In order to run a good quality comparison, GlobalVision turns a PDF’s vector elements into a fixed grid of pixels through a process called rasterization. This allows the software to graphically compare and inspect the image pixel by pixel.
Since file types such as PDFs are not saved as individual pixels but instead as mathematical formulas known as vectors; they can be flexible in their scale, and viewable at different rasterized resolutions, making them ideal Reference or Master documents for your comparisons.
The number of pixels rasterized within an inch of space is known as your Pixels Per Inch, or PPI.
Since we inspect printed material, where each pixel may be printed as an individual dot, we can also use the equivalent term Dots Per Inch, or DPI.
This concept is important to your inspection, because in order to run a successful comparison you need the rasterized resolution of both your files to be the same.
Normally, this is done automatically, where digital PDF documents are rasterized at 300 DPI right when you import them.
For the grand majority of use cases, a DPI of 300 will be sufficient and should be the default selection.
However, if the need arises for you to change the system resolution, this is where the "system resolution" feature comes in.
Under Menu > System Resolution you can choose between the available options (DPI: 300,400,600,800,1200, or Custom).
Does the system resolution affect my scan resolution?
No, unlike PDFs, scanned images are not saved as scalable mathematical vectors, but are instead saved as JPG, PNG or TIFF files, where individual pixels are stored onto a grid.
Given that a scan is an image of a real world, printed sample, it can not be rasterized at a different DPI. That is why if you try to make this type of image larger, it starts to look "pixelated".
In fact, one of the most common issues causing a failed inspection is when the DPI of both your master and sample documents do not match.
If you scan a physical sample at 200 DPI, then it will be imported into the system at 200 DPI. The only way to change the DPI of a scanned image is to re-scan at the correct DPI. You can do this by adjusting your scanner software settings.
For the majority of use cases, a scanned DPI of 300 is optimal.
If I increase my DPI, will I get a better inspection because i have a more detailed, higher quality image?
Not necessarily, it depends on a variety of factors including the substrates you’re printing on, the size of the printed sample, and the variety within your material. Sometimes, increasing the DPI can add unnecessary noise to your inspections and result in more false positives.
There are certain situations, however, where a larger resolution would be beneficial. For example, a very small label with a tiny QR code might require scanning at 600 DPI for proper inspection. Just remember to set the corresponding system resolution to 600 DPI too, in order for both your master and sample documents do match.
Is there a case where I should reduce my system resolution?
If the size of your digital file is too large (above 32K pixels in either width or height, or larger then 1GB), you might notice some performance issues. In this case, reducing the system resolution using the custom option might improve the performance of your files.
