Hi there,
I’m working for the first time with hi density leds (144led/m neopixels).
With fast animations all is good, but with slow moves it doesn’t look very well 
I really see the pixels going on and off, so with the diffuser it seems to flash.
I’ve tried using @Mark_Kriegsman 's anti-aliasing algorithm but that doesn’t change much.
Any ideas on how to get this flashing removed ?
Sorry, the flashing doesn’t appear well on the video but I really see it through my eyes 
Controller : Teensy 3.1
Branch : FastLED 2.1
3 strips of different lengths connected to 3 different ports.
First suggestion - turn off dithering (e.g. addLeds<WS2812,PIN>(leds, NUM_LEDS).setDither(0)
Second, how many leds are you running? That has the potential to limit your frame rate as well.
Thanks @Daniel_Garcia , i’ve all tried with that dithering: on, off, brightness full or not… that doesn’t change anything.
I’m controlling 232 leds, it’s not so much… I don’t think it comes from the frame rate as i’m able to make the same animation faster.
One more information : The longer the white light is, the less I see the flash
In which case, we’d need to see the code to make concrete suggestions for you.
I think it would be better with anti aliasiing on more than one pixel at each end but don’t really know how to do it
Also, I bet we can get that remaining floating point math out of there; that’ll help a little, too.
Ok got the floating point math out of there, but the flashing is still present 
http://pastebin.com/NDwaQSBB
Would you be able to share the whole sketch code?
Are you by chance ‘spamming’ the LEDs? Too fast a frame rate?
I didn’t add a delay to try and keep the wave function accurate, but I don’t think that the frame rate is too fast with 232 leds. I bet this is more a conceptual challenge than a technical one…
With my Arduino Micro, I get ~210 fps with the code you posted. So if you are using a Teensy, you are getting a higher fps than I am. You should check the frame rate yourself:
LEDS.countFPS();
Serial.println(LEDS.getFPS());
