An image real-value encryption algorithm based on Logistic chaos is proposed. The transmission of encrypted information is greatly simplified while ensuring the information security. The algorithm uses Logistic chaos control to generate phase template. Based on the nonlinearity and sensitivity to initial values of the chaotic system, the key space is increased while the key volume is reduced, and system complexity is increased. In the premise of original information being restored, the obtained real-value encryption matrix is saved as low-distortion gray-scale image, which facilitates the transmission of encrypted information conveniently among users. The algorithm is simulated with MATLAB, and results show that the proposed algorithm has good robustness against noise and shear. The keys are characterized by high sensitivity, which provides strong resistance for exhaustive attack.