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William Leue
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Joined: 03/07/2020
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Posted: 06:15pm 14 Jul 2021

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I am trying to figure out how to decompose a given color into its RGB components. The documentation is some help but I seem to be missing something.

For instance, in 8-bit mode, the documentation on the MODE command says that each pixel consists of an 8-bit byte, divided into two 3-bit fields for R and G, and the remaining 2-bit field for B.

So for instance, take the color white, which we know can be generated using rgb(255, 255, 255) or just rgb(white). If we assign this value to a normal 64-bit integer we get &HFFFFFFFF, as expected. Limiting this to just the least significant 8 bits we have &HFF.

My mental model says that each of the RGB field needs to be interpreted as equal to 255. (Of course this model is likely wrong.) But if the model is right, I can't figure out how those bitfields end up as 255's. Even shifting them to the most significant bits of an 8-bit value doesn't do it.

So I'm hoping that one of our gurus can help me grok this.
Thanks!
-Bill

William Leue
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Joined: 03/07/2020
Location: United States
Posts: 405

Posted: 06:17pm 14 Jul 2021

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Of course I meant to say, "Given the hex value of a color and the current color bit depth, how do I decompose that into RGB values?"

-Bill

thwill

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Joined: 16/09/2019
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Posted: 06:20pm 14 Jul 2021

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Not sure if it's significant, but Hex$(RGB(White)) and Hex$(RGB(255,255,255)) give FFFFFFF (7 x F), not the 8 x F that you report.

Best wishes,

Tom

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William Leue
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Posted: 06:22pm 14 Jul 2021

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Tom said,

Quote Not sure if it's significant, but Hex$(RGB(White)) and Hex$(RGB(255,255,255)) give FFFFFFF (7 x F), not the 8 x F that you report.

Yup, you are right, Tom. For this example it's not important.

-Bill

lizby
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Joined: 17/05/2016
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Posts: 3378

Posted: 08:10pm 14 Jul 2021

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This thread might help, though it's 16-bit, not 8-bit.
Edited 2021-07-15 06:12 by lizby

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William Leue
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Joined: 03/07/2020
Location: United States
Posts: 405

Posted: 08:13pm 14 Jul 2021

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Thanks lizby, that is quite helpful!
-Bill

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