Sentence examples for by virtual colours from inspiring English sources
Note. that by "virtual colours" we mean the colours that are not present in and. .
Because the colour table is modified by inserting virtual colours, the reclustering is necessary to ensure that the same cluster configurations are used in the embedding and extraction phase.
In Step 3, each cluster is expanded by adding a number of virtual colours, which are not present in the original image and near the centroid of the cluster, in order to form an expanded cluster with colour.
Original imageModified image with virtual colours addedStego-image.
Therefore, the number of the virtual colours should be restricted in the expansion process.
Throughout the rest of the paper, we will use the terms physical colours to represent the colours present in the original image and virtual colours to represent the added colours that are absent in the original image.
Instead, all the physical colours are preserved while some virtual colours are added to expand the clusters in order to increase embedding capacity without inflicting high distortion.
At first glance, distortion should increase proportionally as the embedding capacity gets higher through the addition of the virtual colours.
Original imageModified image with virtual colours addedStego-image Figure 8 PECPEC-based data hiding experiments on image "Mandrill".
As discussed above, adding the virtual colours to expand the cluster size can boost the performance of PEC.
To ensure the appearance of every virtual colour in the stego-image and subsequently allow the recipient to reconstruct the same colour table, some pixels have to be chosen to have their original (physical) colours replaced with the virtual colours before data hiding takes place (step (4) of Figure 1).
