Print Buying Direct

Although many designers still work manually, most illustrations, photographs and graphics are created and edited using digital tools. Software such as Photoshop or Illustrator, digital capture with a scanner or digital camera, all allow us to create and manipulate graphics digitally. However, there are many ways of publishing graphics so digital images need to be prepared in different ways. The requirements for resolution and overall image quality can differ quite substantially, and images are processed again when plates are made, or when screening is applied to data for output on a digital press. Depending on the image content, operators have to consider what dot shape to use for the screen dots, and whether to use stochastic screening in order to avoid moiré.

Density

For reproduction in a digital workflow, photographic originals, colour negatives and transparencies, have to be digitised using a high end scanner, either drum or flatbed. Desktop flatbed scanners are really only suitable for scanning reflective photos, where the results are not likely to suffer the rigours of subsequent for print. When screening transparencies, it’s important to use a scanner with sufficient resolution to achieve fine detailed and sharp images. Transparencies have a higher density than reflective images.

Digital images

Scanners used to be important for digital image processing, but they are now largely redundant because of the increase use of digital cameras. High-end digital cameras now have enough resolution and image quality to capture images that can be used in a professional prepress workflow. With resolutions of 10MP (mega pixels) or more in the image sensor, even midrange digital cameras produce good enough images for many publishing scenarios. High-end professional’s digital cameras offer even higher image quality, and even surpass what can be achieved when scanning transparencies on a drum scanner. When processing digital photos the challenge is to maintain both shadow details and highlights when processing the raw data from the camera. This ensures that the colour and grey balance are correct and although the camera’s built in software does a decent job for most situations; advanced image processing is often needed to achieve high and consistent image quality. This is especially true for print output. One of the most popular image editing software packages is, of course, Adobe Photoshop, but it takes a long time to learn and master the more advanced functions.

Five major considerations

If every single image has to be analysed and processed manually there are five main areas to consider.

1. decide if the original image has enough resolution for the publishing process to be used, so that all details will appear sharp and correctly rendered.
2. it’s important that the image is rendered with smooth tone transitions, both in the shadow details, in the midtones, and in the highlights.
3. There should be no tendency to banding or loss of fine details.
4. Good overall contrast is key to ensuring that the image has depth, and the colours should be accurate and as bright as possible, rendered with the correct hue.
5. Last but not least; the grey balance needs to be checked. If an image has a colour cast in what should be neutral grey areas (or light and near white areas), the whole image will look strange.

RGB to CMYK

Digital cameras and scanners capture images in RGB, so before converting images into the CMYK colour space for printing, they need to be optimised. On a calibrated monitor a balance in the RGB values, for example a setting of 127 red, 127 green and 127 blue, should produce a mid-grey neutral tone on the monitor, and so in the image.

Compression

Image processing involves many variables. One of the trickiest for many operators is knowing when and how to apply compression: too much compromises image quality, too little means unnecessarily fat files that can slow down production. A popular technology for reducing image file size is JPEG, but although it’s popular, JPEG is actually a lossy compression technology, so JPEG compressed images will always lose some data, and therefore, quality. Advanced digital photographers prefer to use TIFF on their original photos, because it also can compress images but it is not as lossy as JPEG.

For more information on image processing or printing in general please don’t hesitate to contact us at The Printing House (Print Buying Direct)