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jamesastro
Inspiring
June 8, 2021
Answered

Confused by AE 16-bit RGB colors values

  • June 8, 2021
  • 1 reply
  • 1130 views

Hi Everybody,

 

I'm writing a Mac AE plugin, and I'm trying to convert a 16-bit EffectWorld into an image that can be used by the Mac OS APIs. While doing this, I noticed a peculiar thing about 16-bit EffectWorlds: The RGB components of each pixel color range in value from 0-32768, rather than 0-65535 like I was expecting. They behave more like 15-bit colors rather than 16-bit.

 

For example, solid red is represented by these color components:

• Red = 32768

• Green = 0

• Blue = 0

 

Does anyone know why this is? It just seems like an odd choice, and it gives AE fewer colors to work with.

This topic has been closed for replies.
Correct answer fnordware

It's true! This is Adobe 16-bit, which maxxes out at 0x8000 instead of 0xffff, so it's more like 15-bit plus 1. The reason they did this is so you use x >> 15 to divide by PF_MAX_CHAN16. Nobody else does this, so you'll have to convert to real 16-bit to work with other libraries. I do it this way:

 

#define PF_MAX_CHAN16			32768
#define PF_HALF_CHAN16			16384

static inline uint16_t Promote(uint16_t val)
{
	return (val > PF_HALF_CHAN16 ? ( (val - 1) << 1 ) + 1 : val << 1);
}

static inline uint16_t Demote(uint16_t val)
{
	return (val > PF_MAX_CHAN16 ? ( (val - 1) >> 1 ) + 1 : val >> 1);
}

 

1 reply

F
fnordwareCorrect answer
Inspiring
June 8, 2021

It's true! This is Adobe 16-bit, which maxxes out at 0x8000 instead of 0xffff, so it's more like 15-bit plus 1. The reason they did this is so you use x >> 15 to divide by PF_MAX_CHAN16. Nobody else does this, so you'll have to convert to real 16-bit to work with other libraries. I do it this way:

 

#define PF_MAX_CHAN16			32768
#define PF_HALF_CHAN16			16384

static inline uint16_t Promote(uint16_t val)
{
	return (val > PF_HALF_CHAN16 ? ( (val - 1) << 1 ) + 1 : val << 1);
}

static inline uint16_t Demote(uint16_t val)
{
	return (val > PF_MAX_CHAN16 ? ( (val - 1) >> 1 ) + 1 : val >> 1);
}

 

J
jamesastroAuthor
Inspiring
June 8, 2021

Thanks for the quick reply. That's exactly what I needed.  🙂

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