When modifying and saving your images do you consider the DPI of the image or the pixels or both? What the heck are pixels anyway you ask? Let me try to guide you into a world of understanding as we take an important side trip that doesn’t quite relate to the archival process specifically, but more importantly, how to save them before you archive them so you don’t make the “Big Mistake”. I consider this a very important step in the overall process because you need to know the difference between manipulating and presenting images on screen and printing them in the physical world. Most importantly, you need to understand how DPI and pixels affect the printed photo quality. To completely understand how your images are displayed on your screen and how to print them in the physical world we need to understand three main concepts. The first one is DPI, the second is monitor size and resolution, and the third is the always confusing pixel. Lets look closer…
Dots Per Inch (DPI)
To start off this discussion, lets examine resolution or DPI. (Dots per inch) DPI is a physical measurement used in the print world to describe the amount of printed dots contained within one inch of a printed image. The term is also used by some people to measure the space your dots take up on your computer monitor but that is more acuarately referred to as PPI or pixels per inch. We’ll discuss this further in a bit.
The concept of dots per inch is easy to understand if you look closely at an actual printed image. There you may see very fine dots that actually come together and form that image as you move farther away. In almost all printed material these dots are made up of only four colors Cyan, Magenta, Yellow, and Bladk (CMYK). When you pull back from the image the four colors all visually gel together and form the image that you see on the paper. The mysterious “DPI” concept determines how close those dots are printed per inch of actual paper and how sharp the image appears to your naked eye. For example a newspaper might print their images at something like 170 dpi because it is a lower quality paper and may tend to bleed so it really doesn’t do much good to print at a higher DPI in this case. For your full color glossy magazine photographs though you need a minimum of 300 DPI if possible to attain a decent sharpness and quality level. If you double that to 600 or more you will start to get a really vibrant, sharp image. So when editing and saving your images keep in mind that DPI only controls photo size in the physical world.
Pixels per inch (PPI)
The word pixel is a term that originated from the two words “picture element”. A pixel is the smallest “digital element” visible on your computer screen. If you grasp the concept of DPI in the print world, a pixel is a colored dot that makes up the image or photo that appears on your screen and the size of this dot depends on how you’ve set the resolution of your computer screen. Unlike DPI, pixels are planted firmly in the digital video world. Again, the concept is similar to DPI in that the dots make up the image you are seeing on screen but it has nothing to do with the actual physical world. Let me say that again. Pixels have nothing at all to do with the size of your final printed photograph in the real world.
Monitor PPI, Size & Settings
So the next concept to understand is how images appear on your monitor screen. There are actually three parts to this, PPI (screen resolution or pixels per inch), monitor size and monitor settings. These three elements are not essential to archiving your images but you need to have a basic understanding how they work.
To connect the first concept of DPI mentioned above to this one, the first thing you need to be aware of is that DPI is very similar to PPI but at the same time they are completely different. DPI measures the physical, real world dots that appear on paper, PPI measures the dots of color per inch on your computer screen. As in the print world, the images on your screen are made up of these dots (pixels) and most newer monitors show 96 pixels per inch on screen but you may have a slightly older model that shows 72. It’s a safe bet though that your screen will show either 72-96 pixels per inch on the actual physical screen space. Please consult your manual to be sure. It’s very important to understand that DPI and PPI are not the same thing and they do not relate to each other even though they are similar concepts. They are two separate settings uses for two different solutions.
Now that I’ve drilled that into your grey matter, the next item to be aware of is monitor size — video and computer monitor sizes are measured from the top corner and then diagonally to the bottom corner at the opposite side of the screen. So if you purchase a 17 inch monitor the actual width of your monitor would be about 13 inches horizontally. This would then give you about 800×600 pixels of actual viewable area once you take into account the space lost around the edges, etc.
Why do they do this you ask? Well your first guess is probably right. When TVs were first introduced into the marketplace manufacturers wanted to make their products sound more impressive than they actually were and the measurement process stuck. Be sure when purchasing a monitor or television that you ask what the viewable screen size is to get a more accurate description of the screen size. Your monitor settings can also be adjusted depending on your hardware and memory and we’ll discuss that futher below.
