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How are 16-bit bitmaps saved, 555 or 565?


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#1 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 05 November 1999 - 05:58 PM

I sent Lord Necron an e-mail about this question a few hours ago, but since I am so impatient I'll post here too!

I understand the structure of bitmaps including bits per pixel and how 8/16/24/32 RGB values are mapped. But my question is this... if you have 8,24, or 32 bpp you know exactly how a Windows bitmap is stored on disk, 1 byte per pixel (palette index), 3 bytes per pixel (BGR), and 4 bytes per pixel (ABGR, i think), respectively. But how are 16 bpp bitmaps stored on disk??? is it 2 bytes as in 1555 or is it 565??? Or are all bitmaps in 1555 format? Is there part of the information header or file header that tells you how it is stored? If anyone out there knows let's hear the answer. Thanks!


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#2 NuFAN   Members   -  Reputation: 122

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Posted 05 November 1999 - 02:35 AM

Simply count the colors in the bitmap. If it uses 555, then there are about 32.000 used. If there are 65k colors used, it must be 565 or 4444. Mostly, 565 is used but there are also formats that use 4444. Just look at the file specs on www.wotsit.org and you'll have it.

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#3 Niels   Members   -  Reputation: 122

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Posted 05 November 1999 - 11:24 AM

Eh! Doesn't that pretty much depend on who/what stored the file? Nothing is really given unless you're referring to a specifc format (neither in 16, nor in 32 or 24 bit - the latter two can be both RGBA, ARGB, ABGR or whatever + various compression schemes).

I can't immediately think of any format that stores in 16-bit (But then again, I'm a sucker for 32-bit tga and JPEG, so I'm a lousy source on that subject )

Personally I would store raw 16-bit data in 565 if I absolutely had to. 1555 if transparency was required. If the data was already in say, 555, I wouldn't bother converting it though.

/Niels


#4 Splat   Members   -  Reputation: 122

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Posted 05 November 1999 - 05:48 PM

Most applications don't output in 16-bit format. However, I generally do all my graphics in 24-bit mode (or 32 with 8 bit alpha), then if I need to be in 16-bit mode I convert the 24-bit source images in the game using a dithering algorithm to whatever 16-bit format is required. Flexible, and allows for the highest quality images without needing more than one copy of each graphic file (for different pixel formats)

- Splat

[This message has been edited by Splat (edited November 05, 1999).]


#5 evaclear   Members   -  Reputation: 162

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Posted 05 November 1999 - 05:58 PM

actualy I believe the bitmap standard states that all 16 bit bitmaps will be saved as 5-5-5.




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