CGTRANSPARENTIMAGE

CGTRANSPARENTIMAGE
Creates a semi-transparent image for display. Optionally, a "missing"
color or color index (for 2D images) can be set to a completely transparent value.
The transparent image can be saved as a transparent PNG file.

Params

image: in, optional, type=byte
A 2D image or a 24-bit image with or without an alpha channel. If an alpha
channel is present, it will be modified by the program.

Keywords

brewer: in, optional, type=boolean, default=0
This keyword is used only if the `CTIndex` keyword is used to select a color table number.
Setting this keyword allows Brewer color tables to be used.

ctindex: in, optional, type=integer
The index number of a color table. The `Brewer` and `Reverse` keywords will be checked
to see how to load the color table into the `Palette` keyword. This keyword will take
precidence over any colors that are loaded with the `Palette` keyword.

missing_value: in, optional, type=various
The "color" of a pixel that will be treated as a "missing" color or value.
Any pixels in the image with this color value will be set completely
transparent. If `Color` is a string, use cgColor to obtain a color triple.
If `Color` is a non-strint scalar, this value is taken to be the missing color index
in a 2D image. Otherwise, this is assumed to be a color triple that indicates
the "missing" color or value in the output image. The alpha channel in the output image
is set to 0 for the "missing" color, which makes this value completely transparent.

filename: in, optional, type=string
The name of an image file that can be read with READ_IMAGE. Used to
select the input image if the `image` parameter is not used.

nogui: in, optional, type=boolean, default=0
Set this keyword if you do not wish to have the user confirm the name of
the output PNG file selected with the `PNGFile` keyword.

palette: in, optional, type=byte
Set this keyword to a 3x256 or 256x3 byte array containing the RGB color
vectors to be loaded before the transparent image is created. Such vectors can be
obtained, for example, from cgLoadCT with the RGB_TABLE keyword::

IDL> cgLoadCT, 4, /BREWER, /REVERSE, RGB_TABLE=palette
IDL> tImage = cgTransparentImage( cgDemoData(7), PALETTE=palette)

The default is to use whatever colors are loaded in the current hardware color table.
A palette applies only to 2D input images.

pngfile: in, optional
If this keyword is set, the output image is written as a transparent
PNG file in 4xMxN format. Optionally, this keyword can be set to the
name of the output PNG file. The user will have the option of confirming
the name of the output file, unless the `NoGUI` keyword is set.

reverse: in, optional, type=boolean, default=0
Set this keyword to reverse the color table vectors selected with the `CTIndex` keyword.
transparent: in, optional, type=integer, default=50
The percentage of transparency desired in the output image. A number
between 0 and 100.

wset: in, optional, type=long
If image parameter is not present, make the window indicated with
this keyword the current graphics window for obtaining an image parameter.
If not passed, and no image is present, then the current graphics window is
used to create the image.

Examples

cgDisplay, WID=0
cgImage, cgDemoData(5), CTIndex=0, /Interp
timage = cgTransparentImage(MISSING_VALUE='black', TRANSPARENT=50)
cgDisplay, WID=1
cgImage, cgDemoData(7), CTIndex=22
cgImage, timage

Author

FANNING SOFTWARE CONSULTING::
David W. Fanning
1645 Sheely Drive
Fort Collins, CO 80526 USA
Phone: 970-221-0438
E-mail: david@idlcoyote.com
Coyote's Guide to IDL Programming: http://www.idlcoyote.com

History

Change History::
Written, 23 October 2012 to replace Make_Transparent_Image, which was retired. DWF.

Library	Coyote

Version	July-2015