A Somerville man was arraigned in Middlesex Superior Court in Woburn last week on charges that he filmed women dressing in a Somerville YMCA locker room, authorities said. Ryan A. Perez, 24, pleaded not guilty to four counts of photographing an unsuspecting nude person, three counts of possession of child pornography, and wiretapping, according to the office of Middlesex District Attorney Gerard T. Leone Jr. A female Y patron reported seeing Perez “slide a cellphone out from under the door and point it in her direction’’ at about 9:30 a.m. Nov. 1, Leone’s office said in a statement. The woman alerted authorities, and Perez was apprehended in the building. Officers searched his phone and allegedly found six videos created that day, in addition to 23 images that police described as child pornography. Perez is due in court April 12 for a pretrial conference. - Matt Byrne