What is the meaning of "one-half meter"?

I have found this phrase that as a non-native English speaker perplexes me:

...returning images with a resolution of up to one-half meter per pixel.

The possible meanings of "one-half" to me are:

• Every pixel represents half a meter
• Every pixel represents one and a half (1.5) meters
• Every pixel may represent any possible distance between the minimum of half a meter and the maximum of one meter
• Something entirely different

Can you please explain?

N.B. Is it

one and a half meter

OR

one and a half meters ?

To me (a British English native) the expression is unambiguous in meaning:

0.5 metre per pixel [UK metre = US meter]
i.e. one-half of a metre per pixel

In answer to your N.B., the plural form would be:

one and a half metres (or meters)
1.5 metres (or meters)

Addendum:
Additionally, also note that the resolution is "up to one-half meter per pixel", so the resolution may be less than 0.5m per pixel, but no lower resolution limit is specified.