ImageMagick - Frequently Asked Questions
Description: ImageMagick is a robust collection of tools and libraries to read, write, and manipulate an image in many image formats including popular formats like TIFF, JPEG, PNG, PDF, PhotoCD, and GIF. With ImageMagick you can create images dynamically, making it suitable for Web applications. You can also resize, rotate, sharpen, color reduce, or add special effects to an image or image sequence and save your completed work in the same or differing image format. Image processing operations are available from the command line, as well as through C, C++, Perl, or Java programming interfaces.
Keywords: ImageMagick,PerlMagick,GraphicsMagick,Magick++,Image,Magick,Magic,Pixel,Graphics,Perl,Wand

I received the following message, "?????? delegation failed ...". What does it mean? How can I improve the appearance of 24-bit images displayed on my colormapped X server? How do I set the transparency index in a GIF image so it displays properly within Mozilla? How can I stop the filenames from changing in the title bar of the animate(1) image window? The image grabbed by import(1) does not look like the image on my X server. What's wrong How do I animate a digital YUV image sequence? How do I view only the red channel of an RGB image? How do I change the default PostScript page size? When I display or convert an image, I get Memory allocation error. What can I do? How do I concatenate three images left-to-right with no borders, frames, or text? How do I create a GIF animation sequence to display within Netscape? When I display a PostScript image it appears to be trimmed. I would like to display the entire page, including any white space. What are visual image directories? How do I use them? I have an HP. How do I take advantage of the Color Recovery option? I use the window ID reported by xwininfo(1) with import and it does include the window manager frame as expected. How can I save the window with its frame? I displayed an image and it appears as one solid color. What did I do wrong? I received the following message, "???? library is not available ...". What does it mean? I want to inspect the values of the matte channel within my image. How can I do that? Convert in.gif out.png" says "Invalid Parameter - out.png" How can I add one of those cool bevels to my image that I see used on the Web? I try to launch display from my window manager and it fails. What's up? When I convert Postscript to another format, how can I improve the appearance of the text? How can I annotate an image with text that is 2 to 3 inches tall? How can I convert my GIF animation sequence to individual image files? How can I remove the background that prints around my image when I display it with Netscape? How do I create a GIF or PNG image with Web safe colors? How come Adobe Acrobat 2.1 can't read ImageMagick's PDF format? How can I add a matte layer to my image? How can I draw with text using 'convert' under Windows NT? Why are my GIF files larger than expected? Why are my JPEG files larger than expected? How do I extract a single image from a multi-image file? How do I make a blank image? What happened to the "combine" utility? 1. I received the following message, "?????? delegation failed ...". What does it mean? ImageMagick uses several freely available packages to perform the translation of certain image formats (PostScript, MPEG, etc.). Make sure these packages are available as described in the README file. Also verify that you have plenty of temporary disk space. If not, set the TMPDIR environment variable to an area where space is available. Finally, for PostScript, verify that Ghostscript supports the pnmraw or ppmraw device (`gs -h`) and that the document contains valid PostScript statements (`gs image.ps`). 2. How can I improve the appearance of 24-bit images displayed on my colormapped X server? If you have a colormapped X server, the number of unique colors in an image must first be reduced to match the requirements of your server before it can be displayed. Display tries to make the color reduced image closely resemble the original. However, there are some options that may improve the appearance. You can use a private colormap. By default, your image must share colors with existing applications on your X server. The colors in your image may be very different than the shared colors and the results may be visually unsatisfactory. Try
     display -colormap private image.miff
The disadvantage is the annoying colormap loading and unloading as you move your pointer in and out of the image window. The YCbCr colorspace may give better results when color reducing images of people faces. Try
     display -colorspace YCbCr image.miff
If you intend to view an image frequently, reduce the number of colors to match the resolution of your X server once and write to a new image. Then display this new image. For example,
     convert -colors 256 -dither image.jpeg image.miff
     display image.miff
This forces the time-consuming process of color reducing the image to one-time, rather than each time the image is displayed. 3. How do I set the transparency index in a GIF image so it displays properly within Mozilla? Display your GIF image with display. Choose Matte from the Image Edit command menu and identify a pixel that has the transparency color. Press Method and select a matte edit method from a pop-up menu. Choose from these methods:
     point
     replace
     floodfill
The point method changes the matte value of any pixel selected with the pointer until the button is is released. The replace method changes the matte value of any pixel that matches the color of the pixel you select with a button press. Floodfill changes the matte value of any pixel that matches the color of the pixel you select with a button press and is a neighbor. Select your transparent pixel with the pointer and press a button. The image is redisplayed with any transparent pixels recolored to the background color. You can select other pixels or areas to force to transparent. When you are satisfied, press Return. Finally, choose Save from the command menu and write your GIF image to a file. Note that setting transparency works best on a TrueColor or DirectColor visual. If your server only exports colormapped visuals you will need to use a Standard Colormap to set transparency.
