Comments on: The Myth of DPI http://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/ Web Design Resources and Tutorials Sat, 11 Feb 2012 03:33:00 +0000 hourly 1 http://wordpress.org/?v=abc By: joelhttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-647955 joel Tue, 25 Jan 2011 12:57:12 +0000 http://www.webdesignerdepot.com/?p=15412#comment-647955 anyone develop sites at super high res? helps when fleshing out details also when printing for portfolio pieces... i'd love to hear some feedback from the community on this topic. anyone develop sites at super high res?
helps when fleshing out details also when printing for portfolio pieces…
i’d love to hear some feedback from the community on this topic.

]]> By: Mike "Pomax" Kamermanshttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-614412 Mike "Pomax" Kamermans Tue, 30 Nov 2010 08:11:56 +0000 http://www.webdesignerdepot.com/?p=15412#comment-614412 Hi Ben,a small misconception in the article: while GIF discards dpi information (it's a screen only format with implied dpi value of 72, back when the monitor resolution was still assumed to be 72, rather than today's assumed 96), PNG most definitely allows for real print size information. Hit up Photoshop, make a new 2" x 4" x 123DPI image, save it to PNG and then open it in irfanview. Hitting 'i' for the file information will inform you that this image is indeed 2" by 4", computed from the DPI value stored in the PNG header.Now for the slightly more technical bit... PNG does not actually store "dots per inch", but instead stores physical dimensions as "pixels per meter", stored in the "pHYs" table of the PNG header. While this is an optional table that can be omitted for screen-only graphics, it is essential for dual media graphics, and for the sake of not misrepresenting PNG I'd highly advise you do a quick edit on the article to state that PNG is in fact perfectly suited for graphical contexts in which images having real physical dimensions matters.I know I personally rely on it heavily, because using PNG means I don't have to turn my graphics into JPG, which cannot be further edited for print due to unpredictable artifacting, or the much bulkier TIFF. Hi Ben,

a small misconception in the article: while GIF discards dpi information (it’s a screen only format with implied dpi value of 72, back when the monitor resolution was still assumed to be 72, rather than today’s assumed 96), PNG most definitely allows for real print size information. Hit up Photoshop, make a new 2″ x 4″ x 123DPI image, save it to PNG and then open it in irfanview. Hitting ‘i’ for the file information will inform you that this image is indeed 2″ by 4″, computed from the DPI value stored in the PNG header.

Now for the slightly more technical bit… PNG does not actually store “dots per inch”, but instead stores physical dimensions as “pixels per meter”, stored in the “pHYs” table of the PNG header. While this is an optional table that can be omitted for screen-only graphics, it is essential for dual media graphics, and for the sake of not misrepresenting PNG I’d highly advise you do a quick edit on the article to state that PNG is in fact perfectly suited for graphical contexts in which images having real physical dimensions matters.

I know I personally rely on it heavily, because using PNG means I don’t have to turn my graphics into JPG, which cannot be further edited for print due to unpredictable artifacting, or the much bulkier TIFF.

]]> By: Stony101http://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-599211 Stony101 Thu, 07 Oct 2010 17:34:58 +0000 http://www.webdesignerdepot.com/?p=15412#comment-599211 Great article.. Can anyone answer me this - its kinda related...I've just done a screen grab of an exiting website and measured its width. I use a mac.My colleague has just done the same on his pc.We get different pixel dimensions for the same onscreen elements - including images. The width of the site is about 80px shorter on mineWhat's this about? Great article.. Can anyone answer me this – its kinda related…

I’ve just done a screen grab of an exiting website and measured its width. I use a mac.

My colleague has just done the same on his pc.

We get different pixel dimensions for the same onscreen elements – including images. The width of the site is about 80px shorter on mine

What’s this about?

]]> By: Luis Suárezhttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-598159 Luis Suárez Fri, 01 Oct 2010 00:13:55 +0000 http://www.webdesignerdepot.com/?p=15412#comment-598159 Excellent reading.Cheers!Luis S. Excellent reading.

Cheers!

Luis S.

]]> By: Music Tubehttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-584165 Music Tube Sun, 20 Jun 2010 20:55:40 +0000 http://www.webdesignerdepot.com/?p=15412#comment-584165 Very interesting article, learned alot new, especially in the part about "72". Thanks! Very interesting article, learned alot new, especially in the part about “72″. Thanks!

]]> By: Mark Astlehttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-583012 Mark Astle Fri, 11 Jun 2010 06:00:14 +0000 http://www.webdesignerdepot.com/?p=15412#comment-583012 Because the physical size of the image doesn't change. Unless you print it out. In which case, each increase in DPI would make the image smaller in mm. If you keep it to, say 1 inch square, and change the DPI, the size and quality of the image will change. Which should all be obvious stuff really.I think you're kind of right, it's just the title of the article that's got people talking, and I guess that was the idea. Because the physical size of the image doesn’t change. Unless you print it out. In which case, each increase in DPI would make the image smaller in mm. If you keep it to, say 1 inch square, and change the DPI, the size and quality of the image will change. Which should all be obvious stuff really.

