Grayscale images

• File formats: Avoid file formats like PICT, GIF or BMP which were never meant for design purposes.
• Highlight and shadow dots:
  • The clearest point in grayscale images should not consist of pure white but should have at least a 2% dot in it. Acceptable exceptions are headlights of cars or specular highlights (small light reflexions on a shiny surface) for which it is no problem it they are “blown out”.
  • The darkest area of the images also shouldn’t consist of pure black. For 150 or 175 line screens, it is customary to use a 95 percent gray for the shadow dots. For newspaper printing, a 5 percent highlight dot and 80 percent shadow dot is not uncommon.
• QuarkXPress and TIFF: When placing TIFF images in QuarkXPress (Mac or PC) make sure to never have the background colour of the picture box set to “none”. This avoids problems with staircasing (so-called jaggies) at the edges of the image.
• Resolution: Make sure images have the correct size and resolution while scanning them. The final resolution of black and white pictures should be (screenruling x scale x 2). The “2″ is a quality factor that can vary between 1.6 and 2.5 depending on your quality needs and the subject of the image. So if you scan a photograph and want to enlarge it 300 percent in the layout application and your publication is printed at 85 lpi, the image should be scanned at (85 x 3 x 2) or 510 dpi.
• Size: Never enlarge images more than 20 percent in your layout application. It will reduce the resolution of the images and lead to an effect called staircasing. Reducing images too much will lead to a loss in sharpness and contrast.

Colour images

• File format: Avoid PICT, WMF or BMP images. The layout application may support these formats but their proper conversion to PostScript or PDF data is never guaranteed.
• QuarkXPress and TIFF: When placing TIFF images in QuarkXPress (Mac or PC) make sure to never have the background colour of the picture box set to “none”. The image below shows what can happen if the background is set to ‘none’: either there is staircasing (jagged edges) at the edges of the image or white areas within the image simply vanish.

  

• Resolution: Make sure images have the correct size and resolution while scanning them. The final resolution of colour pictures should be (screenruling x scale x 2). The “2″ is a quality factor that can vary between 1.5 and 2.5 depending on your quality needs and the subject of the image. So if you scan a photograph and want to enlarge it 300 percent in the layout application and your publication is printed at 150 lpi, the image should be scanned at (150 x 3 x 2) or 900 dpi.
• Size: Never enlarge or reduce images more than 20 percent in your layout application. Enlarging them will lead to pixelization and staircasing. Reducing them too much will lead to a loss in sharpness and contrast.
• Colorspace: Not all workflows can handle RGB or indexed images properly. Check with your trade shop or printer to see whether they support non-CMYK color modes.

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