Nomura Securities’ Michael Nathanson fires the warning shot this morning as he lowered his Q2 earnings per share estimates for Viacom, News Corp, Time Warner, and Scripps Networks — but raised for Disney and Cinemark. (He left CBS, Discovery, and Regal unchanged.) Nathanson says that investors may be surprised after showering so much love on media companies in the first half of 2012. For example, Scripps shares were up nearly 30% followed by Disney (+28%), Discovery (+26%), News Corp (+23%) and CBS (+19%). But most of the increases were due to the market’s optimism about media — not from solid improvements in earnings. Perceptions could change later this month when companies begin to file their Q2 numbers. With television’s scatter ad market weakening, “We expect national broadcast and cable network advertising to decelerate” from 6.5% year-over-year growth in Q1 to just 2.2% in Q2, he says. And although Nathanson wasn’t disappointed by the recent decline in movie ticket sales — as several other analysts were — he says that the results were lopsided. “Disney, Lionsgate and Sony led the way, but this was offset by difficult comparisons at News Corp, Universal and Time Warner.” The bottom line: Nathanson reduced his Q2 earnings per share forecast for Scripps by 13% to 87 cents with Time Warner -5% to 57 cents, News Corp -3% to 31 cents, and Viacom -2% to $1. He raised Disney 3% to 93 cents and Cinemark 8% to 37 cents.