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Rulers best in pixels?

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  #1  
Old 07-19-2009, 06:38 AM
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Rulers best in pixels?

I just listened to a Deke podcast when he mentioned in passing that rulers were better measured out in pixels. I have always used inches, and am wondering why pixels would be better.
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Old 07-19-2009, 09:50 AM
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Re: Rulers best in pixels?

Pixels are absolute. They represent the number of elements in an image. "Inches" is a relative term to represent how those pixels are displayed or printed. If change thedimensions of the image (inches) with the resampling box unchecked, you just change the resolution but the number of pixels remain the same. So using pixels is not necessarily better - more a matter of ease and preference. However it is for many people a more convenient way to always keep in perspective the physical assests that you are dealing with in an image. Working only in inches / cm can, it may be easier to make an error and resize an image and end up losing image data or manufacturing data that was not there (Upsampling).
Regards, Murray
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Old 07-19-2009, 12:10 PM
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Re: Rulers best in pixels?

Hi Murray, thank you. That was helpful. Given my pathetic lack of arithmetic skills I went off and experimented with all the permutations in the dialogue box with "image resize". I saw what you meant by pixels being absolute. To be honest it's the first time I've really had a grasp of what resampling is, versus what happens if you fiddle around with the resampling box unticked. It was a useful exercise.

I've now changed my rulers to pixels. Thank you again :-)
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Old 08-06-2009, 06:42 PM
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Re: Rulers best in pixels?

Well yeah, screen is made by pixels, not inchs or the like. That's because the pixel aspect ratio.
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Old 08-07-2009, 05:33 AM
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Re: Rulers best in pixels?

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Originally Posted by Quantum3 View Post
That's because the pixel aspect ratio.
No, that has nothing to do with this. Pixel aspect ratio is for when you are creating images for output on something that doesn't use square pixels (e.g. traditional TV broadcasts).

Anyway, I personally use pixels as well, as I've never had anything useful to measure in inches/cm using those (the only time i really use that measurement is when i pop up the image size dialogue to check it at specific PPI settings to gauge how large I can print it). Pixels are the only unit that makes sense when working for screen, and I do that quite often.
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Old 08-07-2009, 04:41 PM
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Question Re: Rulers best in pixels?

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Originally Posted by Chain View Post
No, that has nothing to do with this. Pixel aspect ratio is for when you are creating images for output on something that doesn't use square pixels (e.g. traditional TV broadcasts).

Anyway, I personally use pixels as well, as I've never had anything useful to measure in inches/cm using those (the only time i really use that measurement is when i pop up the image size dialogue to check it at specific PPI settings to gauge how large I can print it). Pixels are the only unit that makes sense when working for screen, and I do that quite often.
Yeah, I know that. But I think there is a difference between 1 inch and 1 pixel, or between 1 centimeter and 1 pixel, or somehow PS accurately fits centimeters along/into pixels?
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Old 08-07-2009, 07:13 PM
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Re: Rulers best in pixels?

one isn't any better than the other... if you're preparing files for print and need to make sure you have enough bleed or whatever you're not gonna measure that in pixels. or if you're dealing with pixel dimensions for a website or something then you measure in pixels... it has completely different applications and one is certainly not better than the other.
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Old 08-08-2009, 02:56 AM
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Re: Rulers best in pixels?

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Originally Posted by Janko View Post
one isn't any better than the other... if you're preparing files for print and need to make sure you have enough bleed or whatever you're not gonna measure that in pixels. or if you're dealing with pixel dimensions for a website or something then you measure in pixels... it has completely different applications and one is certainly not better than the other.
I expressed my self wrong. I meant image pixels matchs the screen pixels but what about centimeters or inches?
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Old 08-08-2009, 06:33 PM
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Post Re: Rulers best in pixels?

That's what PPI (often referred to as "DPI") means. It's the print resolution of your image.

PPI = pixels per inch.
In other words, how many pixels there should be per inch (when printing).

If you go to image->image size, and uncheck "resample image", then you can type in different PPI (resolution) values and see how that affects your image size. This will also affect the scale of the rulers if set to show inches/cm.
Note that the actual image (the pixels) are unchanged so we are just saying how large we intend to print it.

To get an idea of the quality here is some sample values (not set in stone):
300 ppi = top quality print (glossy magazine, photo, etc.) for viewing up close.
200 ppi = lower limit for what will look good up close.
100 ppi and below = will not look good up close, but works if viewed further away (think a photo on a large poster - not for viewing up close).

---- edit: ----
As a side note:
The size of the pixels on the screen (in inches/cm) differs from monitor to monitor. My monitor can fit about 96 pixels in an inch, but my large LCD TV fits far fewer. So if you tell someone your digital image file is "1 inch" large on your monitor that sais nothing about the actual size and quality.

If you are preparing images for high quality print (e.g. a magazine), you could state your image size as 40 by 30 cm at 300 ppi. That would relay how large they could print it at max quality (without them having to calculate it from the pixel values).

If you are preparing images for screen use (e.g. a website), you would always state the image size in pixels (as there is no need for print resolution - because it's not going to be printed)

Last edited by Chain; 08-08-2009 at 06:42 PM.
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Old 08-08-2009, 09:25 PM
Quantum3 Quantum3 is offline
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Re: Rulers best in pixels?

Mmmhhh... I got wrong again.

I'm asking about the match between pixels and centimeters (I don't know what about inches). On screen, measurements are relative, but I'm sure a pixel is a totally different measurement escale meaning that 1 centimeter is not equal to 1 pixel the same as 1 pixel of a Plasma TV is not equal to a Computer Screen pixel because the aspect ratio of each one of those. So I think the same happens between centimeters, inches and pixels and that's why the photoshop ruler works better in pixels, because the screen, I suppose. I don't know if that's correct, but I suppose it's.

PS: It's unconfortable for me when goodwill people spend lot of time and words replying something it wasn't asked, I don't know what to say when that happens
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