In a survey of eight markets, including the UK, which together account for three-quarters of the world's advertising expenditure, the agency found that adspend in real terms would grow this year for the first time since 2000. Elections in Canada and the US would also bolster the advertising economy.
The level of growth in 2004 - 3.2 per cent - is below the 5.4 per cent enjoyed in the second half of the 90s, but is stronger than it will be over the next three years.
In the UK, outdoor, radio and the internet will be the star performers, growing by 8.9 per cent, 7.2 per cent and 16.9 per cent respectively.
In television, according to ZenithOptimedia, charter review means that the BBC is likely to concentrate on public service broadcasting, which should make it easier for commercial channels to supply more impacts.
However, with the Olympics on the BBC, there will be a nominal 4.2 per cent growth in TV advertising, subsiding to 3.9 per cent in 2006.
The newspaper industry is in for a rougher ride, with demand for print advertising remaining weak. ZenithOptimedia believes that the broadsheets' investment in tabloid versions is merely shifting patterns of consumption among existing readers but doing nothing to recruit new ones.
Therefore, the nominal growth in newspaper and magazine adspends are likely to be wiped out by inflation.