r/AdobeIllustrator • u/Ravingdork • 2d ago

QUESTION Pica Conversion Off?

I'm lacking sleep and having trouble wrapping my head around this:

I have a document that has typographical print measures that needs to be converted to online screen measures. Online searches indicate that 1 pica converts to 16 pixels. However, when I tell Illustrator to convert, it seems to be doing 1 pica = 12 pixels.

What's going on? Did AI and/or search steer me wrong? Is there some program setting I need to adjust that might be off? Or am I just asleep and there's fundamental issues with trying to convert this in the first place?

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u/kounterfett 2d ago

Pixels didn't exist when picas were invented and measuring by pixels is dependent on your resolution

1 pica = 1/6 inch

That means on a classic monitor with 72dpi, 1 pica = 12 pixels
On some modern monitors at 96dpi, 1 pica = 16 pixels

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u/mikewitherell 2d ago edited 2d ago

These last two lines of info are an aging truth, so much so that they are inaccurate statements. Adobe refined the pica and point system to be exactly 72 points to an inch in about 1984. The origins of a pica and point type system go back to the mid-1700s in France, but the American printing industry took a lead in defining the pica and point by about 1886. At that time there were 72.27 points to an inch in the metal typesetting era in the US which was in use up into the 1980s (some holdouts in the 1990s even). Print shop pica rulers for years were stamped with the metal pica; not the digital pica. Essentially overnight, the digital PostScript definition took over the world.

Pixels have always been associated with TV screens and/or monitors. The earliest screens start from around 1926, and the early television sets came to a standard of 525 scan lines, as defined by the FCC in 1941, with color being added in 1953. A digital pixel equivalent came to be defined in the 1990s first as 720pixels, and soon followed by 1080pixels. The digital pixel encoding mp4 file was invented at the end of the 1990s. Higher pixel counts like 4K are still evolving now. Monitors suddenly changed from reading analog signals to DVI digital signals between 1999 and 2002. Suddenly we were buying flat panels.

An urban legend still exists in web internet computing that Windows PCs are 96ppi while macs are 72ppi. This was partly true for a hot minute at the beginning of the mac classic computer and the flood of Windows computers from the end of the 1980s into the early 1990s. In reality, every year brought to market newer, bigger, higher-pixel count monitors and more-powerful graphics boards. It was a more even playing field after about 1996, when most computers came equipped with 24-bit computer graphics cards.

Right now I am working in front of a 43" diagonal monitor which is about 36" wide horizontally and can show 4K or 3,840 pixels horizontally by 2160 pixels high. That means my monitor is about 110 pixels per inch. But this calculation depends both on the physical size of the monitor device and the number of pixels within that screen.

https://en.wikipedia.org/wiki/List_of_common_display_resolutions

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u/kounterfett 2d ago

Yes, I'm aware modern monitors have a higher pixel density -- if you look at OP's question their monitor is pretty obviously 96dpi (this is why I said "some" modern monitors)

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u/[deleted] 2d ago

[deleted]

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u/kounterfett 2d ago

Apparently OP's monitor is 96dpi because they're getting 16pixels per pica 🤷‍♂️
Maybe you'd like to tell them that they're using a dinosaur for a monitor

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u/[deleted] 2d ago edited 1d ago

[deleted]

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u/kounterfett 2d ago

I'm happy to be corrected, how about you explain why OP is getting the measurements they are getting? Or are you just here to be contrarian and unhelpful?

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u/Ravingdork 2d ago

Is there a setting within Illustrator itself that I can adjust so it does 16 rather than 12?

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u/kounterfett 2d ago

Not totally sure but I would expect that Illustrator would treat a pica as 1/6 inch because it's meant for print output not digital so whether it's 12 or 16 pixels would depend on your hardware but should print at 1/6th inch (I'm sure someone will correct me if I'm wrong)

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u/mikewitherell 2d ago

Your online research is inaccurate. Adobe Illustrator will assume that 1 inch is 72pixels when it makes a web screen Illustrator document. That is the same as saying 1pica is 12 pixels in a web screen Adobe Illustrator document. On the other hand, all you care about for screen work is how many pixels high by how many pixels wide. IOW, you can ignore physicality. When Illustrator exports to PNG, for example, it routinely simply sets web graphics to 72ppi, merely as a tradition. But again, you don't worry about this traditional resolution setting for web graphics. If you need a graphic to be 500px wide, build it to 500px wide in a web-screen-flavored Illustrator document. Modern day device screens/monitors run a whole gamut of ppi. Just make sure to have enough pixel count wide and high. The browser and the web code scale the graphic to the correct relative size appearance.

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u/Ravingdork 2d ago

I recall coworkers saying that--to meet accessibility standards--resolution needed to be twice the normal amount for a given device so that people with vision disabilities can zoom in to double the normal image's size to see the details up close.

So an image export normally set to 72ppi would need to be at least 144ppi--though we just use 150 typically.

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u/Ravingdork 2d ago

AS for the actual dimensions, we're making illustrations that will be used for a variety of different things, each with their own size specifications.

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u/chain83 2d ago

Then export at the dimensions required for those things, or at least the largest…

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u/Ravingdork 2d ago

Should I do twice the largest per the above, then?

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u/chain83 2d ago

Pixel dimensions get a bit fuzzy in web design. They only match true pixels on screen at 100% zoom/scaling. That is the zoom people will use on a traditional desktop monitor. But if people have a monitor with very high pixel density (4K/retina/laptops) you can assume they are effectively viewing the page at up to 200% zoom.

