Print sizes and pixels is the second topic most confusing and misunderstood by novices I have dealt with, after the "just how many mega pixels do I need" question.

Here we need a bit of math and understanding just how well our eyes can see. Print quality on printers are expressed in dot per inch (dpi). This means just how many droplets of ink are placed on the paper per inch. Obviously the finer the droplets are the better the print will look. The higher numbers usually indicate better performance both in laser and ink jet printers. This of course is not quite the case with dye-sublimation continuous printers where it is 300 dpi. But again, we are talking about two different concepts, and not to many dye-sublimation printers are available. Generally speaking, people having normal eye sight can see lines on a print at approximately in the 288-300 dpi range. We cannot tell without magnification by using a loupe or magnifier any differences beyond that. People with visual problems, with poor eye sight, this drops down to the 180 dpi or less range. Therefore, ideally to get an optimum or excellent quality print, we have to print at 300 dpi or close to this number as possible from 288 dpi and up. Anything larger than 300 dpi with our normal eyes we may not be able to detect! While it is nice to have, it is not necessarily a true benefit. However, this has nothing to do with the printers capabilities but the size of the image of the print.

For example, D70 on its highest setting will take an image 3008wx2000h pixels or 6016000 pixels in total or 6.2 MP rounded off. Notice the image size is a 3:2 ratio, which is what a 6x4" print is. The camera records the image at 300 pixel per inch, therefore, 3008/300=10.0267 or 10" for width 2000/300=6.667" high is the maximum image, in other words, 10x6.5/8" is about the optimal print size.

It will still make a very good print at 8x10" if you compare it to the old standard 35mm 8x10" print format! (Note the 35 mm film size is 36x24 mm or 1.5:1 ratio, and the standard 8x10" print size was never a full frame image of the negative but a cropped enlargement, unless you specified you wanted full frame, in which case it was 10" wide by 6.7 " in height, [10/1.5=6.7 or 6.7x1.5=10.05"]. With the D70, that is basically the optimum print size in essence equaling the 35mm 8x10" full frame print out, which of course was not truly an 8x10" in the first place.

If your camera records images at 72, 150 or 180 ppi and then you resize the images to print at 300 dpi with your printer, you will certainly see the differences, in sharpness, and pixel noise (think of snow on your TV screen!). You do not want to print at 72 dpi, 150 dpi or even at 180 dpi. Let me assure you the results will not be pretty in print. On the computer screen with resolution of only 72 dpi, you cannot see much difference accept for the size of the image on the screen! So start thinking of the magic number 300 ppi! Set your camera to record at this if you can adjust, or resize your photos on your computer with Photoshop to 300 ppi for printing!

Confused? Ok look at it from this perspective. Let's say your digital compact camera is a 6.2 MP. It records the image at 3008x2000=6.2 MP. But it records it at only 72 ppi instead of 300 ppi. Ok then your print size at 72 ppi will be 3008/72=41.7" for width x27.8" for height! This is a huge image but you could count the square pixels one by one, it would look horrible. So now with your software, you double the resolution to 144 ppi now your image size is half 20.8"x13.8", but still looks far from acceptable when printed. So you double the resolution to 288 ppi and now the print looks so much better but the size is half the size again or 10.4"x 6.9", However, you lost details in the pixels while you performed this, because they were originally recorded at 72 ppi, and at that size pixels cannot hold as much detail as ones at 300 ppi. So no matter how we twist this, it is math, physics and resolution that our eyes can see! We need 288 minimum (300) ppi + for an optimum print!

So here is a little chart of mine indicating typical camera pixel sizes and optimal picture size limitations. You will notice some interesting facts, but let's define a couple of more important factors; quality of print. As we discovered above, optimal start at 288 dpi or roughly rounded to 300 and poor is below 180 dpi. The points in between are a bit harder to define and it is more subjective but differences do exist. For sure you can see the difference between in the 200 dpi range and the one in the 240 dpi range! Any how for this simple explanation these are my numbers, so you can accept it or make your own conclusions. They do not reflect any post image processing with Photoshop as the print quality can be improved but one has to be quite an expert in Photoshop to do that, and even that has limitations.

From the table above, it can be concluded that having many mega pixels over a certain point do not necessarily improve the printing size by much. There is a sweet spot around 8.2MP but do keep in mind again this truly depends on the physical size (larger is better) and the type of sensor CCD, CMOS, etc. (CMOS usually found in SLR type and not in a compact) and not the resolution size or maximum out put figure of the sensor in pixels. Therefore, while a small point and shoot camera may have the mega pixels in theory, but due to the smaller sensor size and it has to be to keep the costs down and the size of the camera, you will not necessarily be able to print a terrific looking larger print, and may even have some issues with anything beyond 5x7". Remember, just because it looks good on the monitor, it does not mean that your print will look as good! The other thing to remember with the print quality that the "quality" is very subjective.

Personally, I limit my own printing to the above guide 98% of the time. In some rare cases I may make a larger print for example: in a panoramic shot, but then I also spend several hours using Photoshop to prepare the image in order to make it suitable for a larger print. Be very open minded about the hype that you see advertised about mega pixels and print sizes, do not believe that you make a high quality 13x19" print with a point and shoot 8-12 MP compact digital type. Instead start experimenting with different ppi settings and you will see the results with your own eyes and make your own conclusions, just as I did.

There are other factors involved that will influence the image, often over looked are the camera settings: such as ISO settings, and compression of images. If all you can shoot is .jpg that it is compressed, RAW may not be compressed or compressed to a small degree, TIFF is not compressed but on my D2X 12.8 MP camera, a file in TIFF format is 34.9 megabytes in size! That takes time to process!!! Not to mention the type of paper you are using, glossy is the best for high resolution print, printer drivers, etc, all these will affect the quality of the print. So here it is in a mega pixel, I hoped it helped!

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