TWO STEP IMAGE DOWNSAMPLING METHOD AND APPARATUS

摘要

The invention describes a method for converting a first image having a first high resolution into a second image having a second lower resolution. The first image ( PHR) is a compressed image comprising a number of blocks (BB) each having a first amount of transformation coefficients (cij ). The second image (PLR) is a decoded image comprising a second amount of pixel values (vfkm), the second amount of pixel values being smaller than the total amount of the transformation coefficients (cij ) of all blocks (BB) of the first image (PHR) - The method comprises the steps of downsampling by a target downscaling factor (starget) for reducing the resolution and decoding the transformation coefficients (cij ) to the pixel values (vfkm). The step of downsampling is carried out stepwise with a first and a second downsampling step, wherein a first downscaling factor (S1) is used in the first downsampling step and a second downscaling factor (S2) is used in the second downsampling step such that the target downscaling factor (starget) equal s the product of the first and second downscaling factors (s1, S2) -