File format Format in which to save the image. See Custom format below
for details on creating files in a customized format).
Save entire image/selected region - If ``entire image'' is selected, the currently-selected image will
be saved in its entirety. Otherwise, only the currently-selected
screen region (which can beyond an image or contain 2 or more
images) will be saved. The actual size of the region saved is
displayed after the file is written.
Bits/pixel -
Select a standard depth of 1,8,15,16,24, or 32 bits/pixel, or select ``other'' to specify any other value between 1 and 32. The resulting file size will be proportional to the bits/pixel. Saving an image in a lower bits/pixel than it was created can cause a loss in color accuracy. For example, if an 8-bit image is saved as a 3 bit/pixel image file, the colors in the image will appear slightly different from the original colors. If it is saved as a monochrome (1 bit/pixel) image, all pixels above 50% of the maximum color will appear white and those below 50% of maximum will appear black.
NOTE - Some file formats (e.g., GIF and PCX) only allow certain values for bits/pixel and number of colors. Imal displays an error message if an illegal value is selected.
WARNING - Due to limitations in the capabilities of some other programs, saving images using ``non-standard'' bits/pixel or using ``non-standard'' numbers of colors can result in image files that are not readable by some other image viewers. For example, one well-known shareware file interconversion program can only handle 4,8, and 24 bit/pixel TIFF images, but not the common 15, 16, or 32 bit images. One commercial Macintosh program can only handle 8,15,24, or 32 bit/pixel images, but not 16 bits/pixel. Very few other programs can handle odd values such as 12 bits/pixel. However, these values can be extremely useful and widely used in handling radiological, electron microscope, or MRI images, which are often of unusual pixel depths.
Imal will display an appropriate warning if a ``non-standard'' file format is selected.
Treat data as Color / Gray scale -
When saving images greater than 8 bits per pixel as TIFF or Custom files, it is sometimes useful to save the image as if the image data represent shades of gray instead of colors. Selecting ``gray scale'' causes imal to treat the image as if each pixel value was already a ``luminosity'', and skips the conversion from RGB to luminosity. This setting is ignored if the image is saved as 8 or less bits/pixel, or if it is saved as a color image (by selecting ``2'' or ``3'' as the number of primary colors). Normally, this setting should be kept on ``Color''.
Filename - The file name under which the image will be saved (can include
drive and path).
Image no. - Indicates the currently-selected image which will be saved if
``save entire image'' is checked. Has no effect if ``selected region''
is checked. This option is mainly for informative purposes and does
not normally need to be changed.
Extra TIFF Param.(for `Other') - For TIFF and custom file formats, it is also possible to customize several
additional parameters.
No.of primary colors(1-4) -
If 1 primary color is selected, the image will be converted to grayscale
before saving, and the red, green, blue, and black bits/pixel will be
ignored. If more than 1 color is specified, the number of bits for each
color, when added together, must equal the total number of bits/pixel
specified under ``other bits/pixel''.
For example, to save only 4 bits each of the red and blue planes of an image,
set the following values:
NOTE: Imal cannot display more than 8 bits/pixel
of each color (i.e., a total of 24 bits/pixel). This is due mainly to
limitations in the current generation of video cards. Thus, there is no advantage
in setting the bits/pixel for any one color higher than ``8''.
Black bits/pixel can only be specified if the ``cmyk'' option is
checked.
RGB to CMYK - Converts the image from RGB to CMYK (cyan, magenta, yellow & black) format
when saving. (CMYK images are automatically converted to RGB for display, since
there cannot be a ``CMYK computer monitor''). For non-standard bits/pixel
modes, it is also necessary to specify the number of red/cyan, green/magenta,
blue/yellow, and black bits/pixel. If a non-standard format is selected, imal
will display a warning to that effect. Selecting CMYK is only allowed for the
32 bit/ pixel standard mode and the ``Other'' (non-standard) mode. Attempting to
save an image with CMYK checked in any other mode will produce an error. This
is done to ensure consistency with the TIFF specification which (as of version
6.0) does not recommend using lower color depths for CMYK.
This option is useful for exporting the image to other programs which cannot create their own CMYK images for printing.
JPEG quality factor - An integer between 1 and 99. Values above 90 or below 10 are not recommended.
Smaller values result in greater compression and more signal loss. A quality
factor of 100 would require arithmetic compression and is not supported because
of patent considerations.
NOTE: JPEG is a lossy file format. This means an image saved in JPEG format will lose some information. Images consisting of text and sharp lines are not good candidates for Jpeg compression, because the compression algorithm is optimized for realistic scenes such as images from photographs. Files should only be saved in Jpeg format when all image processing has been completed, and the smallest possible size is needed. JPEG is the most suitable format for images on Web pages.
Some settings, such as red, green, blue, and black bits/pixel, and CMYK conversion, are ignored for JPEG.
Animated and multiframe images
Animated images can be saved in GIF89a or custom formats. Using any other format creates an error message.
Multiframe image format consists of a one-line text header containing the following, separated by whitespace:
Image files can be post-processed by any other program after being written by imal. This program must be able to receive data from stdin and send its output to a specified file (e.g., gzip -f ). The extension specified in the ``Save Image'' dialog will be added to the filename.
Typically, the use of this would be to compress the image file, but it could also encrypt it or perform some other action on it. The advantage of using an external program to compress image files is that, should a more efficient compression algorithm come along, the new program can be substituted without invalidating the image file format. Also, file formats such as FITS, which have no compression, can be easily stored in compressed form using this feature.
The Post-Processing command is automatically deselected if the original image was not processed by the corresponding decompression program.