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I'm learning this right now and have some problems getting it the right way. I now know the resolution should be 360 inside a photoshop to fit for all kind of scenarios for printing the image, however I have doubts of how to do this right and got several questions:

1) When stock photos are downloaded from the web, they are with big dimensions, but with low resolutions. I tried pixabay, because they are free, and found the images are at 72 res. Is this the same with paid stock photo services too? If so, what are the alternatives?

2) When I open up the downloaded stock image with a size of 2.5m in photoshop, and then open the Image Size window(ctrl+alt+i), I see the Image Size property of around 50(!)m. How and why is this so?

Thanks!

  • 'I now know the resolution should be 360 inside a photoshop to fit for all kind of scenarios for printing the image,' 360 what? There is no 'one-size fits all' when it comes to print. This information is incorrect. You should design for the specific print medium you need to print. – Summer Jan 6 '17 at 11:01
  • Thanks, but could you reveal a little bit more about this, please? And what do you mean by "print medium"? P.S. I meant 360 PPI – styleinside Jan 6 '17 at 11:15
  • I think Chris just gave a great answer, but by print medium I meant what you want to print and with what kind of printer. ie business cards, newspaper, flyers, flex print on a t-shirt etc. The best way to go is to pick a printer, choose what you need to print (so if you're asked to do business cards, pick that) pick a size etc and look at the delivery specs. – Summer Jan 6 '17 at 11:51
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As has already been pointed out in the comment above, your assumption about a resolution of 360 is incorrect. The necessary resolution is dependent on the final use of the image. A good rule of thumb is that the image resolution should be twice the screen frequency of the printing method. So a magazine printed at 175 line screen would require 350dpi images for optimum quality, while a carton printed at 85 line screen would only need the images to be 170dpi. Different rules apply to digital printing, but in either scenario the print company should be able to provide you with a specification for what is required.

Supplying files at 72dpi, but with large dimensions is common practise, but this varies from supplier to supplier and many of the more professional image sources provide images at 300dpi by default or at least offer that as an option. It doesn't matter which way the file is supplied because you can go to Image Size in Photoshop and adjust the size. Be sure to uncheck the Resample Image option so that the resolution increases as you reduce the dimensions. Scale the image to the size that you need, check that the resolution is high enough (see above) and if the resolution is way too high then so back to Image Size and reduce the resolution (this time with Resample Image checked).

The different file sizes that you are seeing are the compressed and uncompressed sizes. The value in Photoshop is the uncompressed size of the actual image data which is fixed for a given size, dpi and colour mode. The smaller number is the size of the file after compression and this will vary for different images and file formats. For example, the data for an A4 CMYK image at 300dpi will be roughly 32MB, but the file size will generally be MUCH less, depending on the compression method and amount of compression applied.

There are many resources for information on this topic on GDSE, just search for things like 'image size' and 'resolution' and keep reading and experimenting until it makes sense.

  • Wow, thanks a lot, Chris, for detailed explanation of this! This is very helpful! – styleinside Jan 6 '17 at 12:13

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