Which Pixel Aspect Ratio do I use for 300 dpi sheet fed press or 4/4 offset litho over a 1/0 PMS?

Hope I'm in the right place to ask my questions. There was no photoshop specific community, just this Ecosystem and Beta.

By @spotte10353908

You posted in the right place. The reason it says “ecosystem” is that Photoshop is no longer just one application, it now encompasses the Mac/Windows desktop version, the iPad version, and the web version of Photoshop, which can all sync documents among each other and have common features, so they are all discussed in the same place. Tech/marketing people tend to call this an “ecosystem,” even though most regular customers associate the word “ecosystem” with nature, not with tech products. So the way they use the word “ecosystem” is a little confusing to those outside the industry.

I am trying to create a 1280 x 720 pixel file. Why is that when I set up a file at 300dpi or 72dpi, I still get the same size file size? All I'm doing is changing the resolution from 300 to 72 dpi. 

By @spotte10353908

You already answered your own question. You said it’s 1280 x 720 pixels both before and after you change the ppi resolution. Well, the number of pixels is a major factor in file size, and you said the number of pixels did not change, therefore the file size should not be expected to change. The number of pixels did not change probably because you did not resample the image when resizing.

Now, I get what you’re saying: A file with a lower ppi resolution might be thought to create a smaller file size. But that is not always true. It is true only when the image is also resampled, that is, when the number of pixels actually changes. How would you get it to do that? Well, you left out a key dimension, and that is the image’s physical printed dimension in inches.

72 ppi creates a smaller file size than 300 ppi if the inch dimension is maintained. 

Example:

You have a 1280 x 720 px image, and you say it is 72 ppi.

That implies that the current intended print width is 4.266 inches, because 1280 pixels/300 ppi = 4.266 inches.

So if you want that image to stay 4.266 inches wide but at 72 ppi, then 4.266*72 = 307.152 or 307 pixels wide.

Therefore, if you want the file size to go down for an image printed that needs to be printed at 4.266 inches wide, and you are changing the ppi from 300 ppi to 72 ppi, then it will go from 1280 pixels wide to 307 pixels wide. Fewer pixels, so smaller file.

All of the above can be done in Photoshop in the Image > Image Size dialog box, if you enable the Resample option.

And if you need to print the image a width other than 4.266 inches, tell us what print width it’s supposed to be, because that will definitively set how many pixels it will be at 300 ppi or 72 ppi.

---

@spotte10353908 wrote:

Second question: Pixel Aspect Ratio?

Which one of these do I use for 300dpi 4/4 offset litho with over a 1/0 PMS metallic coat?

---

Ignore pixel aspect ratio.

Do not confuse pixel aspect ratio with frame aspect ratio.

Do not change pixel aspect ratio, for two reasons.

One, pixel aspect ratio comes from video editing, and is absolutely irrelevant for print. Printed pixels are always 1:1 aspect ratio.

Two, even if you work in video, non-square pixel aspect ratios are no longer commonly used. They were common with NTSC and other pre-HD formats, but today, all digital HD video formats use 1:1 (square) aspect ratio.

The non-square pixel aspect ratios you see in Photoshop are there only to handle frames from old video formats, and even older image formats from 30 or 40 years ago. You do not use non-square pixel aspect ratios today.

If you are not editing for old video formats, then it is the frame aspect ratio you want to pay attention to.

---

@spotte10353908 wrote:

Web legacy: Is exporting for web (legacy) the only way to reduce the file size? Somebody point me to the section of the manual that explains the new formatting. It's not illustrator. I don't want an artboard.

---

No, the primary way to resize is the Image > Image Size dialog box I mentioned earlier.

Save for Web (Legacy) is just one way to export, but many of the other export commands in Photoshop also let you resize. But because they are export commands, their purpose is to resize on the way out of the application. For normal, everyday resizing, you should be using Image > Image Size.

What is square pixels?

Pixel that has both sides equal, use that option. Other options are for previewing different screens or devices, won't change anything anyway.

Web legacy: Is exporting for web (legacy) the only way to reduce the file size?

No, use Save As to save as JPEG, for example, and to reduce file size by reducing quality settings. If you going to print its not recommended to save with low quality.

Irritating template window: Anyone know how I get rid of their irritating template window? I don't want Adobe's custom templates.

Go to Preferences > General and check Use Legacy "New Document" Interface.

"1280 x 720 at 72 dpi is smaller than 1280 x 720 pixels"= NOT IT IS NOT!!

They are exactly the same image- same pixels. Only the metadata entry for PPI is different.

Differing PPI values in metadata do not change the MB sizes of the image.

https://www.photocascadia.com/the-72-ppi-web-image-myth/

"Irritating template window:"-  Create you own template and Save it to appear in the 'Saved' tab.

Or Use the option for [Use Legacy New Document Interface] option in Preferences-