     xstdcmap -best
     display -map list image.gif
    choose Matte Edit
    select your transparent pixel then press Return
    choose Save
If you do not have the xstdcmap(1) program, try
     display -visual TrueColor image.gif
4. How can I stop the filenames from changing in the title bar of the animate(1) image window? Animate updates the image file name in the title bar of the image window as each image is displayed from the image sequence. To display just a single name that will not change, use -title:
     animate -title "My Image Sequence" images.
5. The image grabbed by import(1) does not look like the image on my X server. What's wrong? Use the -descend option:
     import -descend image.miff
or set this X resource:
     import.descend: True
By default, import quickly grabs the image from the X server. However, it may not always have the correct colors in some areas. This can happen when a subwindow has a different colormap than its parent. With -descend, import descends the window hierarchy. Descending involves grabbing the image and colormap of each window or subwindow associated with the window you select and compositing it on a blank canvas. This can be significantly slower than just grabbing the top-level window but ensures the correct image. 6. How do I animate a digital YUV image sequence? Suppose your sequence is 72 352x240 frames titled frame0.Y, frame0.U, frame0.V, frame1.Y, frame1.U, etc. Use this command:
     animate -geometry 352x240 -scene 0-71 yuv3:frame%d
7. How do I view only the red channel of an RGB image? Use the -gamma option, for example,
     display -gamma 1.0,0.0,0.0 image.miff
8. How do I change the default PostScript page size? The default dimensions of a PostScript page is 612x792. If you prefer another default, change the page geometries (PSPageGeometry) in magick/image.h and recompile. 9. When I display or convert an image, I get Memory allocation error. What can I do? Memory allocation is a complex topic in ImageMagick and image processing requires a lot of memory. ImageMagick tries to take best advantage of the resources available by optimizing its use of virtual memory. Virtual memory is normally the amount of RAM (Random Access Memory) available to the process plus the amount of free space in the system paging area (known as "swap" under Unix, or a "page file" under Windows). In addition to the RAM and the paging area, ImageMagick is able to expand the amount of virtual memory available by using memory-mapped files which cause the file to be treated as extra memory. A piece of hardware known as the Memory Management Unit (MMU) performs the magic which allows the system paging area and memory-mapped files to be treated as more memory by your system's CPU. Usually when a memory allocation error occurs, it is because the system's paging area is full, or the programs memory (heap) is fragmented badly enough that there is no large-enough block of memory available to satisfy the request. In some cases the operating system may artificially limit the memory available to the program. Failures of small memory allocations are generally considered fatal by ImageMagick. If it is impossible to allocate even a little bit of memory, then there is no point in continuing. When large memory allocations associated with allocating memory for image pixels fail, ImageMagick uses that as a key to know that it should start using memory-mapped temporary files to increase virtual memory. Under Unix and other POSIX-compliant systems, these memory-mapped temporary files are created in either the system default location (e.g. /var/tmp) or the directory set by the TMPDIR environment variable. Under Windows, temporary files are created in the directory set by the TEMP or TMP environment variable. If the temporary file directory is too small, or is itself mapped to the system's paging area (no win!), then ImageMagick will fail to allocate more virtual memory via the temporary file and will return an error. The single biggest factor in how much memory is required by ImageMagick is the QuantumDepth setting when it was compiled. The amount of memory (in bytes) required to store a single image in memory is may be calculated via the equation (QuantumDepth*Rows*Columns*5)/8. As a means of example, the following table shows the amount of memory consumed by a single 1024x768 image using the supported QuantumDepth settings:
QuantumDepth | Virtual Memory
--- | ---
8 | 3MB
16 | 8MB
32 | 15MB
