscale -xsize=600 ysize=400 | pnmtojpeg > foo.jpg

the other advantage is, their proprietery formats were designed to be easy to use, so coding your own netpbm programs is much easier than rewriting imagemagick for a specific task.

Re:check out netpbm too

[Tet (2721)]

those interested in command line image processing, should check out netpbm too.

I couldn't agree more. For a start, a single monolithic app like ImageMagick is just not the Unix way. It means that to add functionality, you need to recompile the application. With netpbm, if you want a new feature, you just write a filter and stick it in the pipeline. Much easier, and much more flexible. In the past, my only gripe was that netpbm (and pbmplus before it) was unable to handle transparency in image. Fortunately

Which Precompiled Windows Version?

[Goo.cc (687626)]

"The ImageMagick Web site and FTP file listings appear to have no README file or installation help file to explain which flavor you should download."

From http://www.imagemagick.com/www/binary-releases.htm l [imagemagick.com] :

"The Windows version of ImageMagick is self-installing. Simply click on the appropriate version below and it will launch itself and ask you a few installation questions. Versions with Q8 in the name are 8 bits-per-pixel component, whereas, Q16 in the filename are 16 bits-per-pixel component. A Q16 version permits you to read or write 16-bit images without losing precision but requires twice as much resources as the Q8 version. Versions with dynamic in the filename include ImageMagick libraries as dynamic link libraries. If you are not sure which version is appropriate, choose ImageMagick-6.2.6-3-Q16-windows-dll.exe."

I know that its not a readme file but the website seems pretty explainatory. You are right about the FTP site, however.

Batch processing

[AaronW (33736)]

For doing batch processing of photos I have been using Bibble Pro [bibblelabs.com] for Linux lately. I like it since it has good support for the raw format of my SLR and has a lot of batch processing features. For example, it's easy to select a group of 50 photos and adjust the white balance, or use the one click lens distortion fix on all my photos. Best of all, it runs under Linux. It gives me the best of both worlds. It gives me batch processing as well as the ability to individually make changes to each picture. I.e. I can bring out the shadows in a group of pictures, then straighten a couple of them if the camera was crooked and crop them as needed. It also does everything at 16 bits per color.

Now, granted, it does not run on the command line, but it easily lets me select a source and target directory to batch process as well as letting me select individual pictures. I can't really compare it with ImageMagick since I haven't used it directly.

-Aaron

NetPBM

[Azul (12241)]

Hmm, I tend to find the approach of NetPBM [sourceforge.net] easier to work with: having lots of separate utilities each doing a single simple thing and making it easy to use them together by piping the output of one to the next. Besides, reading/writing PBM files is trivial so you can very easily use these tools from your programs (by piping your image through them) or you can very easily create new filters that integrate well with the rest. I recommend you check out NetPBM.

If you need automatic processing of many images (the sort of thing ImageMagick is being praised for), I recommend you check it out.

Two words: UNSTABLE API

[mi (197448)]

ImageMagick's API is notoriously unstable and new releases don't even bother with backwards compatibility. Once in a while, even the command line options change between releases breaking existing scripts (such as ImageIndex [edwinh.org], for example).

If you wish to write your own programs using a powerful image-processing library, you will, most likely, prefer the fork of ImageMagick called GraphicsMagick [graphicsmagick.org].

i had that same question

[acvh (120205)]

until I read the FA.

"The material most likely to be read, referenced, and valued in this book, is the chapters devoted to explaining how to use ImageMagick for resizing, compressing, transforming, and drawing digital images."

OK, I don't get the drawing part - but the rest seem amenable to batch processing.

Re:i had that same question

[eh2o (471262)]

watermarking, annotations, making buttons... etc. typical applications requiring batch drawing.

Re:Manual vs. Automatic

[wanerious (712877)]

As an example, in my previous job for a weather company, we'd generate large images of geographic data for a certain area of interest, and separately generate radar or satellite or lightning maps over the same area. We'd then use ImageMagick to combine all the separate images together, along with further generated warning areas, icons, and forecasts representing weather phenomena of interest (tornadoes, mesocyclones, hurricanes) and usually some sort of written annotation (time of image, source). ImageMagick was/is really useful.

Re:Manual vs. Automatic

[pilkul (667659)]

Maybe you don't need it, but a lot of people do. For example, game developers often work with loads of images in similar formats. As a really simple example, you might want to convert a thousand files from gif to png. Or let's say you have 100 images containing blue text and you want to make the text white.

Re:Manual vs. Automatic

[syphax (189065)]

Why would one need batch-sized automatic image editing?

Examples of edits that don't need to be manual: Thumbnails. Resizing. Addition of timestamps/watermarks/copyright info. Conversion to other formats. Motion detection. Mosaics. Proof sheets.

Gentle readers: just because something doesn't seem useful or make sense to you does not mean that it is categorically useless or senseless for everyone.

