Screen Capture Tools for IDL

by Liam E. Gumley

SAVEIMAGE ( Version 1.17, 8 February 2000. IDL 5.0 or higher required)
Save the contents of the current graphics window to a GIF, BMP, PICT, TIFF, or JPEG format output file, e.g.

IDL> saveimage, 'test.gif'
IDL> saveimage, 'test.jpg', /jpeg

SHOWIMAGE (Version 1.15, 19 November 1999. IDL 5.2 or higher required)
Display an image in GIF, BMP, PICT, TIFF, or JPEG format (the format is detected automatically), e.g.

IDL> showimage, 'test.gif'

Both procedures work transparently in either 8-bit (256 color), 16-bit (65,536 color), or 24-bit (16,777,216 color) display mode.

I was tired of the usual process involved in saving the contents of the current graphics window to an image file (GIF or JPEG for example). These days IDL users are just as likely to have a 24-bit display as an 8-bit display, and thus you run into cases where a 24-bit image is displayed on-screen, but you want to save it as an 8-bit image (e.g. GIF). Likewise, there are times when an 8-bit image is displayed on-screen, but you want to save it as 24-bit (e.g. JPEG).

To get around all the headaches involved in this process, I wrote the procedure SAVEIMAGE which determines whether you are running IDL in 8, 16, or 24-bit mode, and automatically does any conversions necessary to save the image in the selected format. In addition, I wrote a companion procedure SHOWIMAGE, which reads and displays images in any of the formats supported by SAVEIMAGE, regardless of whether you are running in 8, 16, or 24-bit mode.

Please let me know if you have any questions or comments, especially if you find a bug. SAVEIMAGE and SHOWIMAGE are licensed under the terms of the GNU General Public License (GPL).

Revision History

8 February 2000

• Added CUBE keyword to SAVEIMAGE for better color matching when converting from 24-bit to 8-bit,
• Fixed bug when converting from 8-bit to 24-bit.

21 January 2000

• Added support for Z buffer,
• Now uses decomposed color mode when reading from 24-bit displays.

19 November 1999

• Added GNU General Public License text.

10 September 1999

Both procedures now handle image order correctly (thanks to Ivan Zimine for the tip).

9 September 1999

• 16-bit (65,536 color) mode is now supported by SAVEIMAGE and SHOWIMAGE,
• SHOWIMAGE now displays TrueColor images in 16-bit or 24-bit mode without disturbing the color table,
• SHOWIMAGE now preserves the color decomposition mode.

Liam E. Gumley
Last updated 8 February 2000