Performing an image processing operation may require that several images be in memory at one time. In the case of animations, hundreds of images may be in memory at one time. ImageMagick is designed to be general purpose. It can display many image storage formats (Monochrome, PseudoColor, or TrueColor) on many different types of X visuals (StaticGray, StaticColor, PseudoColor, GrayScale, DirectColor, or TrueColor). To support all these combinations of image storage formats and X visuals, extra memory is required. Additionally, animate and montage store an entire image sequence in memory. It is recommended that systems used to run ImageMagick have at least 96MB of RAM and 140MB free in their paging area. Systems used to process large images (do the math!) may require considerably more memory to operate efficiently. RAM is typically 1000 times faster than disk, so it is important to keep as much data in RAM as possible (buy lots of RAM). The temporary file area should have plenty of free space. The size of the temporary file area is usually the deciding factor as to whether ImageMagick is able to complete an operation. With sufficient free disk space, ImageMagick is primarily limited by your CPU and operating system's ability to address memory. ImageMagick has been used to process images 20K by 20K pixels in size! 10. How do I concatenate three images left-to-right with no borders, frames, or text? Assume your three images are called `image1.ppm`, `image2.ppm`, and `image3.ppm`. Type
     convert +append image1.ppm image2.ppm \
     image3.ppm side_by_side.miff
To concatenate the images top-to-bottom, use `-append`. For more control over the placement of an image, use composite. First create a matte image and position your images onto the matte. For example,
     convert -size 350x500 xc:black composite.miff
     composite -geometry +0+0 composite.miff image1.gif composite.miff
     composite -geometry +100+0 composite.miff image2.gif composite.miff
     composite -geometry +0+300 composite.miff image3.gif composite.miff
     composite -geometry +0+375 composite.miff image4.gif composite.miff
11. How do I create a GIF animation sequence to display within Netscape? Use convert with the -delay and -page options. The -delay option is used to specify the delay in 1/100ths of a second between the display of each frame of the animation. For example,
     convert -delay 20 frame*.gif animation.gif
You can also declare specific delays for each frame of the image sequence. For example, if the delay was 20, 10, and 5, use
     convert -delay 20 frame1.gif -delay 10 frame2.gif \
     -delay 5 frame3.gif animation.gif
Use -page to specify the left and top locations of the image frame:
     convert frame1.gif -page +50+100 frame2.gif -page +0+100 \
     frame3.gif animation.gif
Finally, if you want the image to loop within Netscape, use -loop:
     convert -loop 50 frame*.gif animation.gif
For further information about GIF animation, see GIF Animation on the WWW. Note, that all the images are composited into a single multi-image GIF animation. If you want a single image produced for each frame, use +adjoin:
     convert +adjoin images.* frames%d.gif
12. When I display a PostScript image it appears to be trimmed. I would like to display the entire page, including any white space. ImageMagick automatically trims any PostScript image as defined by the bounding box. To preempt this behavior, remove the bounding box statement from the Postscrpt or explicitly set the page size. For example,
     display -page letter image.ps
13. What are visual image directories? How do I use them? A visual image directory (VID) is an image that contains thumbnails of one or more images in a file directory. Rather than displaying each individual image at its full resolution, you can browse the visual image directory and choose an image to display. You can create a VID with either of these commands:
     montage *.jpg directory.vid
     convert 'vid:*.jpg' directory.vid
Of course you can substitute any filenames you desire. Montage has many relevant command line options. You can exercise more control over the appearance of the VID than with convert. Next display the directory:
     display directory.vid
Finally browse and select an image to display. Move the pointer to the image and press button 3. You can create the VID directory with this command:
     display 'vid:*.jpg'
You can also select Visual Image... from the File menu of the command widget. Note, that creating a VID is time consuming. Creating them on-the-fly within display may be less convenient than using montage or convert . Also, if you create them with montage. or convert, you can reuse them as often as necessary. Note that a visual image directory is useful for looking at individual frames of an image sequence:
     display vid:movie.mpg
14. I have an HP. How do I take advantage of the Color Recovery option? Type
     display -map list image.miff
If you want to use Color Recovery all the time, put this in your X defaults file:
     display.map: list
Now if you need to turn off Color Recovery temporarily, type
     display +dither image.miff
15. I use the window ID reported by xwininfo(1) with import and it does include the window manager frame as expected. How can I save the window with its frame? By default, xwininfo(1) returns the ID of the window you click on. Use the -frame option to get the reparented window ID:
     xwininfo -frame
You can then use the returned window ID with import:
     import -frame -window ID window.miff
16. I displayed an image and it appears as one solid color. What did I do wrong? A blank image generally means that the image is either corrupt or it has a matte channel and the matte values are all zero. ImageMagick treats a matte value of zero as completely transparent. To determine if this is the problem, try
