Illustration of the size measurement process for VUDS 510799304 at z = 2.4281. From left to right: (1) the original F814W image from COSMOS (Koekemoer et al. 2007). (2) The same image after smoothing by a Gaussian kernel of 1 pixel width and extending over four times the width. This kernel ensures an improvement in signal to noise for low surface brightness levels while preventing a significant boost of noisy pixels, which would incidentally increase the measured radius if the kernel were too large. (3) The segmentation map obtained after running the detection algorithm including all pixels greater than kσ. (4) The selection of the target galaxy. All panels have 1.77′′by 1.77′′and the orange circle has a radius of 0.5′′. The total size is computed from the number of pixels in the last panel.