| Re: device, true_color=24, decompose=0 [message #15781] |
Mon, 14 June 1999 00:00 |
Liam Gumley
Messages: 473
Registered: November 1994
|
Senior Member |
|
|
Gary Fu wrote:
> Based on the IDL documentation the "decomposed=0" for the "device"
> command allows users with TureColor displays to use IDL programs written
> for standard, PseudoColor displays without modification. But I don't
> understand why I got
> different results in the following two idl codes:
>
> device, pseudo=8
> window, xsize=100, ysize=100
> erase, 50
> print, min(tvrd()) ; print out 50
> tvlct, 100, 100, 100, 50
> erase, 50
> print, min(tvrd()) ; print out 50
>
> ****************************************************
>
> device, true_color=24, decompose=0
> window, xsize=100, ysize=100
> erase, 50
> print, min(tvrd()) ; print out 50
> tvlct, 100, 100, 100, 50
> erase, 50
> print, min(tvrd()) ; print out 100
The IDL 5.2 online book 'Using IDL', section 'Displaying Images',
subsection 'True Color Displays' explains how TVRD works differently in
True Color mode:
"Furthermore, if the same image is loaded into each channel, operation
of the display mimics that of a standard 8-bit deep pseudo-color
display. Most, but not all, IDL image processing procedures written for
a standard color display will run on a true-color display without
modification. The routines that transfer images to the display, TV and
TVSCL, write the same 8-bit data to each channel (channel 0) if no
channel parameter is present. The function TVRD, which reads data from
the display, returns the maximum value contained in the three-color
channels for each pixel if no channel parameter is present."
Thus in True Color mode, TVRD does not return the byte pixel values as
it does in 8 bit mode. To see this effect more clearly, try running the
example shown below, which prints both the color table values (from
TVLCT), and the pixel values (from TVRD):
;---cut here---
PRO TEST
;- Default color table
loadct,0
erase,50
tvlct,r,g,b,/get
print,'Red color table entry = ',r[50]
print,'Minimum pixel value = ',min(tvrd())
;- Modify color table entry 50
tvlct,100,100,100,50
erase,50
tvlct,r,g,b,/get
print,'Red color table entry = ',r[50]
print,'Minimum pixel value = ',min(tvrd())
END
;---cut here---
Here's what I get running on an SGI 24 bit console:
% idl
IDL Version 5.1 (IRIX mipseb). Research Systems, Inc.
Installation number: 13221-0.
Licensed for use by: Space Science and Engineering Center, Univ. of
WI-Madison
For basic information, enter "IDLInfo" at the IDL> prompt.
IDL> device,pseudo=8,decomp=0,retain=2
IDL> test
% Compiled module: TEST.
% Compiled module: LOADCT.
% Compiled module: FILEPATH.
% LOADCT: Loading table B-W LINEAR
Red color table entry = 89
Minimum pixel value = 50
Red color table entry = 100
Minimum pixel value = 50
IDL> help,/device
Available graphics_devices: CGM HP LJ NULL PCL PRINTER PS REGIS TEK X Z
Current graphics device: X
Server: X11.0, Silicon Graphics, Release 6001
Display Depth, Size: 8 bits, (1280,1024)
Visual Class: PseudoColor (3)
Bits Per RGB: 8
Physical Color Map Entries (Used / Total): 143 / 256
Colormap: Shared, 143 colors. Translation table: Enabled
Graphics pixels: Combined, Dither Method: Ordered
Write Mask: 255 (decimal) ff (hex)
Graphics Function: 3 (copy)
Current Font: <default>, Current TrueType Font: <default>
Default Backing Store: Pixmap.
Window Status: ---------------------
id typ( x, y, backing store) id typ( x, y, backing
store)
0: Win( 640, 512, Pixmap)
IDL> exit
% idl
IDL Version 5.1 (IRIX mipseb). Research Systems, Inc.
Installation number: 13221-0.
Licensed for use by: Space Science and Engineering Center, Univ. of
WI-Madison
For basic information, enter "IDLInfo" at the IDL> prompt.
IDL> device,true=24,decomp=0,retain=2
IDL> test
% Compiled module: TEST.
% Compiled module: LOADCT.
% Compiled module: FILEPATH.
% LOADCT: Loading table B-W LINEAR
Red color table entry = 50
Minimum pixel value = 50
Red color table entry = 100
Minimum pixel value = 100
IDL> help,/device
Available graphics_devices: CGM HP LJ NULL PCL PRINTER PS REGIS TEK X Z
Current graphics device: X
Server: X11.0, Silicon Graphics, Release 6001
Display Depth, Size: 24 bits, (1280,1024)
Visual Class: TrueColor (4)
Bits Per RGB: 8
Physical Color Map Entries (Used / Total): 256 / 256
Colormap: Private, 16777216 colors. Translation table: Bypassed
Graphics pixels: Combined, Dither Method: Ordered
Write Mask: 16777215 (decimal) ffffff (hex)
Graphics Function: 3 (copy)
Current Font: <default>, Current TrueType Font: <default>
Default Backing Store: Pixmap.
Window Status: ---------------------
id typ( x, y, backing store) id typ( x, y, backing
store)
0: Win( 640, 512, Pixmap)
IDL> exit
Cheers,
Liam.
--
Liam E. Gumley
Space Science and Engineering Center, UW-Madison
http://cimss.ssec.wisc.edu/~gumley
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
