Egg Freckles

Fri 10/28 Counting Pixels

When I was in the forth grade I was diagnosed with Leber’s hereditary optic neuropathy, a genetic condition that leads to the acute onset of visual loss in one or both eyes. Today I am legally blind. I have a central visual acuity of 20/200 in my best eye while wearing prescription eyeglasses. This means I see approximately one-tenth of the detail a person with normal vision sees at the distance of 20 feet. As an object is brought closer to me I can see it more clearly, but I must strain to do so. When sitting in front of a computer my face is inches from the screen. When I was in grade school other kids would mock me by asking if I was “counting the pixels,” the smallest bits of information on a computer display. My vision has never improved, it has only gotten worse. I cannot drive. I have a hard time recognizing people on the street, and although I do not walk into things, it is difficult going through life knowing I am missing so much of the world around me.

Computers have always been a great equalizer for me. On a computer I can do anything a person with normal sight can do as long as the image is large enough for me to see. When I first began using computers having a large screen was important, but as computer monitors have increased in size the amount of information packed into each display has also increased making the picture smaller and harder for me to see¹. Now I must move my head to take in the entire picture on screens larger than 22 inches, and the predominance of wide aspect ratios has only made my problem worse. One solution is to decrease my display’s resolution making the image larger while reducing the amount of information displayed on the screen. This technique worked well on CRT monitors where there is no native resolution, but modern digital monitors, like LCDs, lose their sharpness when the image being displayed is less than the maximum resolution. Another solution is to keep the display’s resolution at the maximum setting preserving sharpness, but increasing the content’s font size so that it is more readable². This technique allows me to get my work done, but I still have to strain my eyes and move my head when manipulating the GUI. I have endured a mixture of both these remedies ever since I got tired of squinting at my Mac’s high resolution monitor, but I would prefer a solution that would allow me to see everything on my display all at once with the maximum sharpness available.

Resolution independence is a feature that allows for a computer’s display to be scaled independently of the screen’s resolution. You might already have experienced resolution independence by using the zooming feature on a modern web browser. Operating systems that offer resolution independence are very rare because until now only special applications like medical imaging required the use of high resolution monitors³: that make resolution independence a necessity. Starting with Mac OS X 10.4 Tiger Apple began dabbling with resolution independence. Through the use of Quartz Debug, a developer utility, a user could increase the scale of the user interface enlarging everything on the screen without losing sharpness. This made the picture easier to see, but not all applications were ready for arbitrary scaling. Low resolution bitmap graphics would appear pixelated when scaled up, and the layout of some applications broke all together. It would take until Mac OS X 10.7 Lion for Apple to change their user interface scaling strategy and introduce a new Quartz Debug utility with HiDPI.

HiDPI is not resolution independence. It takes the on-screen elements and upscales them by a factor of two in both directions. This makes everything on the screen appear twice as large but without losing sharpness inherent with reducing the resolution on a digital display. In order for HiDPI to work properly applications need to contain high resolution bitmap graphics that are 2x the intended size. Vector illustrations and type require no modifications and can be scaled to any size without losing sharpness⁴. The display needs to have a maximum resolution four times larger than the desired working resolution. A 2560 by 1440 Thunderbolt Display will have a 1280 by 720 usable working resolution when HiDPI is enabled⁵. HiDPI is easier for a computer to perform than resolution independence because the scale of the resolution is always divisible by two and not some user specified arbitrary value. Apple first used HiDPI with the iPhone 4’s Retina display. At 960 by 640 the iPhone 4’s 3.5 inch display offers four times the usable screen resolution than previous iPhones with the same size display. Elements on the screen should appear smaller on the iPhone 4, but because of HiDPI everything has been scaled by a factor of two and readability and sharpness are increased.

For most people HiDPI is a feature for the future when displays are over four times the resolution they are today. For me HiDPI is a feature I use today. I am still counting pixels, but instead of straining to see the information on the screen I am enabling HiDI, scaling my computer’s resolution by two, and enjoying the sharpness I lack in the rest of my life.