January 2015

Potential issues with JPEG compression:

This month, in honor of his recent Inpho Reseller Training in Stuttgart, Germany, we are offering an INPHO Tech Tip by Steve Hamilton.

In Inpho OrthoVista, JPG compression in the input images can cause issues with multiple single-pixel seamlines being generated.  This creates a mosaicking issue and slows down processing considerably. In general terms, background orthophoto pixel values of zero (0) are treated as unsubstantiated and are not included in seamlining/feathering operations.  When JPG compressed, the background zero values become “substantiated”, or are assigned some value other than 0, which causes them to be included in subsequent seamline generation and mosaicking operations.

If you look closely at the image, you can see that the zero-value pixels with triangular seamlines are adjacent to background pixels that have been assigned a grey value other than 0, forcing seamline generation.

When processing orthophotos for subsequent mosaicking and feathering operations, especially when using aerial imagery flown “off-axis”, or in some direction other than N-S or E-W, it is best to forego image compression to avoid inadvertent creation of background pixels with brightness values of 1 or greater.