     display +matte image.miff
17. I received the following message, "???? library is not available ...". What does it mean? ImageMagick requires source libraries not included with the distribution to view or convert certain image formats such as JPEG or TIFF. The above message means you did not compile the required library and link with the ImageMagick utilities. See README for the location of these libraries and compiling instructions. 18. I want to inspect the values of the matte channel within my image. How can I do that? View the matte image as a gray scale image. Suppose you have a TIFF image that has a matte channel and is 640 pixels in width and 480 in height. Type:
     convert image.tiff image.matte
     display -size 640x480 gray:image.matte
19. "Convert in.gif out.png" says "Invalid Parameter - out.png" You have inadvertently run the Microsoft Windows program called convert.exe, rather than the ImageMagick program of the same name. The Windows convert.exe program is used to convert a system boot disk from MS-DOS "FAT" format to NTFS format. As such it can only be used one time in the life of a system. You can rename either the MS convert.exe or the ImageMagick convert.exe revise your PATH to put ImageMagick's convert.exe ahead of MS convert.exe edit your Windows Registry as explained in http://savage.net.au/index.html/Install-convert.html 20. How can I add one of those cool bevels to my image that I see used on the Web? There are four types of ornamental borders you can add to your image with ImageMagick. Each is listed below with the procedure to use them with your image. Surround the image with a border of color: Use `-border` followed by the width and height of the border. Set the color of the border with `-bordercolor`. For example, to surround your image with a red border that is 25 pixels wide on each side, use:
     convert -bordercolor red -border 25x25 image.jpg image.gif
Lighten or darken image edges to create a 3-D effect: Use `-raise` followed by the width of the image edge. For example, to create a raised edge effect of 25 pixels, use:
     convert -raise 25 image.jpg image.gif
Surround the image with an ornamental frame: Use `-frame` followed by the width and height of the frame. Set the color of the border with `-mattecolor`. For example, to surround your image with a gray frame that is 25 pixels wide on each side, use:
     convert -mattecolor gray -frame 25x25 image.jpg image.gif
Surround the image with a raised or sunken bevel: Use `-frame` followed by the width and height of the bevel. Set the color of the border with `-mattecolor`. This is just like the description above except you specify a bevel width that matches the frame width. For example, to surround your image with a gray bevel that is 25 pixels wide on each side, use:
     convert -mattecolor gray -frame 25x25+0+25 image.jpg image.gif
     convert -mattecolor gray -frame 25x25+25+0 image.jpg image.gif
21. I try to launch display from my window manager and it fails. What's up? Display determines if it is executing interactively and behaves differently depending on the result. To convince display you are running in an interactive environment when launching from a window manager, use either of
     display logo:Untitled
     display < /dev/console
22. When I convert Postscript to another format, how can I improve the appearance of the text? Simple. Increase the dots-per-inch when converting and sub-sample:
     convert -density 288 -geometry 25% image.ps image.gif
Change the density to 144 and geometry to 50% if the above command fails due to insufficient memory. Alternatively, see the Ghostscript documentation about using high-quality fonts. The `-density` option increases the number of pixels (or dots) generated by Ghostscript when processing the input postscript file. However as all other images formats are generally displayed on screens which are typically about 72 to 100 dots per inch, the output image will be larger. The -geometry option reduces the large image output of ghostscript image back to a normal 72 dpi resolution (25% of 288 dpi gives 72 dpi) but in the process anti-aliases (or smooths) the fonts and lines of the image so as to remove the jaggies you would otherwise get from a normal postscript to image conversion. 23. How can I annotate an image with text that is 2 to 3 inches tall? If you do not access to a particular named font that is large, try scalable fonts. First see if you have any scalable fonts. Type
     xlsfonts -fn '*-0-0-0-0-*'
Or if you are using display, use the font pattern above within the Font Browser (see Image Edit->Annotate). Next substitute the appropriate resolution. Keep in mind that a scalable font must be fully qualified to work. That is, all 14 fields must be specified. Here is one example where we annotate an image with large Helvetica text:
     convert -font '-*-helvetica-*-*-*--300-300-*-*-*-*-iso8859-1' \
     -fill green -draw 'text 50,300 Magick' image.gif annotated.gif
If you have the FreeType support built into ImageMagick, just increase your pointsize and/or density:
     convert -font Helvetica -pointsize 100 -density 300 ...
