1. A method for noise reduction of computer tomography (CT) image data comprising: scanning an examination object; generating at least two CT images, each CT image being generated on the basis of a different x-ray energy spectrum, as an input image; breaking down each input image into at least two broken down image data records, each broken down image data record being associated with different spatial frequency bands; determining local band-dependent correlations between the broken-down image data records having the same but not a relatively lowest spatial frequency band; calculating at least one newly broken-down image data record by using the local band-dependent correlations of the at least two broken down image data records, with: a weighted average value of a pixel being formed from at least two pixel values of the at least two broken-down image data records if a local band-dependent correlation of a pixel is weaker than a threshold, and a pixel value of the corresponding one of the at least two broken-down image data records if a local band-dependent correlation of a pixel is stronger than the threshold; and calculating at least one new final image data record for at least one x-ray energy spectrum from the broken-down image data record with the relatively lowest spatial frequency band and the at least one newly broken-down image data record of the same X-ray energy spectrum.