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PhotoShop is one of the most demanding programs you can run on your computer and knowing how to tweak and tune your machine and your software can help to eke out extra horsepower.

  Knowing the 'how' to get the best-colour and the highest-quality images out of your system in the fewest steps can save you hours of messing about.

  How much RAM? There is a saying in the pre-press world: 'Only God has enough RAM.' That is not quite true, but the important point here is that RAM can do a lot more for the speed of your system than a more powerful processor.

  When you open an image in PhotoShop, the software will need to keep several copies of the image, and it will need to have some RAM left over for the purpose of manipulating the image.

  In other words, the amount of memory needed by PhotoShop is far greater than the file size of the image that you are working with.

   How much greater? As much as 51/2 times, depending on what you are doing with the image.

  Some simple processes only need three times the file size.

   To get the best possible performance out of your computer, it needs enough RAM to run the operating system, plus any other software you might need to run along with PhotoShop, plus an amount of RAM equal to five times the largest file size that you normally work with, plus an extra meg or two for the printer, networking software, and so forth.

   In the pre-press world, this can mean real headaches, as file sizes are very often 60 MB or more. This means 300 MB of RAM, plus an extra 10 or 20 for the system and the printer driver.

  If you don't have that kind of RAM, PhotoShop will still run. It uses its own virtual memory scheme. The extra copies of the image are stored in scratch files on your hard disk.

  The more you use the hard disk to keep scratch files, the slower your system will run. In real-world terms, this means that a top-of-the-line computer with only 32 MB of RAM can still open and work with a 60 MB file (provided you have enough space on your hard disk for the scratch files), but the computer will run much more slowly than a system with a much cheaper processor and 320 MB of RAM.

   Some software can help you enhance the performance of your system. Norton Utilities not only can help keep the gremlins from eating your hard disk, but by running the Speed Disk component of Norton, you can optimise the free space on your hard disk.

  If you are running a Mac, turn the disk cache size all the way down. PhotoShop has its own disk cache scheme and Apple's will only get in the way. You can also use the extensions manager to turn off extensions that you don't need, which will free up extra RAM.

   Also, you can remove any unwanted keyboards and the System Suitcase. Removing all of them will give you an extra meg or more of RAM.

  Many commands in PhotoShop have command key shortcuts, such as command m to access the curves. By learning these shortcuts, you can save yourself a huge amount of time.

  All of the tools have key shortcuts: w will switch to the magic wand, l to the lasso and c to the crop tool. All of the tools' shortcuts are listed on the quick reference card that comes with PhotoShop.

   Frequently used menu items can be assigned to a function key. If you have PhotoShop 4, you can assign more elaborate tasks to the function keys by using Actions.

  Most scanners use a colour bit depth greater than the 24-bit colour used by PhotoShop. This means that the colour fidelity of the software used by your scanner can be quite a bit better than PhotoShop's.

  By doing most of your colour correcting in the scanner's interface, you can achieve better results in your final image. Some scanners, such as the Agfa Duoscan, will actually allow you to make a high-bit acquire.

   The image imported into PhotoShop will be 48 bit rather than 24, and, by correcting colour while still in the 48-bit mode, you can achieve results that are superior to a straight scan.

  The key to getting a good image from a digital file involves keeping the posterisation of the image to a minimum. Posterisation will result in a loss of shadow and highlight details as well as poor colour.

  The most powerful colour correction tool in PhotoShop is the curves command. The curves command gives you absolute control over which tones are changed and how, and will correct the colour in a way that causes the least amount of damage to the image.

   The curves box shows a graph that represents the tones in your image with the mid-tones in the centre, the highlights at one end and the shadows at the other. By grabbing the line at the centre of the graph and moving it up or down, the mid-tones are lightened or darkened.

  By grabbing the end points, the highlights or shadows can be altered. At the top is a pull-down menu that switches between the red, green and blue colour channels and RGB, which affects the overall lightness and darkness of the image.

  By using the red channel, the image can be made more red or cyan in the highlights, mid-tones or shadows. The green channel affects green/ magenta and the blue channel blue and yellow.

   Once you have mastered the curves window, it will be almost the only window you need to correct colour in an image. The most important window to avoid is the brightness/contrast control. This function is fine for graphics, but it will destroy photos by compressing the tonal range of the image.

  Selective colour is one of the slickest functions in PhotoShop. No matter how good your camera, film or scanner, there is always a picture that looks fine, but the red in a baseball cap or the green of the grass is just not quite how you remember it.

   Curves are good for making overall colour changes, but trying to enhance the colour of one object in an image can have an adverse effect on the colours in the rest of the image. Selective colour allows you to work with just the reds or greens or neutrals of an image.

    The last in my list of favourite colour correction tools in PhotoShop is the hue/saturation window. By using the saturation slider in this window, you can make colours pop and bring a bit of snap back to an image. It will also allow you to increase the saturation of one particular colour, very much like the selective colour control.

   If an image lacks sharpness, there are two things you can do to try to correct the problem.

   Increasing the contrast of the image will make it appear sharper. To do this in the curves window, simply grab the end point on the bottom left and pull it a bit right, and grab the top right-end point and pull it a bit left.

  Secondly, you can use the unsharp mask filter. It is best not to use the sharpen, or sharpen more, filters as they tend to add a lot of grain.

  Digital cameras have their own unique problems. Images can often have strange colour cast and shifts you do not normally see with images scanned from photographic materials. The two most useful tools here are the hue/saturation window and LAB colour. You can try correcting colour shifts by changing the hue in the hue/ saturation window.

  By changing the colour mode from RGB to LAB, it is possible to correct some other problems that tend to be unique to digital stills. LAB colour has three channels, the first representing the details of the image and the second two representing the colour content only.

  You can see these channels by pressing command 1, 2, and 3 in PhotoShop. Command 0 will show you a normal image again in PhotoShop 3 and command ' does the same in PhotoShop 4.

  If you apply a heavy dust-and-scratches filter to the second or, more importantly, the third, channel you can remove some of the noise that digital cameras are prone to without blurring the details in the image.

  There are several good books that explain techniques and strategies used in PhotoShop. Professional PhotoShop and World PhotoShop 3 are two good choices. Chris Walton can be contaced via e-mail at waltoncr 



Fine-tuning latest PhotoShop