Techniques and tools for interpolation of image/video content are described. For example, a tool such as a display processing module in a computing device receives pixel values of a low-resolution picture and determines an interpolated pixel value between a set of the pixel values from the low-resolution picture. The tool uses auto-regressive edge-directed interpolation that incorporates a backward projection constraint (AR-EDIBC). As part of the AR-EDIBC, the tool can compute auto-regressive (AR) coefficients then apply the AR coefficients to the set of pixel values to determine the interpolated pixel value. For the backward projection constraint, the tool accounts for effects of projecting interpolated pixel values back to the pixel values of the low-resolution picture. The tool stores the interpolated pixel values and pixel values from the low-resolution picture as part of a high-resolution picture. The tool can adaptively use AR-EDIBC depending on content and other factors.