A method and apparatus of image coding performed at an encoder or decoder using block prediction are disclosed. The block vector bit-count information associated with one or more block vectors (BVs) for the current block is determined, where the BVs are used to locate one or more block predictors for the current block. Prediction residuals corresponding to differences between the current block and the block predictors are determined. A first cost comprising the BV and residual bit-count information associated with encoding the prediction residuals using the first coding tool is determined. The second cost comprising the BV bit-count information and without the residual bit-count information is also determined. The derivation of the BV bit-count information and the prediction residuals for the current block are performed only once, and the BV bit-count information and the prediction residuals are used by the first coding tool and the second coding tool.