ImageMagick Frequently Asked Questions

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 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.

      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

      display -visual TrueColor image.gif

      animate -title "My Image Sequence" images.

      import -descend image.miff

      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 guarentees the correct image.

      animate -geometry 352x240 -scene 0-71 yuv3:frame%d

      display -gamma 1.0,0.0,0.0 image.miff

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. In fact, each image requires 6 bytes per pixel to store in memory. Additionally, animate and montage store an entire image sequence in memory.

For animation, consider using the MPEG programs from Berkeley if you encounter memory limitations with animate. It only stores a few frames at a time in memory. Convert has an option to create the proper CCIR 601 2:1:1 files as input to the MPEG program. However, the CCIR 601 2:1:1 image format is lossy. Computer generated images may not look very good.

      montage +frame +shadow +label  +geometry -tile 3x1 \
          image1.ppm image2.ppm image3.ppm concatenated.ppm

For more control over the placement of an image, use combine. First create a matte image and position your images onto the matte. For example,

      convert -size 350x500 xc:black composite.miff
      combine -geometry +0+0   image1.gif composite.miff composite.miff
      combine -geometry +100+0 image2.gif composite.miff composite.miff
      combine -geometry +0+300 image3.gif composite.miff composite.miff
      combine -geometry +0+375 image4.gif composite.miff composite.miff

      display -page letter image.ps

      montage *.jpg directory.vid
      convert 'vid:*.jpg' directory.vid

Of course you can substitute any filenames you desire. Montage has many relevant command line option. 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

      display -map list image.miff

      display.map: list

Now if you need to turn off Color Recovery temporarily, type

      display +dither image.miff

      xwininfo -frame

      import -frame -window ID window.miff

      display +matte image.miff

      cd ImageMagick
      rm magick/decode.o magick/encode.o
      make

      convert image.tiff image.matte
      display -size 640x480 gray:image.matte