Posted by
Cammer, Michael on
Jun 20, 2016; 5:58pm
URL: http://imagej.273.s1.nabble.com/What-colour-is-RGB-black-tp5016697p5016698.html
Take a look at this based on
https://imagej.nih.gov/ij/macros/tools/ColorPickerTool.txt found in the getPixel(x, y) command at
https://imagej.nih.gov/ij/developer/macro/functions.html#G.
Regardless, I do find it strange that when making a new image as black or expanding the canvas without specifying zero is a different zero value (looks like #FFFFFF which I would expect to be white) than when specifying the value as zero.
newImage("Untitled1", "RGB black", 128, 128, 1); run("Canvas Size...", "width=150 height=150 position=Center"); print(getPixel(0,0)+" \t"+ getPixel(128,128)); // close();
newImage("Untitled2", "RGB black", 128, 128, 1); run("Canvas Size...", "width=150 height=150 position=Center zero"); print(getPixel(0,0)+" \t"+ getPixel(128,128));
v = getPixel(128,128);
if (bitDepth==24) {
red = (v>>16)&0xff; // extract red byte (bits 23-17)
green = (v>>8)&0xff; // extract green byte (bits 15-8)
blue = v&0xff; // extract blue byte (bits 7-0)
print(red+ " \t " + green + " \t "+ blue);
} else
=========================================================================
Michael Cammer, Microscopy Core & Skirball Institute, NYU Langone Medical Center
Cell: 914-309-3270 Office: Skirball 2nd Floor main office, back right a.k.a. The Coldroom
http://ocs.med.nyu.edu/microscopy &
http://microscopynotes.com/-----Original Message-----
From: ImageJ Interest Group [mailto:
[hidden email]] On Behalf Of Gabriel Landini
Sent: Monday, June 20, 2016 11:36 AM
To:
[hidden email]
Subject: What colour is RGB black?
I should know this... but when I resize a canvas, I get a different value for black, even if inspecting the pixels shows (000,000,000) when I use the "zero"
parameter.
.
Running the macro below with the background set in the colour picker set to white for the foreground and black for the background I get these two values for the background pixel at (0,0) :
-16777216
0
newImage("Untitled", "RGB white", 128, 128, 1); run("Canvas Size...", "width=150 height=150 position=Center"); print(getPixel(0,0)); close();
newImage("Untitled", "RGB white", 128, 128, 1); run("Canvas Size...", "width=150 height=150 position=Center zero"); print(getPixel(0,0));
I guess that it has to do with the representation of the RGB triplet, but I am most puzzled about it since they both are the same colour (or so I though!).
Cheers
Gabriel
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