Image Width Limits on Macs?

[Martin Baxter]

Geoff Canyon wrote:
> The docs say:
> 
>     Cross-platform note:  On Mac OS and OS X systems, the
>     maximum width of an image is 16384 divided by the
>     screen's bit depth. (For example, if the number of colors
>     is "Millions", the maximum image width is 4096 pixels.)
> 
> First, how do you divide 16384 by 4096 you get 4. How is 4 related to 
> "Millions?"
> 
> Second, any idea what the other options are?
> 
> Now that I think about it, could it mean _byte_ depth? It takes 4 bytes 
> to store a pixel in millions of colors. So then thousands would be 2, 
> correct? and anything less than thousands 1?
> 
> Any help much appreciated, as my bug-free code example has a bug until 
> this is resolved ;-)

You pretty much have it I think Geoff. I don't know if bit depth is a
correct term here or not, it sounds technically incorrect to me, since
the concept is byte-based. It may be one of those "casual usages".

Commonly, a pixel uses 4 bytes, one each for red,green,blue and one for
alpha data. R,G and B having 256 values each multiply to give 16,777,216
possibilities according to my steam-driven calculator, hence "millions"
of colours. Thousands would be 2 bytes 256*256=65536 quite correct, and 
one-byte, usually called "8 bit" colour is an arbitrary set of up to 256 
colours referenced by a look up table with 256 entries.

Martin Baxter