Precise control of both orientation and form birefringences is carried out using a single material. Hot-stretched cellulose triacetate (CTA) films containing diisodecyl adipate (DIDA) show negative orientation birefringence with ordinary wavelength dispersion, as similar to that of the pure CTA film; the absolute value of the birefringence increases with wavelength. However, after extracting DIDA from the stretched films by immersion into an organic solvent, the birefringence of the film dramatically changes from negative to positive with extraordinary wavelength dispersion; the magnitude of the birefringence increases with the wavelength. This is an inevitable property for a multi-band quarter-wave plate which is used for optical devices. Numerous ellipsoidal pores are detected by SEM observation in the film after extraction, indicating that DIDA is segregated and formed ellipsoidal domains in the CTA matrix during annealing and stretching. These results indicate the great contribution of form birefringence originated from anisotropic pores, and the combinations of orientation birefringence from CTA molecules and form birefringence from pores give extraordinary wavelength dispersion. Furthermore, the amount of an additive, annealing time and stretching condition affect the number, size, and aspect ratio of pores. Total birefringence values of CTA films after extraction increase with increasing the DIDA amount and the strain rate at the stretching process. Transmittance of CTA/DIDA decreases with the annealing time, suggesting that DIDA is segregated from CTA and forms domains during heating. Therefore, the annealing time should be minimized to keep high transparency.