Can anyone tell me how to save my reworked raw file as a jpg file for printing at 300dpi? When cropping, I selected the 5:7 ratio and saved my image as a 5x7 jpg. However I could not figure out how to save it at 300dpi which is needed for printing at professional print services.
thank you for any assistance,
Mary
5 x 300 = 1500 and 7 x 300 is 2100, so your image should be 1500x2100 pixels.
In RT, 5x7 is the aspect ratio, which does not correspond to an actual pixel size, but rather the ratio of width to height for your image.
@Mary_Sullivan Iām going to assume that since you cropped using a ratio of 5:7, you want prints with a physical size of 5" x 7" at 300 pixels per inch (incorrectly referred to as DPI).
If so, resize the image to: 7*300 x 5*300 = 2100px x 1500px.
Read:
I know that 300 dpi is a āstandardā density that everybody refers to, but itās also complete rubbish. Printers (like in magazine, book or calendar printing) do not think in dpi, they use lines per mm or lines per inch, and there is no ārealā conversion to dpi.
Having said that much, everything north of 160 dpi is wasted information. The equivalent of 160 dpi is what is needed to print the GEO Calendar, and thatās as far up as quality goes in my book, so donāt let them fool you. Next thing is the distance between your eyes and the image: a postcard or legal-sized photo needs a high density, but nobody sticks his nose close to a 24" by 36" (+/- 60 * 90 cm) print. The distance between the eye and the image will - in general - never be smaller than the diagonal size of the image.
How to apply this in the real world:
number of pixels on long side required for a good print = length of paper on long side * 160 (anything inbetween 150 and 180 will do)
possible image size for good print = number of pixels on long side / 160
My personal calendar (always standard X-mas gift to the family) is printed in 12 * 18" size (30 * 45cm) and I reduce the images to 2560 dpi on the long side. As you can imagine, the print-shop was telling me that this is not good enough and 18" need AL LEAST 4800 pixels on the long side, but I told him that he shall just print what I pay for and avoid all unnecessary conversation. After seeing the result (in 2006?) he never discussed this again and we have a happy business relation for 13 years (and +/- 300 calendars printed) now.
You take my money, you do my work. 160 dpi is perfect for hi-class prints.
@beachbum you mean PPI when you write DPI. A pixel is a square, you cannot print a square square using one dot, so DPI is generally much higher than the PPI, in the ballpark of 10-30 ink dots per pixel. It would be difficult to find a home inkjet printer in 2018 which prints at a resolution of not more than 300DPI. Most home inkjet printers (I just checked in MediaMarkt) have a dot pitch of 10Āµm or less ( = 2540DPI or more).
Thatās of course not in disagreement with the argument that ~160PPI could be enough when taking into account the typical viewing distance.
@Morgan_Hardwood Yes, that may be true, but as far as this thread is concerned: the print-shop requested 300 dpi and I tend to believe this. Our print-shop here doesnāt care about dpi/ppi neither. They happily request the picture at a āresolution of 300 dpiā.
@beachbum same experience here. The print shops I used also required 300 āDPIā, they claimed they could not resize the images on their end and I should do it, and they didnāt understand what DPI was. They had no clue what an ICC profile is, even though they had professional commercial printers worth tens of thousands of euro. Such is lifeā¦
(sorry, couldnāt resist)
Yeah yesterday was a long day 
that math was at the end of it 
I totally sympathizeā¦been there!
The print service has a printer. Its ideal input could be 300 ppi (pixels per inch), although many people write dpi when they are actually talking about ppi. If the pixel dimensions of your file are less, the print service will upsize the image or let the firmware in its printer do that. If more, downsize. If you know their printer and have studied the technique, you can resize ā but generally it is fine to let the print service do it. Just save the file to a JPG without resizing.
Does the 5 x 7 print borderless? If so, you crop your image to a 5:7 ratio. If the print service needs to leave a white border, you should know that and adjust the aspect ratio accordingly.
Funny, someone just wrote a guide regarding DPI vs PPI: DPI vs PPI - What is the Difference? - Photography Life
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One caveat: That does not apply to line graphics and text, there you want all the 300 PPI you can get. Of course, those are normally provided as vector files so the printer/rip can just raster it the way it likes.