Recent missions such as Planet Labs Dove have shown relatively high resolution imaging capabilities using CubeSats, with resolutions up to 5 m. Such resolutions are sufficient in capturing large characteristic features of agriculture, deforestation, or disaster. However, multi-band imaging is required in acquiring normalized difference indices, which help identify such characteristic features. Due to the limitations of mass and volume in CubeSat, a multi-bandpass filter must be applied and the image data must be decomposed. This paper discusses a simple decomposition method for an onboard imager.