200 400 600 800 1000 1200 1400 1600 0 20 40 60 80 100 120 Averaged Dimension of Computer Graphics Figure 3: The histogram of the average dimension of the PRCG  set 2.  Natural secne content scope: Similar to the PIM image sets, the content of the images is limited to natural scene only. By setting this scope, many of the abstract or fantastic scene PRCG are excluded. 3.  Image size: The size of the PRCG varies between 400 pixels and 1400 pixels in average dimension, (width height)/2, with the mean at 645 pixels. Figure 3 shows the histogram of the average dimension of the PRCG set. 4.  High photorealism: The images are visually inspected by the au- thors to ensure their high photorealism. Incidentally, from the avail- able rendering information of the PRCG set, we can see that the PRCG images often have high quality rendering effect such as global illumi- nation, caustics effects, or camera effect like depth of field (DoF). 5.  Record of the rendering information: The associated rendering information for the PRCG is recorded during the collection process whenever it is available. See Section 4.1 for more details. 6.  Category: The PRCG are categorized according to its content type. More details in Section 4.2. 7.  Post-processing: The white border or text at the corners are cropped out and the PRCG duplicates are removed. 9