Soft proof
A soft proof (roughly: Soft test print, in analogy to software ) is a binding digital proofing on a monitor or projector under defined lighting and environment conditions, before a final order is released to a printing can be done. The colorimetric and content correctness of digital print data can be checked here.
The same conditions apply here as for the binding test print in paper form. The software used must enable the calibration and profiling of the output device, i.e. a monitor or projector, it must guarantee validation for the print standard of the subsequent production and enable the output of the print data. Only the actual print data, ideally in PDF format, may be used.
Explanation
In a narrower sense, soft proof is the simulation of a specific output condition - usually a printing condition - on a monitor. An output condition is characterized by the target values to be achieved, which are influenced by the combination of the materials, devices and their control. Typical output conditions are e.g. B. offset printing according to “Process Standard Offset Printing”, printing with an inkjet printer on a specific paper or exposure of photo paper in a minilab.
The file used for the soft proof can be an image file in a device-dependent (RGB, CMYK, multi-channel / special colors) or device-independent (CIELAB, CIEXYZ) color space . The file format are e.g. Commonly used, for example, JPEG or TIFF . Device-independent information (mostly in the form of an ICC source profile) must be available for the correct color display of device-dependent data .
The file can also contain image elements, graphic elements and text in different color spaces in a container format (usually PDF). For an “open” file in a layout program, a soft proof display can also be desired. Files in 1-bit format that have already been broken down into individual color separations (e.g. CMYK) for the exposure of a printing plate can also be used for the soft proof.
In a somewhat broader definition, soft proof is generally understood to mean the color-correct display of an (image) file on a monitor. A typical application occurs with photographers who assess the color of an interpreted RAW file on the monitor or who use the data in an RGB working color space directly, i.e. H. without pressure simulation, display on the monitor. Many common graphics programs offer the possibility of a print simulation, such as E.g .: Photoshop, InDesign, CorelDraw, whereby the ecological benefit and the time savings as a result of hard proofs (simulation of the later printing on print medium) speak for the use of a soft proof.
The following points are important prerequisites for using the softproof function:
- Softproof-capable program
- Neutral environmental conditions
- Familiarity with the ICC profiles of image files and printers
- Display of the printing color space on the monitor
- Calibrated screen
In the sense of this definition, a so-called “static proof”, in which the display of a layout is checked on a monitor, is not a soft proof. Here the correct color representation is only given a subordinate role; Checking the file on the monitor is primarily intended to ensure the correctness of the content and status, which is reproduced on the basis of the print data after processing by the RIP. In order to clearly distinguish it from the color-correct representation of data, the term "softproof" should not be used here, but a term such as "standproof" should be selected.
Current situation
At the moment (as of March 2012), two main scenarios are decisive for the soft proof: On the one hand, the coordination, for example, between an advertising agency and the customer who should view the same color result on two monitors at two different locations at the same time. On the other hand, the color matching on the printing machine with the actually printed result. A soft proof is particularly desirable here for cost reasons: If color matching can be carried out with a monitor image instead of an expensive “contract proof” on paper, there are no additional costs apart from the purchase of the monitor and, if necessary, soft proof software.
However, it is precisely in this most important scenario that the strongest limitations of the soft proof become apparent. While in printed halftone proofs the representation of the halftone of the print and the offset rosette can be checked, the monitor softproof is always unscreened. The lighting at the printing press control station is still a problem today: While the control station has to control the printing and color matching according to the ISO standard 2000 lux ± 500 lux brightness, the current softproof monitors only generate a fraction of the brightness. This was solved, for example, by installing a light booth next to the control room, in which a monitor and a darkened light source with standard light were installed. The printer controls the printing on the machine in bright 2000 lux light and then places the printed result in the dimmed and shielded light box in order to match the color with the soft proof on the monitor. In practice, however, this turned out to be quite difficult, as the print product had to be compared under different brightnesses. The dimmable standard light at the control center with softproof monitor is therefore a further development: Here, the sampling takes place at the same place, only the lighting of the control center has to be dimmed for the color matching with the softproof.
In the meantime, matching monitors are also available that have up to 700 candelas per square meter of luminance and thus theoretically manage without dimming at the control desk. In reality, current softproof monitors can now provide a luminance of up to 200 cd / m² for more than two years , so that the lighting in the control center has to be reduced to just 700 lux, roughly a third. That is still a difference, but it is already used in production today. In addition, there has recently been a proof monitor that is advertised with a luminance of 700 cd / m² and can actually be operated with a luminance of 450 cd / m². The lighting of the control center therefore only has to be reduced by around 500 lux, which could be mapped within the ISO standard (2000 lux ± 500 lux). This would create the prerequisite for using a soft proof on a monitor directly on the printing machine without dimming for color matching. However, this monitor can only display approx. 90% of the color gamut of the most common ISOcoatedV2 / FOGRA39 printing conditions. In newspaper printing, however, ISO-compliant production conditions with the advantages of soft proofs are already possible.