A proof is suitable for two types of color control: firstly, during the creation or retouching phase, e.g. to reconcile a color retouched image with the original, and secondly to check the final data directly before printing.
For control proofs during the data creation of a project, the data format usually does not matter. Whether PDF, JPEG, TIFF; EPS, PS or even PSD… Many proofing companies accept a variety of data formats. For a correct evaluation of the result, however, it is important to proof in the color space in which the print product is also created later. Data for a letterhead should therefore be proofed in ISOUncoated or PSOUncoated, while products printed on image printing paper should be proofed in ISOCoatedV2. For yellowish paper, newsprint or gravure printing, there are many other profiles for which a proof can be produced. You can find a good overview of the current proof profiles here. It is also important that the proof format and the final print format do not differ too much. Only in this way is a correct check possible.
When the brochure has been laid out or the catalogue production has been completed, a proof should be prepared again for the final check by the customer. This proof is then created with exactly the same data that is also sent to the print shop. This is usually a PDF X/3:2002 file, as this is the preferred data format for printers. If the pages are delivered to the printer with bleed marks and bleed, then the proofs should actually be created in exactly the same way. The finished proofs can then first be used as approval for the customer, and secondly for checking the OK sheet in the print shop. This ensures that no unpleasant surprises wait for the customer (what does the colour look like????) or the printer (why does the customer make a complaint?????) after printing and bookbinding.
The question often arises why when creating a PDF-X/3:2002 file in Adobe Acrobat, white lines often appear in the preview when there are no lines at all in the file.
The answer is simple: In contrast to current PDF printing standards such as PDF/X-4:2010, which is exported as PDF 1.6 standard, the PDF-X/3:2002 standard often required by printers uses PDF format 1.3, in which transparency is prohibited. As a result, when you create drop shadows in Adobe InDesign, for example, they are converted into rectangular images. If such drop shadows are still used on background images, the white lines appear, which run horizontally and vertically through the PDF at the shadow points. But why do these lines disappear in print and are not visible in other applications like MacOS Preview?
Acrobat has a preview that applies anti-aliasing to vector elements to make edges as smooth as possible. However, this setting also affects paths and masks that are not actually visible at all. The pixel images of the reduced transparencies are therefore slightly blurred. And this is exactly where the white lines of the blur appear, which are actually zero in size and therefore disappear when printed on postscript-capable printers. Not PS printers partially print the screen display, whereby the lines remain disturbingly.
Most graphic artists know the effect, have postscript printers and simply live with it. However, if you are very annoyed by the white lines or if they also appear in the printout, you can simply switch off anti-aliasing in the Acrobat preferences. Under Acrobat > Preferences > Page Display you can simply deselect the checkbox “Smooth vector graphics”. This makes the edges of vector data slightly more pixelated, but the white lines of anti-aliasing disappear immediately.