I have just submitted my first design to a print shop; an advert for a magazine measuring 3.333" x 4.583" at 300 dpi. This was a simple design created in Photoshop, layering a logo over an image. When I created the file in Photoshop I set the dimensions and resolution as mentioned above and set the color to CMYK. I should mention, I created the file in InDesign as well which produced the exact same results below.
I saved the finished file as a JPEG. I noticed when I opened the file on my computer the image appeared extremely large (visually, not the file size) 1000 x 1375 to be exact. Realizing that these dimensions were 3.333 x 4.583 multiplied by 300 (The value I had set for pixels per inch), I sent the file off to the printers. I received a message back "the artwork is almost the size of a full page, please resize and resend". I had the same issue with the TIFF format.
I then saved the file as a PDF, when I opened the file on my computer, visually it looked perfect on screen (i.e it appeared actual size, 3.333" x 4.583" - not blown up, like the JPEG and TIFF formats). I sent this file to the printers and the design was approved for print.
I was initially confused about the "resolution" shown below, being only 240 x 330, I was worried it would be rejected by the printers for being way too small! I now realize this resolution is only relative to my screen and has nothing to do with the print dimensions.
Having no experience with designing for print, what I'm confused about is why the JPEG/TIFF files were rejected by the printers? Why do the JPEG/TIFFs look drastically larger on screen compared to the PDF which seems to be viewed at actual size.
The problem was resolved by saving to PDF but what I'm looking to avoid is not being able to save as JPEG and TIFF in the future if those formats are required by a specific print shop who won't accept PDFs.
Any help would be greatly appreciated.