Use of images

Image resolution

Ensure that the image resolution is sufficient for printing. Ideally the image resolution is twice the screen line. The screen line ruling is determined according to the used paper and press.

Guideline values for image resolution:

Preparing the images with resolution 350 ppi, you ensure the resolution is sufficient for all printing. If you know which paper will be used, you can surely prepare the images to a lower resolution. As a benefit you’ll get a smaller file size, otherwise it has no importance.

Total Ink Coverage in CMYK images

The total sum, in percentage, of partial colours in the darker areas of an image are determined according to the paper and press used. In addition, this value is also affected by any UCR or GCR function that is used. Today, the ICC profiles include this information. By using a proper profile in colour separtaion a correct TIC (Total Ink Coverage) value is determined automatically into the images.

The total ink values used for standard output profiles are described in the table below. The total ink values in the table – and the functionality of the profiles – are based on the printing according the values defined in standard.

Guideline values for Total Ink Coverage (TIC):

Dot gain

Dot gain is determined in images according to the print method, paper and the colours used. Grafostil follows the dot gain values defined in ISO 12647-2 standard. The dot gain increases gradually when going from hevy coated paper to uncoated paper. Also, dot gain values are included in an ICC profile. For this reason, it is important to know at the image production stage for which process and on what kind of paper the job will be printed, and then use a proper output profile for the CMYK conversion.

Enlargement of images in publications

If the image resolution is in accordance with the guideline values, you can safely scale the image in publications from 75% to 125% of original size. The greater the change in image enlargement, the poorer the quality of the printed image. If you intend to reduce the size of the image to less than 75% of original size, make the change in the image processing program.