DIGITAL IMAGES
When using raster (bitmap) images such as photos, it is important to ensure the images are of sufficient quality for printing on a press. Please follow these guidelines for all raster images.
Back To File PreparationIMAGE RESOLUTION:
Use only high-resolution images. Resolution is measured in dpi (dots per inch) or ppi (points per inch). Images must be 300 dpi or greater at actual size.
To create images at the best quality possible, make sure:
- Images are scanned to the intended final size at 300 dpi or greater. The higher the dpi value, the larger the file. However, a higher dpi value may not result in better quality. If the resolution is set too high, the image can become muddy once printed.
- Set your digital camera settings to the highest quality possible. Digital cameras with 2.4 megapixels or less may not be able to produce quality images large enough for your project.
- If using downloaded stock images, verify that the image is the appropriate resolution and size for printing. Do not use Web media stock images.
- Do not convert, or interpolate, low-resolution images to high-resolution. This is often done in Photoshop by using "Image Size" and checking the "Resample Image" option at the bottom. If the image is 72 dpi, or other resolution setting less than 300 dpi, the only way to properly convert to 300 dpi is to deselect the "Resample Image" option and change the resolution to 300 dpi. This will make the "Document Size", and the optimal print size, smaller and preserve the original "Pixel Dimensions" of the image without interpolating the image. The key to remember is that you cannot make an image any higher-resolution than the original.
- Do not use images taken from screen captures or stolen from the internet. To find appropriate high-quality images for your projects, look for stock art suppliers such as:
- Even images that appear crisp on the screen may not work well; almost all images you see on the internet are 72 dpi, highly compressed and inadequate for press.
The resulting print quality from an image intended for the internet and a print-ready file.
- Do not "scale" the image more than 125% or less than 75% in page layout programs. This is the same as interpolating your image. Ideally, images should never be scaled within a layout program.
COLOR MODES:
CMYK COLOR:
The image color mode is just as important as its resolution. For optimal print results, only CMYK or grayscale images should be used throughout the artwork. CMYK is also known as 4-color Process. CMYK images are composed of Cyan, Magenta, Yellow and Black separations which combine to create a single color image. A grayscale image has only one component: a black composite.
The right image illustrates the the CMYK separations of a file.
PANTONE and RGB COLOR:
Pantone colors are considered "spot color" and not CMYK Process. Please convert all Pantone colors in your design or layout to its CMYK process color equivalent. For the most accurate conversions, Pantone offers conversion guides for spot color to process.
RGB images are more appropriate for websites and are not recommended for use in print projects. All RGB files, such as scans and images from digital cameras, and any spot, or pantone colors must be converted to CMYK. Indexed Color, or Duotone files should never be submitted for standard printing.
COLOR SHIFTS
Although an RGB file, or even spot color files, may print beautifully on an office or home inkjet or laser printer, drastic color shifts and other problems can occur when printing in full color process. The images below indicate some examples of color shifts.
The image on the left is a CMYK TIFF image. The right image is a CMYK JPG file.
Note the washed-out appearance resulting from the JPG file.
The image on the left is an RGB TIFF image. The right image is a RGB JPG file.
Note the red color-cast on the first image and the washed-out appearance of the second.