ACR; TAKING OFF; MADE LOW ALT TURN TO AVOID POSSIBLE CLOSE PROX WITH GA-HELICOPTER.

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RWY 28 WAS THE ACTIVE. I WAS WORKING LCL CTL. VFR WX CONDITIONS; BUT VIS HAZY (4F). GA HELI X WAS WORKING LOW LEVEL OVER THE CITY (5 MI S OF THE ARPT) TAKING PHOTOS; TALKING TO ME. HELI X RPTED 3 MI S OF THE ARPT INBND FOR LNDG. HE IS A LOCALLY BASED ACFT WHO HAS A LNDG AREA AT THE SW CORNER OF THE S TXWY (HOTEL) WHICH RUNS PARALLEL TO RWY 10/28. I TOLD HIM TO PROCEED INBND AND REMAIN S OF RWY 10/28. ACR Y CALLED READY FOR TKOF. I TAXIED HIM INTO POS AND HOLD TO WAIT FOR AN SMT THAT HAD JUST DEPARTED TO TURN OUT OF THE DEP LANE. I THEN CLRED ACR Y FOR TKOF. HELI X IS NOT IN SIGHT; YET I AM USING RADAR SEP VIA THE BRITE. AT THE POINT THAT X WAS IN SIGHT AND Y HAD ALREADY STARTED HIS TKOF ROLL (X IS NOW OVER H PARALLEL TO RWY 28). I DID NOT FEEL IT WAS NECESSARY OR ADVANTAGEOUS TO MAKE A XMISSION TO ACR Y AT THIS POINT; TO ADVISE HIM OF THE HELI. BOTH ACFT WERE IN SIGHT AND I WAS APPLYING VISUAL SEP AS PER 7110.65 7-10 PAR A1+2. THE NEXT XMISSION WAS UNINTELLIGIBLE. LATER; LISTENING TO THE TAPE; I LEARNED THAT ACR Y WAS MAKING A RIGHT TURN BECAUSE OF THE HELI. NOTE: THAT SECTION OF THE TAPE HAD TO BE LISTENED TO 3 TIMES TO DETERMINE COMPLETELY WHAT HIS XMISSION WAS. SINCE I MISSED THE XMISSION I NEXT CLRED X TO LAND. ACR Y THEN SAID HE WAS GOING TO RPT A NEAR MISS WITH THE HELI. PLT OF THE HELI ADVISED THE SUPVR HE WAS OVER H. THE DISTANCE BTWN THE CENTERLINE OF H AND CENTERLINE OF RWY 28 IS 700'. PLT OF ACR Y ADVISED THE SUPVR THAT HE FIRST SAW THE HELI WHEN HE WAS ROLLING AND ADJUSTED HIS ACFT ACCORDINGLY TO ALLOW FOR THE RIGHT TURN TO AVOID THE HELI. THIS IS AN EVERYDAY OPERATION FOR THIS TWR AND THERE ARE NO LCL PROCS MANDATING AN EXCHANGE OF TFC. VISUAL SEP WAS APPLIED AS PER THE 7110.65. I HAD RADIO CONTACT WITH BOTH ACFT. I HAD BOTH ACFT IN SIGHT. EXCHANGE OF TFC WAS NOT NECESSARY; TFC WAS NO FACTOR IN MY OPINION. IT HAS BEEN MY EXPERIENCE THAT XMISSIONS SHOULDN'T BE MADE TO ACFT IN A TKOF ROLL STATUS UNLESS ABSOLUTELY NECESSARY.