topic Index Colors and CTB in AutoCAD Forum

Index Colors and CTB

Anonymous — Mon, 15 Apr 2019 11:07:51 GMT

Some of index colors ie 9 of them have a name and Number.

Colors Red 255,0,0, Yellow 255,255,0 and Green 0,255,0 have Number 1 ,2 and 3.

But these have even number 10, 50 and 90.

So my question is why these 9 colors are special?

Sometimes we recieve CTB files from the customer and what I can see is that color Red is converted differently depended on if it is set as 1, 10 or Red and it can be tricky.

Re: Index Colors and CTB

BrianBenton — Mon, 15 Apr 2019 11:17:25 GMT

These were the original colors in AutoCAD. They had names and number. Once the amount of colors expanded, Autodesk did not name all 255 colors, they just stayed with the numbers.

Re: Index Colors and CTB

rkmcswain — Mon, 15 Apr 2019 12:14:49 GMT

What @BrianBenton said, and I must add that color 1 (red) is NOT the same as 255,0,0; and this goes for all of the ACI colors (colors 1-255), because ACI colors can be manipulated with a plot style table to print with varying colors and lineweights, while the truecolors (e.g.: 255,0,0) will always print as the color they appear on screen, plot style tables have no effect on these.

Re: Index Colors and CTB

Anonymous — Mon, 15 Apr 2019 14:38:21 GMT

Yes! This is my understanding too!

When I say that Index colors as Color 1/Red and color 10 are the same I mean they are both 255,0,0 as True Color!

Using a certain CTB replacing all colors with black when I want to print Red as Red I just use 255,0,0 as True Color and CTB would not change it!

The CTB I attached here effects color 1=RED and Color 10 diffrently but both are actually red or 255,0,0 as True Color!

So I was surprised by this behavior of changing both to black but with diffrent Lineweight!

Re: Index Colors and CTB

dgorsman — Mon, 15 Apr 2019 15:40:32 GMT

ACI colors 1 and 10 are not both "RED" - that is an equality you are imposing. Even though they have the same RGB/TrueColor equivalents, 1 != 10. The name "RED" refers only to ACI color 1. ACI color 1 is the same as "RED" but ACI color 10 is not. CTB files have no lookup data for RGB/TrueColor values, so there is no literal equivalence in the way you are thinking.

Yes, I know - this is a *very* literal interpretation of the situation. But that is sometimes necessary when dealing with hard data.

Re: Index Colors and CTB

s.borello — Mon, 15 Apr 2019 19:23:58 GMT

Some of those color numbers represent true colors... they will take precedence over any plot styles you may be using.

Re: Index Colors and CTB

Anonymous — Wed, 17 Apr 2019 10:03:18 GMT

Please explain!

Re: Index Colors and CTB

BrianBenton — Wed, 17 Apr 2019 11:44:56 GMT

Setting a layer/object to a TRUE COLOR will override the plot style and will print the object as the true color's color.

Re: Index Colors and CTB

Anonymous — Wed, 17 Apr 2019 12:06:13 GMT

Yes! This is how I do it!

Happy Easter to everybody!

Re: Index Colors and CTB

rkmcswain — Wed, 17 Apr 2019 12:18:33 GMT

@Anonymous wrote:

Please explain!

It has been, see post #3 in this thread.