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DPI and Why - Resolution Does Matter
When I started on the internet I was a photographer and a science fiction fan. Since I had no science fiction photos of my own, I started surfing the web. After several months of looking through many Sci-Fi web sites, I realized that most of those sites used small thumb nail size prints (usually 1 inch x 1 ¼ inch or smaller). This was back in the days that a 28.8 modem was considered high speed.
The reason these thumb nails were so small was that it took so much time for the pictures to come up on the page. When you clicked on an individual thumb nail; a larger version of the picture came up (usually 4x6 or bigger), but it would take a very long time to do so.
Searching all the big images I could find; I saved the ones I liked, and brought them into Photoshop where I could compress them. I made my own site with images that measured a whopping 2 inch x 2 ½ inches, which was better than the small thumb nails I saw every where else. I quickly found that over 90% of their images were saved at 72dpi; so that’s what I did. For several years, I saved all my photos at 2 inch x 2 ½ inches and at 72dpi.
As my interest in photography continued to grow; I realized that a Sci-Fi web site might be cool but it made me no money. I needed to put up a web site of my own photos. By now I was using a 56k modem and decided my pictures needed to be bigger. When I scanned in my pictures I usually did them at 100% at 72dpi; so that all my images on line where now 4x6 in size.
After a few years my lab started offering pictures on CD. They were also 72dpi so I didn’t have to scan them in anymore. Life was good; but they used file sizes like 44 inches x 56 inches which at the time I really couldn’t figure out. I didn’t know anyone who ever printed something that big; so again I took those images and compressed them back down to 4x6 inch size.
Eventually, I started doing the same thing but saving them as 5x7 inch size. My new site (betterphototips.com) looked impressive and actually loaded very quickly. Yes, I also eventually stepped up to real high speed (1.5mbs per sec.) Life was good again; until I went back and started pursuing one of my other great loves (writing). I figured rather than just using this site as a gigantic portfolio; why didn’t I offer something for sale as well. You know the old adage “write about what you know best”? To me it made perfect sense that I should start writing about photography “how to” tips. That’s when things started to get complicated.
When I looking around at self publishing and print on demand publishing, I found that they all wanted pictures to be 300dpi or greater. This was a total shock to me. I had thousands of images ready to use, but they were all saved at 72dpi. I thought that Photoshop could save me again, so I started converting them to 300dpi but something didn’t look right. My 300dpi images looked worse than my 72dpi images. I was at a loss. Then I went back and did my research.
The reason the images on a CD from the lab are so huge (in measurement) is so you can use the images in either format. 72dpi is exactly 25% of 300dpi. If you want your 300dpi images to look as razor sharp as your 72dpi images do on line, the print has to be 75% smaller. In other words, an image that measures 44 inch x 56 inch at 72dpi would be the same quality as an image that measures 11 inch x 14 inch at 300dpi.
If you take an image that was originally 5x7 inches at 72dpi and try to convert it directly to 300dpi, it is not a pretty picture. Similar to the equivalent of the right f-stop and the right shutter speed, you have to take both factors into account! DPI and Size are forever tied together. You can not change one without affecting the other. It is much easier to make something smaller that looks good, than to try to enlarge something after the fact and try to make it look even close to the original. That being said, the best photo tip I can give new beginners today is: ALWAYS save your images larger than you expect to use. Do not waste 15 years of your life and thousands upon thousands of images that can only be used in one way. Always save large!!
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