A method of coding image data performed by at least one processor, may include: receiving information regarding a data block of an image; determining whether at least one of a height or a width of a residual coding block corresponding to the data block of the image is greater than or equal to a pre-defined threshold; and based on determining that the at least one of the height or the width of the residual coding block is greater than or equal to the pre-defined threshold: identifying or generating a reduced-complexity residual coding block by reducing the number of non-zero coefficients in the residual coding block; and performing transform coding of the reduced-complexity residual coding block using a line graph transform (LGT) core to perform direct matrix multiplications for each of the horizontal and vertical dimensions of the reduced-complexity coding block.