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By Root 1888 0

that you can always guarantee being able to meet clients' constantly changing demands, even though the actual resolution required to illustrate a glossy magazine double-page full-bleed spread is probably only around 40–60 MB RGB or 55–80 MB CMYK. Some advertising posters may even require smaller files than this, because the print screen on a billboard poster is that much coarser. When you are trying to calculate the optimum resolution you cannot rely on being fully provided with the right advice from every printer. Sometimes it will be necessary to anticipate the required resolution by referring to the table in Figure 5.8. This shows some sample file size guides for different types of print jobs.

Figure 5.8 Here is a rough guide to the sort of megabyte file sizes (for flattened 8-bit TIFFs) required to reproduce either a mono or CMYK file for printed use. The table contains file size information for output at multiples of ×1.5 the screen ruling and ×2 the screen ruling.

Bicubic Smoother

This is the ideal choice when making pictures bigger, as it will result in smoother, interpolated enlargements. It has been suggested that you can also get good results using Bicubic Sharper when interpolating up before going directly to print. However, this ignores the fact that print sharpening should really be applied as a separate step after interpolating the image and the sharpening should ideally be tailored to the final output size (see Chapter 13). It is therefore always better to use Bicubic Smoother followed by a separate print sharpening step. This is because the smooth interpolation prevents any artifacts in the image from being overemphasized and the sharpening can be applied at the correct amount for whatever size of print you are making.

Bicubic Sharper

This method should be used whenever you need to reduce an image in size more accurately. If you use Bicubic Sharper to dramatically reduce a master image in size, this can help avoid the stair-step aliasing that could sometimes occur when using the other interpolation methods.

Step interpolation

Some people might be familiar with the step interpolation technique, where you can gradually increase or decrease the image size by small percentages. This is not really necessary now because you can use Bicubic Sharper or Bicubic Smoother to increase or decrease an image size in a single step. Some people argue that for really extreme image size changes they still prefer to use the 10% step interpolation method.

Basic pixel editing

In Chapter 3 we explored the use of adjustments and other tools in Camera Raw to optimize a photo before it is opened in Photoshop as a rendered pixel image. The following section is all about the main image adjustment controls in Photoshop and how you can use these to fine-tune your images, or use them as an alternative to working in Camera Raw, such as when editing camera-shot JPEGs or scanned TIFFs. The techniques discussed here should be regarded as essential foundation skills for Photoshop image editing, because however you bring your images into Photoshop, you will at some point need to know how to work with the basic image editing tools such as Levels and Curves.

Raw to pixel image conversions

Once a raw image has been rendered as a pixel image you cannot revert to the raw data version because the raw to pixel image conversion is a one-way process. Once you have done this, the only way you can undo something in the raw processing is to revert to the original raw image and generate a new pixel image copy. Although the goal of this book is to show you how to work as non-destructively as possible, this is the one step in the process where there is no going back, and you therefore need to be sure that the photograph you start editing in Photoshop is as fully optimized as possible. In the case of JPEG images, you can edit these in Camera Raw if you like, or use Photoshop to carry out the image optimization.

If you intend bringing your images in via Camera Raw, it can be argued that Photoshop image adjustments are unnecessary,