Image Sizes (DPI)

[Danger Phoenix]

I'm working on customer communications for a client, where we are designing emails, PDFs and prints (via a large scale supplier).

The print supplier has said they want all images in 600dpi to maintain the quality when they print, but this would then inflate the sizes of any PDFs we store.

I believe the generally used DPI for email is 96, but doesn't 600dpi seem overkill for print?

 

[gord]

I'd have thought email would be 72 like most other web images.

I'd only require 600 for an exceptional portfolio shot or print where I know the viewer might get up close and personal. Everything else would be 300.

Do you know what sort of sizes/purposes they plan to print at/for?

 

[Danger Phoenix]

We are talking about printing logos and small adverts on A4 paper... nothing major really.

 

[simisker]

My email design company now supply all images for our emails at 150ppi, as a large portion of people now read their emails on retina/other high-density devices.

Also, responsive email layouts tend to expand images to fit the full width of mobile screens, so it's a good idea to ensure that the information is there when images are 'enlarged' in this manner.

edit: 600 does seem overkill in my experience of print; I've never had a problem with 300ppi files sent for publication.

 

[gord]

We are talking about printing logos and small adverts on A4 paper... nothing major really.

Sounds like they might be covering themselves in-case they need to go to A3 or A2.

My email design company now supply all images for our emails at 150ppi, as a large portion of people now read their emails on retina/other high-density devices.

When you say 150ppi do you mean they supply images at twice their original pixel size?

 

[simisker]

Sounds like they might be covering themselves in-case they need to go to A3 or A2.

Good point!

When you say 150ppi do you mean they supply images at twice their original pixel size?

Aye [so 144ppi if you want me to be exact]. We use double-sized PSDs when mocking up, determining layout or creating assets. Obviously you have to keep an eye on file weight, but for photos you can lower the compression quality of JPGs to compensate, without any visible loss of image quality.

 

[gord]

Right, yeh 150 just seemed odd because it wasn't exactly double and dpi/ppi has no effect on screen image dimensions.

 

[Danger Phoenix]

We will never go to A3 or A2 as these are customer letters... if anything we would go smaller to A5.

What is the difference between PPI and DPI?

 

[gord]

What is the difference between PPI and DPI?

There's a lot of articles online that try to clear it up because DPI was commonly used where many meant PPI.

But basically your printer has a DPI and your image has a PPI. The printer can print X number of dots in an inch. An image will have X number of pixels in an inch. If you make the image bigger you stretch the pixels out meaning a lower PPI and lower quality image.

 

[asim18]

I believe the generally used DPI for email is 96, but doesn't 600dpi seem overkill for print?

Absolutely not. And perhaps not.

~96 dots/pixels per inch is the pixel density you see on typical computer monitors.

When you print an email it is not sent at 96dpi to the printer. A 96dpi text print would look absolutely horrendous. Imagine a 10x10 grid packed into one square inch. No resolution at all let alone any resolving power for anything below 18pt text.

Text isn't stored as dots/pixels, and 600dpi is very high, but not overkill for images. A 10 megapixel photograph at 6x4 inches will have about 645ppi of resolution.

 

[Danger Phoenix]

We want to keep the size of PDF outputs to a minimum, so we are concerned that having a few 600dpi images in there will inflate the size.

The emails we send could be viewed on any device or even printed, so what DPI and PPI would we use for this?

I did some reading on DPI and PPI but still find it quite confusing

 

[Sasahara]

Do both?

600 DPI is good if you have small bitmapped text or similar fine bitmap images for commercial printing.

Personally I'd keep the compression levels high or off for PDFs that are intended for printing (where you want reasonable quality).

96 PDI with high quality compression or none will print reasonably well on a desktop inkjet/laser printer as they have hardware that smooth's out the pixels.

 

[asim18]

We want to keep the size of PDF outputs to a minimum, so we are concerned that having a few 600dpi images in there will inflate the size.

The emails we send could be viewed on any device or even printed, so what DPI and PPI would we use for this?

I did some reading on DPI and PPI but still find it quite confusing

I understand you want to keep PDF size to a minimum, however your printers want to keep quality to a maximum.

Ideal thing (and most publishers do this) is to create separate print and web PDFs. Just set the PDF you send to the printers to whatever they require then just down-sample your PDFs for electronic distribution.

PPI is only used when representing a digital pixel based image as a spacial/physical object. It has no relevance when viewed on screen because a pixel in a digital image represents a pixel in a digital flat panel. When you have a pixel from a digital image represented in a physical/spacial object you need to tell something how much actual physical space one digital pixel must take up.

 

[john_s]

Imagine a 10x10 grid packed into one square inch. No resolution at all let alone any resolving power for anything below 18pt text.

Is DPI/PPI not dots/pixels per *linear* inch, as opposed to per *square* inch, so ~100dpi is a grid of 100 x 100 dots, not 10 x 10 as you suggest?

 

[gord]

Is DPI/PPI not dots/pixels per *linear* inch, as opposed to per *square* inch, so ~100dpi is a grid of 100 x 100 dots, not 10 x 10 as you suggest?

That is correct.

This is a good article on the subject: http://99designs.com/designer-blog/2013/02/26/ppi-vs-dpi-whats-the-difference/