Another part of the puzzle is your monitor settings. In your system control panels you will notice an option to change the settings of the monitor resolution. An example would be 800×600 or 1024×768 and they stand for the total pixels horizontally and vertically. This setting can be controlled based on your personal preferences and will make elements on your screen appear relatively larger or smaller depending on the setting because you are essentially increasing or decreasing the PPI or pixels per inch that appear on your screen. So to quickly illustrate what I mean by using the previous example, if you have a 15 inch monitor it might only have a maximum PPI of 800×600 but a 21 inch monitor maybe set to 1024×768 or even 1280×854 thereby making that same image sharper because you have more PPI. (Similar to the concept of the 300dpi vs. 600 dpi image described previously) The easiest way to understand this concept is to consider a window screen. If you place your eyes close to the screen you clearly see that there are holes in the screen, but if you place the screen across the room it appears as a solid grey or even totally tranparent depending on the lighting. This is because the holes are very small and your eye starts to treat them as one solid color or nonexistent at a distance.
Bringing it all together
My main point that I am trying to make here by going through all this technical mumbo jumbo is that monitors do not show exactly what you get when you make a print of your final image. The quality of your print depends on real world measurements like DPI, not PPI. To completely understand how a monitor works it might be worth researching on your own and I could go into several examples to illustrate these points but to keep it short and sweet there are just two important concepts to keep in mind when saving photography, just remember that DPI controls how large an image prints in the physical world and pixels control how large your image appears on screen in the digial world. So if you plan on presenting your images on screen pay attention to the pixel width and height of your image, not the dpi. If you plan on making prints of your images make sure to save your images at the highest DPI possible. This is the main concept to understand.
Viewing your images on screen
When archiving your images I believe there is a place for saving lower resolution images. You may want to post the images to a web site or share them via email with family and friends. You may also want to keep a copy for quick reference since original files can be large and time consuming to open. (This is the core cause of “The Big Mistake” by the way) There are many programs and methods for archiving and quickly viewing images (which we will discuss in later posts) but one of the most simple is to just open images by dragging them to an open browser window from a folder on your hard drive. You could never do this with a high-res image and it makes for a nice down and dirty solution for viewing your your images quickly.
One other additional item to note when manipulating your images on screen is that there’s actually a common rumor that images that appear on your screen need to be scanned and saved at 72 dpi. I’m sure you will agree that this is not true if you paid attention to the explaination above. If your image is only going to be used on a computer screen you can set your DPI to 5 DPI or 5000 DPI if you like and your image will appear exactly the same size on screen with no degradation of quality because the screen only shows pixels. Let me clarify this like I did above and repeat it. DPI has nothing to do with image size on the screen. Now, if you printed out those same images in the physical world you would get dramatically different results since one image would have 5 dots per inch and the other would have 5000. Don’t believe me? A great site to reference regarding this theory is at this address. This gentleman puts the argument to rest quite nicely. This brings me to the second most important issue when saving your images, the physical prints.
Making prints of your images
The second process that we need to understand here is the concept of making prints of your images on physical paper. I’m sure most of us plan to do this so DPI and actual image size (inches) is everything when saving your images, the more DPI your image has, the better. Always save your digital images at their maximum size just in case you decide to make large prints in the future. A good rule to follow in preventing you from making the “Big Mistake” is to manipulate the original image and save it as a separate file each time you change the size, color, etc. So if you ever decide to change that image again or print it larger you can always refer to the original file. Simply stated, if you print out your images as 4×6 prints at 300 dpi and one day you decide that you want to print out that same image at 8×10 you won’t be able to do it without a serious loss in quality and a very large disappointment.
I have seen so many people that have even manipulated all their original photos down to small JPEG files on their personal web site and never thought to save the original file! This is my main reason for including this chapter so you understand when you make the decision to save your images as JPEG files and post that image at 450 pixels wide on your web site, you will never again be able to make nice physical prints from them unless you saved the original file as a backup. Sorry to break the bad news if you fall into this category but hopefully those of you who are reading this before you make the “Big Mistake” now have a better understanding of the digital world vs. the printed world.
To sum up everything I have just said there are really only three main points that you need to understand. First, DPI (Dots per inch) is for printing your images. Pixels are for viewing your images on screen and always, always, always remember to save your original files. You may seriously regret it down the road if you convert all your original files to small JPEGs to save space and then later decide that you want to make prints. It just can’t be done with any high degree of quality and in the digital world you have no backup baby! I would consider the understanding of these concepts as an essential first step to successfully archiving your beloved photography.
Your final images – Further study.
Once you understand the basics of viewing and saving your images spend some time working with popular image editing programs like Adobe Photoshop. Read books on image manipulation, color correction, photo retouching, scanning, etc. There are endless resources in print and online that will help you improve your images. The discussion of these subjects are actually beyond the scope of this series but they are a very important part of digital photography. Educate yourself because they are all equally important subjects that deserve your attention and ones that will make your photographic work even better!
Now that we have that out of the way and we all know what the “big mistake” is, it’s time for the “big decision”…. What type of media will I choose to archive my photos! Back soon with part 7…
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