Dear, 1. I m very confusing with the Resolutions in Digital imaging. Let's say I take two digital camera to shoot the same view. The 1st 2.1MP(megapixels)digital camera has 1600X1200 res.(10"X 8")while the 2nd 1.3MP d.c.(digital camera) has 1296 X 960 res.(8" x 6").Will I get the same sharpness if I print out both the photo in size 10" X 8" in the same printer? If not, what can i do if I want to get the same sharpness as 10" x 8" by using the 1.3MP d.c.? Is using a higher dpi printer(eg.laser printer) will print sharper & higher quality image on larger sizes(>10" x 8")no matter wat d.c we use....even though with an only 1.3MP d.c. to shoot?

2. Please compare 2.1MP digital camera & 1.3MP d.c. in terms of picture qualities. Can 1.3MP d.c. shoot the same quality as 2.1MP d.c.? Can I increase the print out size if I want to get sharper and bigger image even though I m using only 1.3MP d.c. to shoot? How to do that? (by using different printer? Modify in Photoshop? Or.?)

Thank you for your kindness to answer these questions. I would be very appreciated if you could help me to solve the problems.

Yours truly, Coolsurfy

-- Law Ling Sheau (coolsurfy@yahoo.com), March 18, 2000

Answers

Law, Some good questions. I'll try to answer all of them.

First of all, a 1600X1200 image has an aspect ratio of 1:1.333 (1600/1200=1.333). An 8X10 has a ratio of 1:1.25. You must crop some of the horizontal dimension to get an 8X10. To get an idea of the printed resolution, divide the number of pixels in one dimension by the printed dimension (in inches). That will give you pixels per inch (ppi). The more, the better. For example: 12oo pixels in an 8" print gives 150 ppi. To get the 10" horizontal dimension (at 150 ppi) you need 1500 pixels. You are going to crop 100 pixels off of your 1600 pixel original image.

Now, lets blow up the 1296X960 pixel image to an 8X10" print. Again, the camera's aspect ratio is not quite the same as the print (1:1.35). We will crop the horizontal dimension. 960 pixels printed in 8 inches gives 120 pixels/inch (960/8). 120 ppi, and 10 inches, means we need 1200 pixels out of the 1296 you started with. We crop 96 pixels.

The 1600X1200 image has created an 8X10 print at 150 ppi. The 1296X960 image has printed an 8X10 at 120 ppi. How big a difference is that? Well, not really very much. Assuming that both of these original files are otherwise identical, you may or may not detect a difference. It will greatly depend on the makeup of the image. Pictures of great detail will show a difference quicker than a picture without so much detail. Looking at photos is very subjective. A 120 ppi print will look very good to one person. Another will see that much fine detail is lost. I would suggest that most modern inkjet printers need at least 120 ppi to produce an acceptable image. A couple of hundred ppi will look much better. 300 ppi is about all any inkjet printer can handle. More than that will not be seen. Do not confuse this with the dots per inch that printer manufacturers talk about. This is another matter. A printer capable of 1440 dpi will print many dots (droplets of ink) within a single pixel. Since a printer can only print 4 colors, cyan, magenta, yellow, and black, it takes lots of these tiny drops to actually form a pixel of a different color. (6 color printers add light magenta and light cyan) The pixel is made up of droplets of varying numbers of each of these 4 colors. Highly magnified, you can see these droplets. Under normal viewing, you just see smooth color.

In the above examples, we used no interpolation. We used only the data we had. Programs such as Photoshop can interpolate data to increase the resolution. There are many mathematical formulas that can be used to generate more pixels than what you originaly captured. Some cameras even use interpolation to produce an image with more pixels than the CCD actually captured. In all cases, we are generating false data that may, or may not, accurately represent what was really there. The more data you interpolate, the less accurate the final print will be. There are programs like Genuine Fractals whose sole purpose is to interpolate data to generate larger files. In general, such a program will do better than Photoshop. Especially when you really begin to stretch the files to very large sizes.

I hope this has been helpful. Once you get a grasp of the calculations, I think you will see that resolution is not that hard to understand.

-- Steve (MilwaukeeChrome@aol.com), March 18, 2000.