An intra-frame encoding method, an intra-frame decoding method, an encoder, and a decoder, where the intra-frame encoding method includes obtaining reference pixel values of a current picture block obtaining a predicted value of a first-type pixel in the current picture block according to the reference pixel values of the current picture block using an intra-frame prediction algorithm, obtaining residual values of the first-type pixel, obtaining transform coefficients according to the residual values of the first-type pixel, quantizing the transform coefficients, reconstructing the first-type pixel according to the quantized transform coefficients and the predicted value of the first-type pixel, and obtaining a reconstructed value of the second-type pixel according to the reconstructed value of the first-type pixel using an interpolation method. Hence, flexible encoding can be implemented, and encoding efficiency can be improved.