24. How can I convert my GIF animation sequence to individual image files? Use the scene embedded file format with convert: `convert animation.gif frame%02d.gif` The resulting image files are titled `frame01.gif`, `frame02.gif`, `frame03.gif`, etc. 25. How can I remove the background that prints around my image when I display it with Netscape? Use the `+page` option of the convert command: `convert +page alpha.gif beta.gif` GIF allows for a page offset relative to some background. The page offset information may have been in your GIF image already or it could have been introduced by ImageMagick. Either way, `+page` removes the unwanted page offset and Netscape should behave as expected. 26. How do I create a GIF or PNG image with Web safe colors? Use the `-map` option of the convert command: `convert -map netscape: alpha.gif beta.gif` Netscape predefines 216 colors for colormapped displays. Use the above command to ensure only these predefined colors are used. Otherwise Netscape dithers your image with varying degrees of image fidelity. 27. How come Adobe Acrobat 2.1 can't read ImageMagick's PDF format? The default PDF compression is Zip. You need Acrobat 3.0 and above to read Zip compressed PDF. Instead use no compression or LZW compression when you create the PDF file: `convert +compress images.tiff image.pdf` 28. How can I add a matte layer to my image? One way is to use a bitmap as your transparency mask First, use the `-matte` option to add an all-opaque opacity channel, then use the `composite` utility to copy the graylevel samples from the mask file into your new opacity channel: `convert image.gif -matte temp.miff` `composite -compose CopyOpacity mask.xbm temp.miff transparent.gif` Note, GIF is limited to one transparent color. If your mask has variable opacity, use a format like MIFF, TIFF, or PNG as your output image format. 29. How can I draw with text using 'convert' under Windows NT? The problem is that NT interprets the command line differently than Unix does, causing the documented command to fail. The following command has been reported to work correctly (all on one line): `convert -font Arial -fill blue -draw "text 10,10 'your text here'" d:\test.tif png:d:\test.png` and here is another example which is reported to work (which relies on Ghostscript's 'gs' program to installed): `convert.exe -pointsize 18 -draw "text 0,0 "This is my text!"" C:\blank.gif c:\text.gif` 30. Why are my GIF files larger than expected? LZW-compression was not enabled when ImageMagick was built. Grab the source and configure with the --enable-lzw option. 31. Why are my JPEG files larger than expected? Your JPEG files may contain embedded "profiles" such as Exif or IPTC, or they may contain uncompressed thumbnails. You can use the +profile "*" commandline option or an equivalent API method to remove them. 32. How do I extract a single image from a multi-image file? Use a square-bracket syntax to indicate which frame or frames you want. For example,
     convert "Image.gif[0]" first.gif
Will extract the first image (scene 0) from a GIF animation. Be sure to surround the file specification with quotation marks, to prevent the shell from interpreting the square brackets. 33. How do I make a blank image? There are several ways of making a blank image:
        convert -size 800x600 xc:"#ddddff" ltblue.ppm
        convert -size 800x600 null:white white.ppm
or, to make a black image whose dimensions are the same as those of an existing image,
        convert in.png -threshold 100% black.ppm
34. There used to be a "combine" utility but it's gone. It was replaced by the "composite" utility. The commandline parameters have been rearranged. "Image manipulation software that works like magick"