PPI/DPI setting... why do you want it?
I occasionally see requests for a PPI/DPI setting in Aperture and I just noticed a request for the same in the discussion about Adobe's Lightroom. I've posted comments about why a PPI/DPI setting is not needed, so I'm curious to see if maybe I'm missing something and I'd like to hear some feedback on the subject to help educate myself and others along the way. If my examples aren't exactly clear and seem confusing, perhaps someone else can explain what I'm saying in a much more elegant and easier understood way.
Here's a copy of my original post about the subject. I've added a few other examples for further clarification on pixel dimensions in relationship to output.
"An output ppi/dpi setting is not necessary and not relevant and here's why...
Remember, were talking about pixels here, not inches. Pixel dimensions are all that matter when it comes to sizes in digital photography.
So when you export an file from Aperture and want something different from the built-in presets, choose "Edit" from the "Export Preset" pop-up in the Export dialog box. You can then add your own settings based upon the output pixel dimensions you would like to have.
For instance, if you need an 8 x 10 inch image, then take whatever ppi/dpi you would like and times it by those dimensions. A common standard for the web is 72ppi, so your pixel dimensions for an 8 x 10 inch image will be 576 pixels x 720 pixels. A common standard for printing is 300dpi, so then an 8 x 10 inch image will need to be 2400 pixels x 3000 pixels.
Hence, say you have a 2400 pixel x 3000 pixel file, it would equal...
- 8 x 10 inches @ 300 ppi
- 33.333 x 41.667 inches @ 72ppi
- 4 x 5 inches @ 600ppi
- 10 x 12.5 inches @ 240ppi
- 2400 x 3000 inches @ 1ppi
All the above listed dimensions will give you the exact same perfect 8 x 10 inch print from a 300dpi printer. In fact, whatever the dpi of the printer, each of the above listed dimensions will print the same size on the same printer.
Say you gave your favorite printer a file that another image editing application (Photoshop perhaps) says is 33.333 x 41.667 inches @ 72dpi or any of the other combinations I listed above. Well most printers are set to print at 300dpi, so it would output perfectly as an 8 x 10 inch print. If the printer was set to print at 360dpi, then you would have a perfect 6.667 x 8.333 inch print.
Again, if you need an 8 x 10 inch print and the printer prints at 300dpi, then you need a 2400 x 3000 pixel file, if you need a 16 x 20 inch print, and the printer prints at 300dpi, then you need a 4800 x 6000 pixel file. If the printer prints a 240dpi, then an 8 x 10 inch print would need to be 1920 pixels x 2400 pixels and a 16 x 20 inch print would need to be 3840 pixels x 4800 pixels.
So, you see, it doesn't matter what you ppi/dpi is, it can be anything you want it to be. The only thing you need to know is what you want your pixel dimensions to be and choose those based upon what your output device is."
-Robert
PowerMac G5 Quad 2.5Ghz Mac OS X (10.4.3) 4.5GB RAM, Nvidia 7800 GT, 600GB RAID
Here's a copy of my original post about the subject. I've added a few other examples for further clarification on pixel dimensions in relationship to output.
"An output ppi/dpi setting is not necessary and not relevant and here's why...
Remember, were talking about pixels here, not inches. Pixel dimensions are all that matter when it comes to sizes in digital photography.
So when you export an file from Aperture and want something different from the built-in presets, choose "Edit" from the "Export Preset" pop-up in the Export dialog box. You can then add your own settings based upon the output pixel dimensions you would like to have.
For instance, if you need an 8 x 10 inch image, then take whatever ppi/dpi you would like and times it by those dimensions. A common standard for the web is 72ppi, so your pixel dimensions for an 8 x 10 inch image will be 576 pixels x 720 pixels. A common standard for printing is 300dpi, so then an 8 x 10 inch image will need to be 2400 pixels x 3000 pixels.
Hence, say you have a 2400 pixel x 3000 pixel file, it would equal...
- 8 x 10 inches @ 300 ppi
- 33.333 x 41.667 inches @ 72ppi
- 4 x 5 inches @ 600ppi
- 10 x 12.5 inches @ 240ppi
- 2400 x 3000 inches @ 1ppi
All the above listed dimensions will give you the exact same perfect 8 x 10 inch print from a 300dpi printer. In fact, whatever the dpi of the printer, each of the above listed dimensions will print the same size on the same printer.
Say you gave your favorite printer a file that another image editing application (Photoshop perhaps) says is 33.333 x 41.667 inches @ 72dpi or any of the other combinations I listed above. Well most printers are set to print at 300dpi, so it would output perfectly as an 8 x 10 inch print. If the printer was set to print at 360dpi, then you would have a perfect 6.667 x 8.333 inch print.
Again, if you need an 8 x 10 inch print and the printer prints at 300dpi, then you need a 2400 x 3000 pixel file, if you need a 16 x 20 inch print, and the printer prints at 300dpi, then you need a 4800 x 6000 pixel file. If the printer prints a 240dpi, then an 8 x 10 inch print would need to be 1920 pixels x 2400 pixels and a 16 x 20 inch print would need to be 3840 pixels x 4800 pixels.
So, you see, it doesn't matter what you ppi/dpi is, it can be anything you want it to be. The only thing you need to know is what you want your pixel dimensions to be and choose those based upon what your output device is."
-Robert
PowerMac G5 Quad 2.5Ghz Mac OS X (10.4.3) 4.5GB RAM, Nvidia 7800 GT, 600GB RAID
