24 Bit to 16 Bit this time...

[Alhexx]

Once again, I need your help.
I'm trying to convert a 24 Bit Palette into an 16 Bit Palette. But I've got no success...can anyone help me?

 - Alhexx

[ficedula]

Hmm.

Well, understanding that I'm writing this off the top of my head (ie: could be complete bs ... but I don't think it is ) this is how I'd do it:

var
R,G,B:     Byte;
Src,Dst:   Integer;
begin

R := (Src shr 3) and $1F;
G := (Src shr 11) and $1F;
B := (Src shr 19) and $1F;

Dst := (R) or (G shl 5) or (B shl 10);

end;

Takes a 24-bit value in Src, puts a 16-bit value in Dst.

How? Well, first of all extract the colour components R/G/B from the source. Not hard if you know anything about pixel layouts. However: Instead of extracting the top 8 bits, we shift 3 bits more than normal (3/11/19 instead of 0/8/16) and extract 5 bits ($1F = 11111 in binary) into each colour component.

So, now we've got a 5 bit value in each component. Now we just recombine them into a single 16 (well, 15 bit really) bit value by the standard shift, or methods for combining components.

I emphasise: NOT TESTED! May be wrong! But it should give you the basic idea...

[edited] 68 2001-10-16 22:46

[Alhexx]

Whohoo! Looks kinda...complicated.

Okay, as the last time, I found a way myself...it's was a 'hard birth', like we would say in Germany...

Here's my (VB) Code:

Code: [Select]


Private Function Red24Bit(Bits As Byte) As Integer
  Red24Bit = CInt(CInt(Bits / 255 * 31) * 32 * 32)
End Function

Private Function Green24Bit(Bits As Byte) As Integer
  Green24Bit = CInt(CInt(Bits / 255 * 31) * 32)
End Function

Private Function Blue24Bit(Bits As Byte) As Integer
  Blue24Bit = CInt(Bits / 255 * 31 * 1)
End Function


works, too

 - Alhexx

[ficedula]

Damn .. VB doesn't have bitwise shifts? That's crap. But you already knew that

[Darkness]

thank god im learning c++. i havent touched VB in months. The school classes go a bit slow though......

[Alhexx]

Well, it has. Otherwise I wouldn't be able to convert 24Bit into 16Bit. But, as you see above, there's no need to use Bitshifts here.

Darkness: Yep, that's a better choice than VB !

 - Alhexx