DPI and Resolution
Which dpi is right for me?
Photographs (prints) and Scrapbooks
Slides and Negatives
If you are like many people, you have heard of “pixels”, ”dpi”, “ppi”, or “resolution”. You will hear these terms in regard to devices from digital cameras, to computer monitors, to HDTV’s. With all of these acronyms and media-specific definitions, it can get overwhelming. For our use, think of resolution as the sharpness or clarity of an image.
Pixels, dpi, ppi, and Digital Images
When a digital image is captured it is broken down into small, equally-sized squares or dots called pixels. Each pixel is a tone or color of the sampled area of the picture and collectively these pixels are aligned in an invisible 2-dimensional grid called a Digital Image. The pixel is the smallest basic unit that composes a digital image and encompasses 3 bytes. The number of pixels that are found within a standard unit of measurement – an inch – is what we call dots per inch or dpi (to satisfy you enthusiasts and tech geeks, this is technically incorrect, as "dpi" is a print industry term and the appropriate measure is ppi or pixels per inch).
Lets take a 4" x 6" image as an example. If the image has a resolution of 300dpi, each linear inch of that photograph will be broken down into 300 equally-sized pixels. If your photograph was 4” by 6”, it would be composed of 300 dpi x 6 inches wide = 1,800 total pixels in width. The height would be 300 dpi x 4inches high = 1,200 total pixels in height. If we multiple these together, the 4" x 6" digital image would be composed of 1,800 x 1,200 = 2,160,000 pixels. That is a lot of pixels! But, something interesting happens; when we double the dpi, we quadruple the number of pixels. The same 4” x 6” photograph scanned at a resolution of 600dpi will contain 8,640,000 pixels. That’s a big number, so for simplicity, we like to specify this number in megapixels (one million pixels). So 8,640,000 pixels is expressed as 8.64 megapixels. So far the discussion has been in reference to a “raw” or uncompressed digital photo without discussion of the actual size of the image files themselves. File sizes can grow quite large and so images can be saved in different file formats to reduce the image size.
Introduce the Scanner
Scanners work by "taking a picture" of your photo and converting what it sees to individual pixels. Another way to think of this is to take your photograph and cut the photograph width-wise into 3,600 identical sized strips, then take each of these strips and cut them into another 2,400 uniform squares. You would have a lot of tiny squares. This is what a scanner does electronically within seconds (except it doesn't actually cut or harm your photos!).
All of this boils down to resolution; so why is it important? Because the higher the resolution, the more pixels or pieces of information that are gathered. If the same 4”x6” photograph from above is scanned at 300 dpi and 600 dpi, the difference in visual quality is comparable but will only truly be apparent if you choose to enlarge an image later. So why not offer resolutions higher than what we publish? We do, and our equipment is up to the task (if you are interested we ask that you contact us directly for pricing and available options) but above and beyond our 600 dpi choice you probably would not see much benefit. There are multiple reasons for this. Blemishes, like small scratches or fingerprints, are more pronounced when scanned in a higher resolution and today’s scanning technology is so good that in certain situations, the scanning equipment will pick up the actual film grain – especially in older media. Secondly, file sizes grow exponentially. If there is one message we want you to take from this, it is that resolution is important, and the higher the better - to a point. Let our experience be your guide. Although all of the above explanation used a standard 4” x 6” photograph as an example, the same principles apply to slides and negatives. The difference is that these other types of media are small in size and were initially designed to be enlarged, so we scan these at much higher resolutions using different specialized scanning equipment.
One Notable Exception
DPI is only relevant for print reproduction and does not have any significant bearing on computer displays. Higher resolution generally does mean better quality for print reproduction, but there is one medium that does not require high resolution for standard viewing: general computer and, by extension, internet viewing. For historical reasons rooted with Macintosh computers, 72dpi has been the generally accepted de facto resolution (you can read why and all of the arguments for and against this all over the internet) for computer monitor viewing of images including websites and other applications. There is a lot of bickering about this in the industry that 72 dpi is a myth. Well, for all intents and purposes, it is for computer viewing. As many geeks would like to point out, for example, an image that has 7 dpi, 72 dpi, or 720 dpi will display the same on your monitor and show the same file size. DPI is important for printing, and is simply not relevant for computer display because a monitor has no concept of an inch - it only cares about pixels and the dimensions of pictures given in pixels. Are we contradicting ourselves? No - ScanFlurry uses 72dpi more for tradition than relevance. Most web sites still abide by this dpi value even though its not relevant.. But, take our word for it, 72 offers great quality for online photo albums, digital picture frames, cell phones, computer backgrounds and more. We could offer the photos at 1 dpi and for online viewing it wouldn't matter but it just doesn't matter. Don't believe us? Every single picture on this web site is, of course, 72 dpi!
Why is this important?
At ScanFlurry, in addition to your providing your photos at your desired high-dpi resolution, we are also the only online scanning company to include a complementary duplicate set of your scans at 72 dpi.
ScanFlurry’s Resolution Philosophy & Our Competitors:
Some scanning companies offer photo scanning at 150 dpi, but we don’t believe this is adequate for most applications. Our philosophy is to do once, and do it right! The standard resolution that we offer is 300dpi, although we additionally offer 600dpi for those customers looking for even higher quality. The nominal price difference will provide you more options later for enlargements on good-quality photos.
Disclaimer: The information presented about is for a general fundamental understanding of digital images and will be helpful for just about anyone. Terms used on this page can have different meanings for different applications. Overall quality is not just a function of scanning, but the condition of the original media and the quality of the original picture.