Megapixels

For sales reasons manufacturers do not clearly explain the relationship between megapixels and dpi on lower end 35mm negative scanners. The use of the pixel itself as a unit of measure is not consistent with higher end scanners. Remember that printers, scanners, and monitors all can be set to various size dots or pixels. The pixel is the smallest addressable screen element, it is the smallest unit of picture which can be controlled. It is the same as the dot. One of the greatest features in modern printing is the ability to vary the dot or pixel size.



Using the popular 5 megapixel size of many low end scanners yields an image of about 8.5 by 6.5 inches from a 35mm negative when printed at 300dpi. This is its "natural size", the size the image will be if left unaltered and printed at 300dpi. This 5 megapixel rating is its hardware capability. The value is calculated by multiplying the width by the height of the resulting image. DPI is calculated, as the term implies, in dots per inch. The fact that the inch is not variable produces a standard. No software or other manipulation can change this hardware value due to it being a physical attribute of the hardware itself. Some scanners allow one to set the software resolution as high as 3600dpi causing the machine to do the same scan with software setting to a higher resolution. This gives a higher resolution at the image but not higher "quality" – nothing about the hardware has changed. This ability to apply software after hardware can be good if manipulation is intended. To scan any negative with enough quality to blow up and not down, today’s scanners need to start at about 1800 to 2400 dpi!



Much of today’s amateur work is web related making the small scanners a real bargain. Having a more versitile, higher quality scanner allows the user more options, as not all imagery is web bound. As stated, software can output any size file from the same hardware source but Quality is a function of hardware first. This is the first stop for your negatives.



Lets look at the popular 5 megapixel measurement. To convert that to comparable dpi one merely takes the square root of its megapixel rating. That gives a dpi of about 2200 for the 5 megapixel size. That’s the actual resolution of a 5 megapixel scan. A 3000dpi scan is 9 megapixels. A 4000 dpi scan is 16 megapixels.



Quality is determined by multiple factors starting with the hardware and ending with the consumer. These mathmatics are here to assist you in making your decision – to ferret out the manufacturer’s hype.