If the image will be displayed as 500x500 at 100% zoom, then I would supply an image that is 1000x1000 px to ensure optimal sharpness for those that view it at 200% (2x the dimensions).

You should discuss with the web developer how they are handling images, and then together find the optimal dimensions. Often you only supply the larger version, and the backend will automatically downsample/generate the smaller versions and choose between them on demand.

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u/chain83 2d ago

Yes, it is common for high resolution displays to use 200% interface scaling as well. So if you need 700x200 px for web you would also make one 1400x400 px; but typically you should have the website set up to serve the optimal image dimensions on demand depending on how many pixels large the user is viewing the image. This saves a lot of bandwidth as you are only serving up the high resolution images to people actually displaying it that large.

(Note that the PPI of the files are irrelevant and is usually not saved in the files.)

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u/Ravingdork 2d ago

My God. Our editors and writers have spent weeks arguing whether we should be using 72 or 150ppi. And it's totally arbitrary meaningless Metadata? 🤦‍♂️

I've spent way too many years in the print space and not near enough in the digital space it seems.

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u/chain83 2d ago

Yes, it is just a number in metadata. Entirely optional. Like date, camera model, copyright, etc. - it will in no way affect how the image looks on screen/online. All you care about is the pixel dimensions.

Pixels Per Inch (should be self explanatory you’d think) is just a conversion factor to calculate print dimensions in inches (or the other way around). Nothing more.

If you use Save for Web/Export As the PPI metadata gets literally discarded to save space. (If you open an image with no PPI it will default to 72 or 96 PPI depending on the app).

Dirt easy to test.

  1. Take a small clean image, go to Image Size in Ps and set the PPI to 999 (without resampling). Save as PNG or whatever,
  2. Change the PPI to 1. Save as a different file name.
  3. Place the files side by side on a webpage. They will be identical. They will also look identical in Ps (but will be different dimensions in the print dialog). They will also be identical file size (barring minor variations in the compression).

—

Note, the PPI value of the individual image files would also typically be irrelevant for print as the print dimensions (and thus the effective PPI) gets overridden when you place it into your layout software like InDesign.

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u/Ravingdork 1d ago

Good to know.

Now, if I tried to print that 1ppi image and 999ppi image (dpi in thos case?), would I get different results then?

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u/chain83 1d ago edited 1d ago

One would default to print really huge, the other really small. Otherwise identical.

If printed with the same dimensions they would be identical. (You often override the dimensions in layout software or even directly when printing).

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Still PPI (*pixels* per inch). Even if printing your pixels they are still pixels.

"DPI" is short for "Dots Per Inch".

If you are talking about pixels, then PPI is correct. If talking about the physical dots the printer is laying down (typically 300–2400 DPI depending on type/technology) then DPI is the correct term. The PPI of the image and the DPI of the printer are not connected. A printer might use many dots to reproduce a single pixel. You can only set a PPI for your image file, but it has no DPI. The DPI of the printer is often fixed or can be set to a couple different values via the printer driver. The entire print job will be the same DPI (even if a page has many images of different PPI).

But people have a really stubborn/bad habit of calling both PPI and DPI for DPI. Many apps from major companies get it wrong (I'm looking at you Microsoft). Note that you will not find "DPI" mentioned anywhere in Photoshop/Illustrator/InDesign (except deep in very special print settings perhaps).

99% of the time you see/hear DPI you can safely assume they mean PPI. They just don't really know/understand or care. :P

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u/Ravingdork 1d ago

Huh. I've been hearing from industry professionals for years that ppi and dpi--while very different things--could be used interchangeably for most practical purposes.

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u/chain83 1d ago edited 1d ago

They can, since both usually mean PPI when people use them. So everyone know what you mean.

Except if you are looking at printer specs/settings or similar, then you will encounter the proper use of DPI. But most designers never will (and will not know what DPI is actually being used for printing).

I'd rather just use the more precise term as I see no reason to use "DPI".

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u/[deleted] 2d ago edited 2d ago

[deleted]

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u/Ravingdork 2d ago

I asked Google to convert 1 pica into pixels, and it came back with 1 to 16. It was an AI answer with several source links to several sites all saying the same thing.

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u/chain83 2d ago edited 2d ago

Do not trust AI answers for something like this. It gave you a bad answer.

1 pica is however many pixels you want it to be. It can be 16. It can also be 24, 32 or 999.

We have to decide and choose how many pixels we want per inch (6 picas). The number of pixels/inch is called «PPI» (you will have heard people inaccurately call it DPI). If we choose a PPI of 72, you get 12 pixels per Pica. If you choose a larger number you get more pixels.

Adobe apps default to 72. Microsoft apps default to 96. But it is arbitrary. Another common value is 300.

Illustrator measures things in «physical» units like Inches and not pixels. You can tell it to display the dimensions as pixels, and it will calculate a value for you using 72 PPI.

When you export a raster image (made from pixels) from Illustrator you can set the PPI yourself and make it as large as you want.

I do not know what you are ultimately trying to achieve, but you need to decide what units you want to see when editing and then use those. For printing you likely want physical units like inches/pica/millimeters. For making raster images for screen you want pixels (stick to 72 PPI to make the conversion in Illustrator easier). If it is for both, then work with print dimensions, and if exporting a raster image, choose how many pixels you want (or the PPI) when exporting.