Re:Manual vs. Automatic

[fan777 (932195)]

Automatic editing is especially useful for web applications where image manipulation occurs based on form choices or happens in the background e.g. thumbnails being created on the fly, allowing certain types of filtering, etc.

In my senior year of college, we came up with a project to create an online photo storage and editing site much like Yahoo's Flickr. This site allowed users to crop photos, transform pictures to black and white, and adjust contrast amongst other things. We used ImageMagick to do all

Re:Manual vs. Automatic

[prockcore (543967)]

Why would one need batch-sized automatic image editing?

How do you think flickr makes perfect square thumbnails automatically?

convert in.jpg -thumbnail x200 -resize '200x' -resize 50% -gravity center -crop 100x100+0+0 +repage out.jpg

Any website that takes a user-uploaded photo needs to do something to it. From thumbnails to capping the image size.

video?

[poptones (653660)]

Export an avi to a folder full of pngs, attack it with imagemagick and a few batch scripts and you have a substantial amount of functionality. It's easy to advance single frame just by opening your favorite image viewer and clicking through the directory, and tweaking a single frame to perfection is as easy as saying "open in gimp."

I am a photographer...

[temojen (678985)]

My pictures are carefully composed and exposed. I set the whitebalance when I scan the negatives. Once the scanning is done, I run a batch job (over possibly hundreds of images) which opens each file (16 bit tiff), scales for printing at 12x18, 8x12, 8x10, 6x8, 5x7, and 4x6, saving as 100% quality jpeg, scales to 1024x768, 600x400, and 150x150, padding with borders if nescesary, rotating to portrait if nescesary (from a list), watermarks and signs them, and saves as 80% quality jpeg. This batch job can run

Re:I am a photographer...

[temojen (678985)]

Also, the exposure latitude of digital sensors sucks compared to Reala and Portra. And I get 14MPix from 35mm, with tonality close to digital from 100iso print film, and almost as good as digital from Portra 400. Resampling down to 6x8@300 I get tonality comperable to digital from Portra 400 and the lower contrast is more flatering for images of people.

6x6 and 4x5 give tonality identical to digital with any film and you can enlarge much more while still seeing increasing detail. They're much more botherso

Re:Manual vs. Automatic

[plover (150551)]

We use it for "normalizing" images. We have a device with a fixed resolution and some pretty severe limitations on the sizes, resolutions, formats, etc., of images we can send to it.

The original developer had his "submit image here" web page load the image into some Windows "object" format, and then do a bunch of tests, like 'reject if is it > 500 pixels wide' and 'warn if color depth > 2' and 'reject if not .BMP format'. But this is horrible for the users -- they may not have the image in the required format, and some won't have the knowledge to get it into the format we require.

I told him to just inline imagemagick's convert function, and output the exact format he requires. The sanitization is now very simple: if imagemagick can read it and successfully convert it to the desired format, it's good. That means we don't even have to tell our users to use .BMP or .GIF or .whatever -- if they can get us an image in a format recognized by imagemagick, we can use it. We've published guidelines that say "if you make your image conform to such-and-such attributes, our output will be as good as we can possibly make it." We're not promising an image that is horribly tortured by Imagemagick will print as well as they desire, but at least our app won't crash if they try to feed us garbage, or try to blow us up with a 10MB .TIFF or .WMF.

Re:Manual vs. Automatic

[temojen (678985)]

If you're doing multiple transformations to the same file, PerlMagick is much faster than ImageMagick, since you only have to load and convert to internal format once for each file. One project I worked on thrashed badly as a BASH-ImageMagick script, but could be run in the background while the computer scanned (300 DPI, legal size, with a document feeder, 4ppm) as a PerlMagick script.

Disagree...

[anandamide (86527)]

Batch processing images via the commandline isn't really a mainstream activity. ImageMagick is (ASAIK) widely used by the people and applications that need such a tool. I use it professionally and personally when I need such a tool.
You might as well say that weblog analysis tools are sliding towards obscurity because they aren't featured on the cover of LinuxNewbie Magazine.

Re:OS X Automator

[mrchaotica (681592)]

More importantly, Automator would let you integrate ImageMagick with the rest of your workflow. For example, it could get your pictures off your digital camera, transform them with ImageMagick, stick them into a web page using iWeb, and upload them to your server, all automatically.

Re:OS X Automator

[niskel (805204)]

I would love to see somebody jerry rig Automater and one or more instances of Photoshop to process images for some image related web server. Especially if it showed photoshop running on the screen. It would be a hoot. Then I would laugh at the sysadmin for even thinking of doing something like that.

Re:OS X Automator

[labratuk (204918)]

Only much slower, much less flexible, tied to a GUI, tied to a proprietary platform, needing a software license for each machine and only working with applications that support it.