An image processing device 300, a non-transitory computer readable storage medium, a monitoring camera 200 and a method 100 of pre-processing images of a video stream before encoding the video stream are disclosed. The images are obtained S110, wherein the obtained images have a first resolution. The obtained images are subsampled S120 to intermediate images having a second resolution lower than the first resolution and lower than a third resolution. The intermediate images are upsampled S130 to output images having the third resolution, wherein the third resolution is the same for all images of the video stream.