When a picture displayed on a client device is enlarged, the client device may be configured to insert new pixels between two adjacent pixels in the picture. When actual values of the new pixels are stored on a server, the client device may submit a request to the server for actual values of the new pixels. Responsive to the request, the server may first calculate interpolation values in accordance with the same interpolation algorithm and then calculate a difference value based on the interpolation values and the actual values stored on the server. If the calculated difference value is greater than a threshold value, the server may transmit the actual values for the new pixels to the client device. Otherwise, the server may instruct the client device to calculate the interpolation values.