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Another new feature added by the DIGIC 5+ processors is the ability to shoot multiple exposures, where several images are ‘stacked' on top of each other. The DIGIC 5+ processors allow image stacking of between two and nine separate frames to create one signal final image. This feature is available for both RAW and JPEG images, though if M-RAW or S-RAW are set, the recording quality will automatically switch to RAW.
As befitting a digital multiple exposure there are several exposure settings that can be adjusted to tailor the final output to suit your needs. These are Additive, Average, (Comparative) Bright and (Comparative) Dark.
The Additive exposure control is for those used to shooting multiple exposures with film cameras. Instead of taking each image with the correct exposure, the total exposure is added up from each individual image. To achieve the correct result, you should underexpose each image so that the resulting image is correctly exposed once they are all combined together.
The Average setting provides an automatic exposure control whereby each image is automatically underexposed so that the final image is then correctly exposed. Unlike with the Additive setting, all images in the multiple exposure will be averaged and taken at the same exposure level setting.