Perceptual Encryption is required in many of the multimedia content preview application. There is always a need of an efficient technique that reduces the overhead of encryption in real-time. In this paper we take advantage of the energy present in DCT block and have studied the effects of encrypting the selected DCT coefficient. Also the DC coefficient is further divided into bitplanes and an investigation is carried out to study the resulting depth of perceptual encryption. To measure the level of perceptual degradation, objective image quality assessment metrics such as SSIM, MS-SSIM, VIF, VIFP, VSNR, IFC and UQI are used. The presented results can help one chose the desired level of perceptual encryption according to the application with very little overhead.