I think you’re kind of right, it’s just the title of the article that’s got people talking, and I guess that was the idea.

]]> By: Julian Krispelhttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-583000 Julian Krispel Fri, 11 Jun 2010 04:53:30 +0000 http://www.webdesignerdepot.com/?p=15412#comment-583000 I love this discussion. Seems as though the commenteers have very little of what you're saying Mister Gremillion. I love this discussion. Seems as though the commenteers have very little of what you’re saying Mister Gremillion.

]]> By: Ben Gremillionhttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-582973 Ben Gremillion Fri, 11 Jun 2010 00:42:07 +0000 http://www.webdesignerdepot.com/?p=15412#comment-582973 That's the point: Changing DPI alone has negligible impact on a web image's file size and none on its dimensions. @bob said that "There is actually a huge difference between an image of 300 x 300 pixels saved at 72dpi, to one saved at 300dpi." Yet the images I saved had very little difference -- if I left the pixel count the same. That’s the point: Changing DPI alone has negligible impact on a web image’s file size and none on its dimensions. @bob said that “There is actually a huge difference between an image of 300 x 300 pixels saved at 72dpi, to one saved at 300dpi.” Yet the images I saved had very little difference — if I left the pixel count the same.

]]> By: Mark Astlehttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-582969 Mark Astle Thu, 10 Jun 2010 22:26:25 +0000 http://www.webdesignerdepot.com/?p=15412#comment-582969 If you're not resampling the image, of course the image size and pixel size will stay the same. If you change the dpi but keep the actual image size in mm the same, then it changes. I'm not sure what yo've just proved? If you’re not resampling the image, of course the image size and pixel size will stay the same. If you change the dpi but keep the actual image size in mm the same, then it changes. I’m not sure what yo’ve just proved?

]]> By: Ben Gremillionhttp://www.webdesignerdepot.com/2010/02/the-myth-of-dpi/#comment-582946 Ben Gremillion Thu, 10 Jun 2010 16:52:01 +0000 http://www.webdesignerdepot.com/?p=15412#comment-582946 This being a blog and an article about web design, I assumed it was clear that the article was not about print. My mistake.Could you provide some examples of images with different DPI settings but the same number of pixels? In my tests, changing 72 DPI JPG to 300 DPI, and later 4000 and 10000, only increased the file size by less than half of one percent.I just created a new file and saved it at different DPI after disabling "Resample Image" in Photoshop's Image Size box.300x300 @ 36 DPI was 21,118 KB 300x300 @ 72 DPI was 21,118 KB 300x300 @ 300 DPI was 21,120 KB 300x300 @ 900 DPI was 21,120 KB 300x300 @ 4000 DPI was 21,122 KB 300x300 @ 8000 DPI was 21,122 KB 300x300 @ 10000 DPI was 21,124 KB 300x300 @ 20000 DPI was 21,124 KBEach image used image quality 6 in Photoshop's "Save As" command. I didn't use "Save for Web" because that removes DPI information from the file.The files gain two bytes for every digit in the DPI measurement itself. @Julian noticed this difference, and @snlr guessed that it's a rounding error or 16-bit character. Either way, the size difference between several orders of magnitude with the same compression and number of pixels is well under 1%.How much savings did you get in your tests? Also, how did you determine that I'm a goose and not a gander? This being a blog and an article about web design, I assumed it was clear that the article was not about print. My mistake.

Could you provide some examples of images with different DPI settings but the same number of pixels? In my tests, changing 72 DPI JPG to 300 DPI, and later 4000 and 10000, only increased the file size by less than half of one percent.

I just created a new file and saved it at different DPI after disabling “Resample Image” in Photoshop’s Image Size box.

300×300 @ 36 DPI was 21,118 KB
300×300 @ 72 DPI was 21,118 KB
300×300 @ 300 DPI was 21,120 KB
300×300 @ 900 DPI was 21,120 KB
300×300 @ 4000 DPI was 21,122 KB
300×300 @ 8000 DPI was 21,122 KB
300×300 @ 10000 DPI was 21,124 KB
300×300 @ 20000 DPI was 21,124 KB

Each image used image quality 6 in Photoshop’s “Save As” command. I didn’t use “Save for Web” because that removes DPI information from the file.

The files gain two bytes for every digit in the DPI measurement itself. @Julian noticed this difference, and @snlr guessed that it’s a rounding error or 16-bit character. Either way, the size difference between several orders of magnitude with the same compression and number of pixels is well under 1%.

How much savings did you get in your tests? Also, how did you determine that I’m a goose and not a gander?

]]>