Scanning Images for Web Use

Take the mystery out of getting your images on the Web. This tutorial will teach you the basic information you’ll need to scan graphics for Internet usage.

As humans, we live in a dominantly visual world. Since pre-historic times man has communicated via visual representation. We’ve been refining and changing the way we do it ever since. Two of the latest innovations used to further this age-old quest are the scanner and the Internet. Getting scanned images onto your Web page isn’t difficult. These guidelines will assist you in getting clean, professional looking results every time.

Materials:

  • Computer
  • Scanner
  • Image editing program
  • Scannable art work
Difficulty: Novice
You need to be familiar with your equipment and software. Have the manuals handy if possible. You may need to consult them.{mospagebreak title=Monitor Calibration} The first part of the battle is not the most obvious. How does your monitor look? No, not the smudges and other gunk (although it’s a good idea to remove these now). If you haven’t calibrated your monitor, I recommend you do. Version 5.0 of Photoshop comes with software to help you calibrate your monitor. There are also many 3rd party solutions available. If you own a Mac compatible you can use Colorsync from Apple for color management and gamma correction. If you’re on a Windows compatible PC then your video card might have calibration software with it. Try for a target gamma of about 2.0. (Gamma refers to the difference between the input to a monitor versus its output. It’s in between the standard PC gamma of 2.2 and the Macintosh default gamma of 1.8. You can choose whatever settings suit you, but keep in mind that your audience probably isn’t using your monitor. The more neutral your monitor is, the better possibility you have of creating an image that looks good on other monitors too.

Does your scanner’s software offer automatic color and contrast compensation? Try it out and turn a critical eye to the results. Is it obviously out of whack with the piece you scanned? If so, consult the manual on how to set the curves for your scanner. It’s much easier to get a good scan the first time then to try to fix a bad one later. Most scanners, even inexpensive ones, do a passable job in digitizing images these days. Don’t be misled by that statement. A good entry-level DTP scanner can cost several thousand dollars and a high quality drum scanner will cost $10,000 or more. Most low-end flat bed scanners are suitable for basic scanning needs such as on screen graphics.{mospagebreak title=Getting the Best Image} Photographs are a common item to find on your scanner. If the image is fairly clean and needs little adjustment, scan the image at millions of colors at 72 dpi. This is the straightest path to getting an image on the Web. Save the file as a JPEG at image quality 3 or medium. Done!

Are you scanning images from a brochure or catalog? Color printing usually consists of dots of different colors placed closely to each other to give the illusion of continuous color. If you have a magazine or other printed piece handy look closely at the images. You may not see these dots at first glance. In fact, you’re not supposed to. The whole point is to create the illusion of continuous tone. Even if you don’t see these dots, you’re scanner will. The resulting patterns are called moiré patterns. Most scanner software has a “de-screening” function available. If yours does, select the setting that most closely matches the type of print you are scanning. If you’re scanning newsprint, select newsprint. If scanning a magazine, select magazine, and so on. By using the de-screening function you may get a perfectly usable image at 72 dpi. If after using the de-screening filter you still have unwanted moiré artifacts or if you don’t have a de-screening function try using these suggestions.

Even though you’re only going to need a 72-dpi image, you may find it necessary to scan the original at a higher resolution and then down sample it to get acceptable results. Choose a resolution that isn’t a multiple of the line frequency of the printed material you are scanning. Not sure what the lpi is for the piece you’re scanning? Here is some number to give you an approximate idea; these numbers are by no means exact.

News Print – 65 lpi
Magazine – 133 lpi
Art Magazine (fine prints) – 175 lpi

I usually use 147-dpi. It’s a fairly odd number (in context) and will usually help to break up any unwanted patterns. Be sure to still use the de screening filter on your scanner even if you employ this over sampling technique (assuming that you have the de screening filter). If the result is satisfactory, or very close, down sample the image to 72-dpi and save it out as a JPEG.

Still not useable? Try blowing the darned thing up! Not with explosives, enlarge the image in your image-editing program. 300% should do the trick. Then resize the image back down to 72-dpi. Making the image larger forces the program to “fake” the additional pixels leaving the image slightly blurry. When you resample the image back to 72-dpi, the program has to throw away a lot of the pixels making it “average out” the results. You can also use odd multiples when resizing an image to further reduce unwanted artifacts. Resizing an image this way “jumbles” pixels together minimizing artifacts.

Another trick you can try is rotating the image a few degrees. Sometimes this just isn’t acceptable, but if so, it can help you break up visible and unwanted patterns in your image. Of course, you can employ any or all of the above techniques. Just keep in mind that all of these are “destructive” actions (except for scanning, of course.) A destructive action is one that destroys original pixels and replaces them with pixels of a different value. For example, cropping an image isn’t a destructive action but resizing it is. Cropping an image doesn’t change the pixels that are left; it removes those that are no longer wanted. If you resize an image, you change every pixel left in the image to a different value.{mospagebreak title=Tips & Tricks}

  • Always save images for use on the Internet at 72-dpi. The only exceptions to that rule are so few I won’t cover them. I don’t have many “hard and fast” rules, but this is one of my biggest. Anything more than 72-dpi causes files to be larger than needed and increase download times.

  • Don’t resize an image using the size tags in your HTML. Make the file the proper size in your image-editing program. Do your cropping, stretching, shrinking, and other resizing tasks BEFORE you save the file out. The only situations I can see cause to resize an image via HTML tags is in the case of a single pixel GIF or for odd special effects. Don’t do it for everyday run-of-the-mill image resizing.

  • Don’t use files intended for a Web site for print. Files destined for print need much higher resolution than files to be displayed on screen only, at least by twice the number.

  • Do you have rights to reproduce the image you’re scanning? Copyright law is REAL and can carry some very stiff penalties if disregarded. Only use images you have legal rights to use.

  • Don’t blur an image to get rid of an annoying moiré pattern. By the time you’ve eliminated the moiré, you will have eliminated a lot of your image too. Try the above listed tips and keep in mind sometimes an image can’t be salvaged. If you absolutely have to use this specific image “No Matter What” then consult your local imaging expert. They may fix something that you can’t. After all, there are some reasons why graphic artists and such are occasionally employable.

  • Scan everything at the highest number of colors possible unless the item is grayscale or line-art. Even then, it’s often a good idea to reduce the number of colors after you’ve scanned the image. You can always get rid of information from an image to make it smaller, but it’s nearly impossibly to “add back” what was never there.

  • Is the image you scanned sharply defined line based artwork such as a logo? As a general rule photographs and images with smooth, subtle transitions should be saved as JPEGs. Sharply defined line-based art should be GIFs. Every image is different, so experiment. The right file type can make an image, or destroy it.

Getting usable scans onto your Web site isn’t hard. Follow these guidelines and spend some time getting to know your equipment. Working together, with proper application of these ideas, we may save millions from the sheer horror of unsightly scanned images on the Web. Okay, maybe that is a little lofty. This probably can help your site look nicer and load a lot faster, and wouldn’t that make the world a nicer place?

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