Multiplexed array will have the same brightness, each On LED is given the same current pulse for the same time as any other LED, so the eye/brain percieves them as all being on the same brightness. That's the beauty of persistence of vision (POV).
So 32 columns, each one is on 1/32 of the time, 1042uS each column, for 30 Hz refresh rate, flicker free. Use SPI.transfer( ) and blink without delay to pull data from a 128 byte array.