I guess I should start with a brief introduction: I retired after 37 years at the State University of NY at Oswego Theatre Department. While there I maintained the electronic systems for the department, and developed & taught courses in sound design, electronics, special effects & photography. I enjoy traveling, working with the Red Cross Disaster Services, and building & maintaining Lakeshore Images, my Photography & RV Information web page.
Alright, that done let’s talk photography:
How important is the “Pixel Count” of the sensor in my camera? The term is a count of the number of individual sites on your camera’s sensor that convert light to an electrical signal. The larger the number, the higher the resolution image your camera can produce. Digital cameras range from as few as .3MP for many of the early (1994) consumer digital cameras produced by Apple, Olympus & Casio to 39MP for the current $33,999.00 Hasselblad medium format DSLR.
When I first considered discussing the megapixel count of cameras, it seemed fairly important, but after reviewing a number of ads in both my local newspapers & a couple of magazines, I found that it has become difficult to purchase a camera with less than 6 megapixels. Since I have managed (although not straight out of the camera) to print a usable 20″X 30″ image from my Coolpix 995, a 3.34 megapixel camera, it looks like almost anything you buy will have plenty of resolution. Fortunately, what is “usable” in an enlargement covers quite a range. The viewing distance, the type of printer & printed material as well as the software used to make the enlargement all contribute to how usable the final print will be. In the case mentioned above, the 20″X 30″ photograph was part of a lobby display – no one could get closer than 10′ so the relatively low resolution was not a problem.
For most reasonable size prints, a 6 – 8 MP camera will satisfy the casual photographer; the professional photographer will always want a higher pixel count than what he or she owns!
So, simple answer – Almost any modern digital camera will have a sensor capable of producing a good quality enlargement or an excellent image on almost any size computer screen.
If you are interested in more information about spreading pixels across different media, click on “Read the rest of this entry.”
I am very interested in feedback, both on the articles I’m posting as well as suggestions for future postings. Please contact me with your suggestions!
Since some of us still have older cameras, and others may want to reduce the number of pixels in an image to make it easier to email or store, it might be worth discussing how much resolution you need to do different things with your image.
First, I would always save my original images at the highest resolution possible. You never know what you may want to do with an image in the future; nothing will annoy you more than getting a request from someone asking for a large print or worse yet, someone willing to pay for a high resolution version of an image for which you only have a low resolution version available.
Rather than always using the full resolution for every use, it is practical to resize the image to match the media you will use to display it. The first thing to consider is the size of the final image. While a 640 X 480 pixel image (multiply the two numbers together to get the megapixels, in this case about .3MP) will be fine to produce a small print or image on a web page, spreading the same number of pixels across a 20″X 30″ poster will make each so large they become visible as individual dots.
You also need to determine the resolution of the media you will use to display your image. There isn’t any advantage to using more resolution that your media can display – it just makes your file larger. Computer monitors originally used 72 dpi (dots or pixels per inch) for Macintoshes and and 96 dpi for PCs. Current monitors can display somewhat higher resolution while printing on paper can display as much as 300 dpi. Some examples: to make a high quality 4″X 6″ print you need image that is 300 X 6 (1800 pixels) by 300 X 4 (1200 pixels) which ends up as 2,160,000 pixels or 2.16MP. If you wish to print a 16″X 20″ print, technically, you would need a 4800 X 6000 (28.8MP) file. In reality, with proper post processing, even a 6 – 8 MP camera can produce acceptable results, at least up to 16″X 20″ prints.
To produce the same image on a low resolution computer monitor you need a 72 X 6 (432 pixels) by 72 X 4 (288 pixels) for a total of 124,416 pixels or .12MP.
One last point – The values described above are what are necessary to produce an acceptable quality image. They do not determine the image size, because most modern computer displays allow the user to select the screen resolution. For example, I am typing this on a 17″ (actual width 14.5″) display set at a resolution of 1680 X 1050. Using the screen width in inches and the number of pixels (1600) the resolution of my monitor is about 116 dpi. A 640 dpi image is going to be a little less than 5 1/2″ wide on my monitor. If I change the resolution of my monitor to 1024 X 768, resolution changes to about 71 dpi and the same image becomes a little less than 9″ wide. Without knowing both the screen size & resolution of the monitor your viewer will be using, you cannot determine the actual image size.
If you would like some suggestions as to file size verses print size, check Thom Hogan’s “How Big Can I Print”. The article has additional information that will help you make better prints.
I’ll save how to change resolution for a later posting.