NAIROBI (Reuters) - Official results from Kenya s repeat presidential election on Thursday are likely to take several days to collate, election officials told Reuters, due to changes in the process to try to make it more transparent. The Supreme Court on Sept. 1 ordered a repeat of the election after judges annulled the results of an Aug. 8 poll, pitting incumbent President Uhuru Kenyatta against opposition leader Raila Odinga, due to procedural irregularities. Official results said Kenyatta won on Aug. 8 by 1.4 million votes, but Odinga said the vote was rigged. Odinga has refused to participate in Thursday s rerun because he said election officials have not carried out sufficient reforms. Judges criticized the election board for rushing to announce the official results based only on numbers sent from the polling stations, without having the tally forms from all 40,883 polling stations showing the results. The paper forms are a back-up system meant to help prevent rigging. The board has up to a week to announce official results. This time, polling stations will only transmit scanned images of tally forms from polling stations, not numerical results, Andrew Limo, spokesman for the election commission, said on Tuesday. The scanned images will be posted online. The election board will collate and publish results by constituency once all polling stations there have reported. This could take several days in rural constituencies with poor phone networks and far-flung polling stations. There are 290 constituencies. Without Odinga running, Kenyatta is the firm favorite to win. The other six candidates failed to poll more than 1 percent in the August polls; one has since been disqualified for bankruptcy. Odinga has urged supporters to boycott the ballot and opposition leaders have called for protests on the day of the elections.  The key thing to watch in this election will be turnout,  said Murithi Mutiga, a senior regional analyst for the International Crisis Group, a global thinktank.   This will really be a referendum on the legitimacy of Kenyatta s second term.   Just over 79 percent of Kenya s 19.6 million registered voters cast a ballot in the last poll. 