To fully appreciate a custom print, we should look first at its opposite – a standard or on-line print. These prints are made in unattended, automated, serial operations. You upload your image to a server from your computer or drop it off to a photo service bureau on USB where the sales clerk adds it to the queue on the server with all of the other on-line orders. The server is connected to a series of large format printers each of which is loaded with one of the standard papers – usually gloss, lustre and matte. The idea is to herd everyone to those few common, inexpensive, resin coated papers to reap the benefits of volume processing and presumably to offer volume pricing. If better paper is also offered, there will often be just one or perhaps two smooth matte papers offered under the general moniker “Fine Art” or “Giclee.“
Once your images are added to the queue, they are pumped through to the series of printers where they are grouped together with hundreds of other images. There they are averaged and printed, as is, on large rolls of the aforementioned resin coated and matte papers. The file settings which are required for this type of print are the least acceptable for print – flattened 8 bit Jpeg, PNG, etc. in sRGB or sometimes AdobeRGB colour space, usually at or below 25mb in size. If you request a 20” x 30” print to be made from your Jpeg image which only has enough print resolution for a 5” x 7” print, the image may simply be enlarged on the fly without concern for the resulting quality loss. That’s your problem.