Image resolution, the pain in my...brain!

I've been a Graphic Designer for around 20 years and this week I heard a term that I hadn't come across before (at least not that I remember). Samples per inch (SPI) the term came from a communication with a British publication I was sending a cover image for their magazine.

DPI, PPI, SPI; could image resolution be any more complicated. For those who don't know, DPI stands for Dots-per-inch, PPI, pixels-per-inch and SPI Samples-per-inch.

I'm not vain enough to think I know everything in my industry, but I know quite a bit and I had never heard of SPI before, so I did what anyone would do, I looked it up on the internet. I found the following definition on Wikipeadia.

Samples per inch (SPI) is a measurement of the resolution of an image scanner, in particular the number of individual samples that are taken in the space of one linear inch. It is sometimes misreferred to as dots per inch, though that term more accurately refers to printing resolution. Generally, the greater the SPI of a scanner, the more detailed its reproduction of the scanned object.
Typical consumer-level flatbed scanners are capable of optical resolution ranging from 100 to 2400 SPI; high-end scanners may have an optical resolution of 4800 SPI or more. Many scanners use interpolation techniques to achieve a higher effective SPI rating, with some manufacturers offering nearly one million SPI, though the quality is primarily limited by the optical resolution; interpolated SPI does not provide additional pixels in the scanned image.
Horizontal and vertical SPI ratings may differ for a given scanner; typical flatbed scanners use a horizontal array of sensors that are passed across the bed using an electric stepper motor. The density of the array of sensors determines the horizontal scanning resolution, while the minimum step size of the motor determines the vertical resolution. Similar characteristics are present in drum scanners, which continuously spin the item being scanned past the sensor array for numerous imaging passes.
To calculate the number of raw data bytes that a scanned image will take up, you can use the follow formula :
Where : vSPI is the vertical SPI hSPI is the horizontal SPI (can be considered the same as vSPI if not specified specifically) area is the squared area of the scanned document in inches²
color depth encoding is the number of bits used to encode a given amount of color information (256 colors=8; 65'536 colors=16; 16million colors=24)
Remember that this will give raw data bytes, images are almost always compressed when saved to disk using lossless (like PNG, TIFF) or lossy image formats (like JPEG).
That is understandable to me, but not to most people, and most of the scanners that I've owned don't have the SPI measurement at all. Most have DPI but that isn't the same as SPI.

DPI stands for dots-per-inch. This is primarily a printing term standing for the number of halftone dots within an inch. The more DPI you have, such as 300 dpi, the better quality of image you have on the printed page. Most scanners have this measurement when you scan in an image.

PPI stands for Pixels-Per-Inch. PPI is the screen resolution or resolution you see on your monitor. In general PPI and DPI are used interchangeably although they don't mean the same thing. 300 ppi is close enough 300 dpi so it makes little difference when scanning. If you notice your scanner probably says dpi and when looking at it in Photoshop it shows ppi. When creating an image for the internet 72 ppi is generally the accepted measurement.

I explain all this to my students and they look at me like I just grew horns out of the top of my head. To make it more difficult for them to understand, the resolution you are using needs to be the dpi, ppi. spi at the size you will be using the image. For example, if you have a space in your brochure that is 4 inches wide, you need your image to be 300 dpi, ppi at 4 inches wide. If you are putting an image on the web at 600 pixels wide then you need your image to be around 72 ppi, dpi at 600 pixels wide.

Onscreen graphics don't need to be as hi-resolution as graphics that are going to print. This is the reason you can't get a great quality print from an image that is optimized for the web.

The rule-of-thumb I teach is, you can always scale something smaller but you shouldn't scale bigger than the original resolution, if you do you will lose image quality.

As far as Samples per inch goes, I'm doing what I always done. Scan or shoot my digital images at the ppi or dpi that I need, and not worry about SPI until someone brings it up again.

©2010 Michael Burke

Why Be A Teacher?

I was asked the other day if I enjoyed being a teacher (I'm an adjunct professor at the University of Central Oklahoma). I replied, "I really enjoy teaching". Then the student asked me why did I start teaching, after all I have a successful small graphic design business and with an 11 month old baby, I have little time for anything else. I answered him by saying, "I enjoy passing on what I have learned".

That was a fairly simple answer to the question and it doesn't completely explain why I'm teaching. So I thought I would try to provide better rational.

When I first applied to teach at UCO, I wish I could say I was being a great humanitarian and wanted to give back. But the truth is, I was almost broke. My business had been doing poorly and I thought I would have to take a job as a bag boy at the local grocery store.

I started to think, what would I do if I couldn't do what I do? I'm only really trained at one thing and that is graphic design, so I sat down to solve my problem (after all that's what designers do, solve problems).

I thought a lot about my skills and experience and came up with…nothing!

Well, not quite absolutely nothing, but I didn't want to work in a restaurant or work behind a register, and an insurance salesman was out of the question!

So I did what I do when I design something. I got out a pencil and paper and started doodling and making notes. What I came up with was a small list of different occupations.

Designer (doing that now)
Electrician (already done that)
Farmer ( HELL NO! did that when I was a kid)
Banker ( nope I'm an artist which means I can't add or spell)
McDonald's (wont shave my beard, so that one's out)
Teacher (hold on a minute!)

Teacher…could I really do that? Really? I had absolutely no experience, just 18 + years of experience in the Advertising and Graphic Design industry.

But I thought what the heck. So I sent my resume to UCO and called a couple of people I still knew still worked there to let them know I was applying.

About a year later I got a call to come in for an interview. By this time my business had recovered and I didn't need the extra income. I also enjoy my off time with my family. So why would I want to take on another job?

As I sat down to think about it and talk it over with my wife when a thought hit me. I realized some of the most influential people In my life were teachers.

Some teachers taught me specific skills and some taught by example and I realized I very much wanted to be that kind of person to others!

The following teachers are examples of some of the people that made a difference in my life.

Mr Shores, high school algebra: Not only taught me math, but also taught me to respect others. He would never call anyone by their first name, it was always Mr. Burke or sir and a handshake when you came to class.

Mrs. Kanaga, typing teacher: Thank God I learned how to keyboard!

Mrs. Bamberg, english teacher: Taught the value of reading everything.

Mr. Henderson, Vocational Ag teacher: Taught everyone in his class to accept responsibility for your own existence and your own actions.

My oral communications teacher in college: I cant remember his name but he taught me to read at least four papers a day. He said it is our responsibility as responsible adults to keep informed on current events.


Jim Watson, Graphic Design Teacher: Jim taught me to question everything, that designers solve problems and also as communicators we need to communicate a rational for everything we do.

Which leads me back to my topic. Why be a teacher?

I'll tell you why. Aside from a paycheck, I want to make a difference in the way young people look at life. Make them stop and think a moment. Live life to its fullest, don't just exist! Every teacher I've had taught me something that has stayed with me all my life.

I don't want students to look back and say, Mr. Burke was a great teacher. I want them to go out, take what they have learned in my classes, then use the information to become productive and successful people, then pass it on.

My teachers were a big influence on me and I want to take this opportunity to say thank you to all of them.

I'm very proud to be a teacher and I'm doubly proud of all my students present, and past!

Learn something and pass it on, be a Teacher! You won't regret it.