Zworykin later abandoned research on the Image Dissector, which at the time required extremely bright illumination of its subjects, and turned his attention to what became the Iconoscope. In a 1970s series of videotaped interviews, Zworykin recalled that, "Farnsworth was closer to this thing you're using now [i.e., a video camera] than anybody, because he used the cathode-ray tube for transmission. But, Farnsworth didn't have the mosaic [of discrete light elements], he didn't have storage. Therefore, [picture] definition was very low... But he was very proud, and he stuck to his method." Contrary to Zworykin's statement, Farnsworth's patent number 2,087,683 for the Image Dissector (filed April 26, 1933) features the "charge storage plate" invented by Tihanyi in 1928 and a "low velocity" method of electron scanning, also describes "discrete particles" whose "potential" is manipulated and "saturated" to varying degrees depending on their velocity. Farnsworth's patent numbers 2,140,695 and 2,233,888 are for a "charge storage dissector" and "charge storage amplifier," respectively. In 1931, David Sarnoff of RCA offered to buy Farnsworth's patents for US$100,000, with the stipulation that he become an employee of RCA, but Farnsworth refused. In June of that year, Farnsworth joined the Philco company and moved to Philadelphia along with his wife and two children. RCA later filed an interference suit against Farnsworth, claiming Zworykin's 1923 patent had priority over Farnsworth's design, despite the fact it could present no evidence that Zworykin had actually produced a functioning transmitter tube before 1931. Farnsworth had lost two interference claims to Zworykin in 1928, but this time he prevailed and the U.S. Patent Office rendered a decision in 1934 awarding priority of the invention of the image dissector to Farnsworth. RCA lost a subsequent appeal, but litigation over a variety of issues continued for several years with Sarnoff finally agreeing to pay Farnsworth royalties. Zworykin received a patent in 1928 for a color transmission version of his 1923 patent application; he also divided his original application in 1931, receiving a patent in 1935, while a second one was eventually issued in 1938 by the Court of Appeals on a non-Farnsworth-related interference case, and over the objection of the Patent Office.