A method is disclosed for noise reduction of CT image data and an image processing system is disclosed. An object under examination is scanned and at least two CT image datasets are created, each being undertaken on the basis of a different x-ray generation process. Subsequently, the image datasets are split up into at least two split-up image datasets, with a lowest local frequency band and at least one high local frequency band. In at least one embodiment, this is followed by the determination of the noise in at least one of the image datasets for each x-ray spectrum and calculation of at least one new image dataset using an unchanged split-up image dataset in each case with the lowest frequency band and an image dataset created from a noise-minimized weighted combination of split-up image datasets, which originate from the scans with different x-ray energy spectrums.
