Size of texture on Video memory

Scruples

In my search for the answer to how large a dxt1 compressed 1024x1024 texture was in video memory, I found the answer (512kb) and some basic math's. But because I don't want to break out the calculator every time I want to know the size a texture will end up in memory I thought it best if I take 5 minutes to commit a few sizes to...memory .

Please correct me if I am wrong.

Uncompressed
1024x1024 4MB
2048x2048 16MB

Dxt1
1024x1024 512kb
2048x2048 2MB

Dxt5
1024x1024 1MB
2048x2048 4MB

I assume mip-mapping isn't calculated already so all these values would have another 50% ontop if they have mips.
Knowing the size of 3dc/BC5 would be useful too, the wiki page was confusing for that one.

JamesWild

Might also want to note that a 4Mb 1024x1024 is RGBA (has alpha) without alpha it's 3Mb. (8-bit)

According to the wiki, 2:1 compression ratio from an 8-bit source, so 1.5Mb for a 1024x1024 3DC? (as I doubt the source normal maps have an alpha channel) Multiply by 4 for double the size, so 6Mb for 2048x2048 3DC.

Ashaman73

JamesWild wrote: »

Might also want to note that a 4Mb 1024x1024 is RGBA (has alpha) without alpha it's 3Mb. (8-bit)

With padding it is most likely still 4MB (memory access).

You need to consider mipmaps to, therefore
2048^2 = 16 MB + 4MB + 1MB + 0.25MB ~= 21 MB

Not everything is hold in real videomemory, parts are in the system memory which will be uploaded on demand.

JamesWild

Yeah mipmaps were noted in the first post... thanks for the further input. Forgot that most implementations use padding for the RGB format.

Ashaman73

Opps, you're right :-)

cupsster

How much memory does my texture take up?
Compression Memory consumption
RGB Compressed DXT1 0.5 bpp (bytes/pixel)
RGBA Compressed DXT5 1 bpp
RGB 16bit 2 bpp
RGB 24bit 3 bpp
Alpha 8bit 1 bpp
RGBA 16bit 2 bpp
RGBA 32bit 4 bpp
To figure out total texture size: width * height * bpp. Add 33% if you have Mipmaps.