That’s a very important point. To violate the law you must have entered the intersection when the light was red. That means if any smidgeon of your bumper is over that first white line of the crosswalk when the light is still yellow, you are not guilty. A video is recorded of the incident, which can be very helpful in determining if your car snuck into the intersection prior to the light changing to red. That video (and the pictures) can be accessed here:
City codes: Santa Ana – SNA; Garden Grove – GGR; Los Alamitos – LOSALM
It must be proven beyond a reasonable doubt that the light was red before you crossed that first line of the crosswalk. If it is extremely close, or perhaps another vehicle is blocking the view, and there is a reasonable doubt that you committed the infraction, your case will be dismissed.