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My understanding is that pixels are an abstract unit of measurement. They have no tangible size until rendered on a display (or paper).

This leads me to believe that I should create icons on displays that are of a lower resolution (a non-Retina display) than the target display (an iPhone 5). A 120x120-pixel icon is much larger on my low-res screen than on an iPhone. This means the pixels, as rendered on a low-res monitor, are larger. And, with larger pixels, I can control positioning of items much more precisely, right?

I know that I am wrong, but please tell me why.

(I am using Pixelmator. I don't see where to adjust pixel "size". maybe that is a setting?)

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I don't think you're entirely wrong.

If you're designing on a retina display, you know that what you're seeing as you design is exactly what is going to be seen by other retina users - but you're going to need to test the images on a lower res display to know for certain what your average user is going to see. The reverse is the case if you're designing on a low res display.

However, I think that your bullet point is nonsense. Yes, you shouldn't design your images on an iPhone, but lets assume you're using retina a desktop ;)

For one, if you open up a 120x120 image on your retina display, the OS will scale it up to appear to be the same size (if you measured with a ruler) as on a half resolution display (it may differ slightly depending on scaling settings - but Mac OS X don't even give you the option of viewing the image at actual size and doubles the size as standard). So you're not suddenly working on an image a quarter of the size.

Secondly, even if you were, it wouldn't matter - you'd just zoom in. Setting "pixel size" = zooming in and out. Photoshop is even kind enough to show you the outline of each pixel if you zoom in far enough (400% or so).


Just noticed that you said "pixels are an abstract unit of measurement". Again thats right and wrong (before the advent of the retina display, I'd probably have just said wrong).

In terms of your screen, a pixel is absolutely a physical thing (and hence in no way abstract), if you have a 1024x768 monitor, there are 768 rows of 1024 physical squares, each with a red, green and blue component.

So when you save a 100x100 image, that means when you open it up its going to occupy 100x100 physical pixels on someone's screen. If you have a non-retina iPhone, the image appears smaller purely because the physical pixels of the screen are smaller (and if you really had a 1024x768 16" display, guaranteed a non-retina iPhone would have smaller pixels), if you have a retina iPhone then this is still the reason why, but iOS is also making the image bigger because 100x100 would be so tiny otherwise.

  • I guess what I'm say is that, as I can't figure-out how to scale-out in Pixelmator, I could just do it by hand and decrease the resolution of my monitor. I have found conflicting info rgd. pixel, dot pitch, pixel count, resolution, ppi, sub-pixels, etc. No idea if more ppi is better than a smaller dot pitch. I'll just keep googling. Once I understand, I'll own the concept of pixels which is where to start for learning graphic design I think. thanks. – user3634422 May 14 '14 at 19:27
  • @user, I just went off on a massive tangent in my answer ;) don't think it'll provide any extra insight. Unfortunately I don't have a clue about Pixelmator, so I suspect that's why there's a bit of miscommunication and I don't have much help to offer. Feel free to unaccept this answer in hope of receiving some more answers, I won't take it personally ;) – OGHaza May 14 '14 at 19:54
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In Pixelmator, VIEW > ACTUAL SIZE will render the file you're working on in a 1 image pixel to 1 screen pixel ratio.

While that's physically bigger than what you'll end up seeing on your iPhone retina screen, that is all the data.

What you don't want to do is put so much detail into the retina version that it gets lost on non-retina device. A quick way to test that is to go to VIEW > ZOOM OUT until you get to 50%.

(This all holds true for non-retina macbooks. If you have a retinal macbook, this may differ slightly. I'm not entirely sure how raster image editing tools handle the workspace on a retina screen.)

So, to answer the question: the resolution of your display really doesn't matter.

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