Illustrator: Trying to export PNG at fixed size and 128 dpi

Question

I'm designing for a screen that has the following specifications:

• 4.3” Diagonal

• Screen Size 272 x 480 dots

• Pixel Size 0.198 x 0x.198 mm

• Actual Area 95.040 x 53.856 mm

• 53.856 mm = 2.12 inches

• 95.040 mm = 3.74 inches

• 272 / 2.12 = 128 pixels / inch horizontal

• 480 / 3.74 = 128 pixels / inch vertical

I have, say, an icon in Illustrator. It is 13px x 20 px (the Artboard is 272 x 480). When I export it at 72 dpi, it comes in at the right size, but this is half the pixel density that the screen is capable of. When I try to export it at 128 dpi, it becomes larger.

Note: I do not have 'use artboards' checked, because I want to just export this one icon.

This doesn't quite make sense to me, Is there a way that I can constrain the size in physical units (mm, in) and still have the resolution that I need?

Thank you for your help!

Answer 1

Most systems ignore PPI settings, it is basically only useful for print*. But its so ingrained in adobes workflow that they cant drop it. Basically 72 PPI is the closest thing to "no resolution" as adobe can manage.

Now in fact it makes very little sense to have a unit size for pixels. Because pixels can have arbitrary sizes, and different parts of your artwork may in fact have different densities. But its been added there for the simple purpose that some users want to think in pixels. There is basically 2 ways of doing this:

• Make fixed size, so they use the NOT set size.
• Make a flexible size, but ultimately this is VERY confusing for your average Adobe user (who really does not even understand what PPI is).

So either design in pixels or units. Then don't use save for web but just save it allows you to plug in a value directly.

Note the PPI value does not matter. There is no such thing as pixel density on the digital image not intended for print. All teh digital system cares about is pixels. The PPI value has no significance for the image output!

* So only useful for outputs that are not digital. So does not matter one pixel is one pixel, PPI has on effect that or even the quality of the pixel.

In fact PNG does not even have a PPI field, it is just in the Adobe extension. PNG does have a physical resolution field that can't be set to exactly 72 PPI, which not many programs support it. And adobe will ignore it and use its own extension... Be very careful with PPI and PNG because of this.