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If you are going to be successful in getting the most out of Photoshop, and thus be able to get the most out of your images, you must have an understanding of resolution. Now for the purposes of this tutorial the term resolution is defined as a description of the amount of image information captured in a scanned image. Now you will see resolution sometimes expressed as DPI, which is technically incorrect. DPI stands for dots per inch and refers to printer resolution, a subject which is outside the scope of this tutorial. The proper expression of a photo scan resolution is PPI or pixels per inch. Now what is a pixel? Well, a pixel is a tiny square of solid color that, when combined with millions of other tiny squares of solid color in millions of color variations, creates a photograph on your screen. Now let us take a look at this group of trees in the fall in Boston that I took about twenty years ago, and we will zoom in on it at sixteen hundred percent RGB. See the tiny squares of color, each one of these tiny squares of color is a solid color, it does not have two shades, it does not have any gradient or any objects, each little square has its own little color. Now the adjacent squares vary a little bit from the one beside it and when you group them all together into billions of little pixels, and you zoom out from it, your image is created. So it should be obvious to you that the greater the number of tiny squares, the tiny variations in shades of color, the greater the detail and the image quality you are going to get. You always want to scan your images at the highest resolution your computer will absorb and this brings us to the subject of hardware. A good high quality scan of a typical slide at four thousand PPI will result in an image size of about forty-five megs, which is kind of hefty. Now if you are scanning prints, you more than likely will not be able to scan a six by four print at a resolution above 600 PPI. The file size that Photoshop will be able to process maxes out at about a hundred and twenty megs, at least on my machines anyway. If you've got a bigger machine than I do, then maybe you can deal with larger file sizes. But above that, generally, Photoshop will choke and crash. Now it is for this reason that more is best when it comes to your hardware, the more RAM the better, the more storage you have on your hard drive the better, the faster your CPU the better. Now it is useless for me to discuss the specific minimum specs on your computer, just get the strongest machine you can afford, and do not skimp on the video card. Now if you are scanning properly, you will have giant file sizes. Just expect it and deal with them and we will talk about the different kinds of scanners in just a bit. Now, as you go about scanning, something else you need to be aware of. You will encounter people at service bureaus and camera shops that will tell you that a scan at three hundred PPI with an eleven by fourteen inch print size is the same as a four thousand PPI slide scan at native slide size. Nothing could be further from the truth. Now let us take a look at these two photos. This is the exact same photograph of my grandson Cody catching his first fish and we are going to zoom in on Cody's shirt, and again, we can see that there are millions of little tiny squares of color that you can see. Now the variations are not very much because we have a tee shirt that is pretty much the same color. But look at the photograph that was scanned at four thousand PPI. The exact same photograph on the exact same scanner, scanned at different resolutions, and look at the difference in the squares. See you have a greater degree of variation from one square to the next, you have lighter lights, you have darker darks, you have reds, you've got some greens, you've got some browns, you've got a greater amount of photographic information in the higher resolution scan, than you do on the lower resolution scan. This one right here was scanned at three hundred PPI, and this one right here was scanned at four thousand PPI. You will always have a better, sharper, clearer, more vibrant image when you scan at the higher resolutions. So no matter what you are scanning, scan it at the highest possible resolution to ensure you capture the most color detail and image information possible. Now we will also follow this rule of thumb even when scanning for the web. Now folks will tell you you only need to scan at seventy-two PPI scan for web images but that too is not my experience. You want to scan for the highest possible image detail and then convert to a three hundred PPI JPEG image, set at whatever size you wish for your online application. Trust me, this is six years of experience talking. If you start with a high quality image, you will finish with a high quality image even when your target finished product is an image on the web. I do not save these web images at seventy-two PPI by the way; I always save my web images at no less than three hundred DPI, even though the web will only display on your screen at seventy two PPI. Burn this into your brain, start with a high quality scan, meaning the highest possible resolution and you end up with a substantially higher quality finished product.