My understanding is that images displayed on websites need to balance quality with file size. I have been lead to believe that most screens or browsers only display 72 px/inch. This confuses me especially when there are new mobile devises that say they are high resolution or use a Retina display. Also, as soon as these devises are available there is an outpouring of upgraded apps saying they updated their graphics for the new displays. My questions are these:
- Do browsers or screens really only display a maximum of 72 px/in?
- Do these new hardware products require higher resolution images on a site to look good?
- What resolution is best used for a photo gallery on a site?
- What is the difference, if any, between the two resolutions (image and hardware pixels)
I ask because I am working on putting my photographs online and would like them to be displayed at their fullest potential.
Thank you.
You are correct in that there needs to be balance between quality and file size.
Your questions:
1. You do not have a clear understanding of what px/inch means, and it's a really common thing to not grip.
Anyhow. If "screens" could only display a maximum of 72 px/in, then there would have to be a standard for how many pixels you are "allowed" to display on a screen of a certain physical size in inch, right? Example: An iMac 27 screen is 27 inches and has a resolution of 2560x1400 pixels. That gives a certain number of pixels per inch, (109 to be exact) defined by the physical size of the screen and what resolution it's running at. The PPI value is just a resulting value of resoluion vs physical screen size. Retina is just a marketing term for Apples screens with a PPI value so high that the eye cannot distinguish individual pixels.
Wikipedia article:
http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density
DPI/PPI calculator:
http://members.ping.de/~sven/dpi.html
2. I think Apple devices scale content really well, so it's not necessary. However, ideally, you would have your images ready at a 2048x1536 so they could be displayed pixel perfect on a Retina iPad.
3. Generally you have thumbnails, previews and then maybe large resolution versions of your photos. Usually something around 2 Mpix has been considered plenty, as that's what most screens can display. Look for 'responsive web design' when you make a site, that will make it ready for all devices.
4. On the difference between 'hardware' and 'image' pixels. The resolution of a digital image is ONLY defined by the amount of pixels in it. A high pixel count doesn't necessarily mean high quality though. Further, if you set an image to a DPI/PPI value is completely irrelevant as long as you're keeping it digital, cause obviously, you can't affect what physical size anyone's gonna view your content at, right? You can't decide that a picture's gonna be 250 PPI on anyones screen, cause that's defined by the resolution and physical size of that screen, as stated above.. you with me?
If this was possible, then you could send a picture to someone with a low PPI, and then that picture would take control of their computer and lower the resoluion to display it at the set PPI. Not a great scenario, eh?
When printing however, you need to consider the DPI, but that's a whole different matter.
I hope this helps. Understanding this will make working with picures a whole lot less confusing.