Nihil obstat quominus imprimatur
From InDesign, creating a PDF for printing takes 4 clicks: a few steps that can hide pitfalls or errors that can compromise the whole job. And yet, obtaining a perfect file for printing is not that complex; just a few steps and a couple of checks are enough to avoid surprises after the longed-for ‘Seen, print!’.
by Lorenzo Capitani
The colour space
Not all the colours in a digital or digitised photo can be reproduced in print. This is a fact inherent in the way printing reproduces colours. In contrast to the RGB space where colours are represented by light by additive synthesis (all colours added together give white), in offset or digital printing, printing is done using 4 basic inks (Cyan, Magenta, Yellow, Key-Black) by subtractive synthesis (the 4 colours added together give black). Theoretically, the colours Cyan, Magenta, and Yellow can reproduce all the others when combined. Maximum brightness is achieved by the total absence of inks and thus corresponds to paper white. When the first three colours are added together, the result is not pure black but a very dark brown. The colour K or black is used to remove light from the printed image altogether, which is why the eye perceives the colour as black. The problem arises when one has to switch to the CMYK print space from the RGB of the acquisition device (camera or scanner) or RGB reproduction device (the monitor) capable of representing many more colours and in different ranges. Obvious things, you might say, and yet 50% of problems in pre-printing and printing arise precisely from this conversion, which is often done without awareness as if it were just a click to do. Conversion from RGB to CMYK hardly ever happens without differences. Complicating matters is that printing is now only one of the possible outputs and the only one that requires this colour space; the rest, everything digital, remains in RGB. Then there is the added problem of when to do the conversion: upstream before typesetting or downstream before the final output? The first approach is only valid in theory: while it gives the illusion of having everything under control, it is also limiting. If we convert a photo destined for printing and other channels to four-colour before post-producing it - so that we have the same range of reproducible colours, which in any case remains filtered by the monitor - we will still have to revert to RGB to be able to use otherwise unavailable Photoshop tools and filters and to use that photo in the digital environment. Then it is better to post-produce in RGB, creating a sort of master from which to start for each channel provided and only proceed with the conversion to CMYK when necessary, i.e. when the photo begins its process to be printed. The image must be considered part of an extensive process in which not all outputs are immediately declared and may differ considerably, so one must be as conservative as possible, never losing information. Similarly, converting at the output, i.e., when making the PDF, can be risky because the colours of a photo may not be as we wanted them, and there is often no time to rectify this.
So the suggestion is to convert before going out to PDF. For printed material in the fashion sector, we would check all the photos in Photoshop one by one. For a commercial brochure, converting to output will suffice as long as we have the foresight to choose the ‘Convert to Target’ function and the target profile in the Output window of the ‘Export PDF’ command in InDesign; if we don't do this, what was in RGB will arrive in print.
Pay attention to the colours of all other graphics, such as backgrounds, fillets and texts. Before making the PDF, therefore, a look at the Samples palette will avoid problems. Eliminate colours not in use, convert RGB and, if the job does not involve them, convert spot colours to a four-colour process according to the nearest values. If the job is very complex and you find a spot colour in use not visible on the page, remember that ‘Preview colour selections’ InDesign shows where it is used. Pay attention to black text, which must be in black only and not in 4 colours, and to colours imported from links. A vector logo, for example, carries its colours in its colour space, which are not shown in InDesign's Samples and, as such, pass into the PDF.
Finally, there remains the issue of which RGB to use - sRGB or Adobe RGB. The comparison of gamuts gives us the answer with a necessary premise: in no case do the RGB spaces contain CMYK, so it is a matter of making a choice knowing that it will still be an approximation. Although sRGB has a relatively narrow gamut and is therefore theoretically more conservative than CMKY, it far exceeds the print space in many colour areas, with one glaring exception: the area between green and cyan, so much so that print cyan is not included in sRGB. This means that sRGB does not allow the full gamut available in CMYK to be exploited. Adobe RGB, however, cannot fully encompass CMYK either, but the approximation you get is far better. So Adobe RGB is the best choice for offset. And for digital printing? In addition to CMYK inks, which perform better in digital than traditional four-colour inks because they are more intense and pure, light cyan or light magenta inks are often used to extend the range of reproducible colours. Obviously, no digital printing press can work in RGB for physical reasons, but its colour space is broader than that of the traditional four-colour process; for all these reasons, however, Adobe RGB is the best compromise.
The Image Format
According to a report published this year by W3Techs, a company that provides statistics on how websites are created and managed through completely impartial research, 80% of the images used on websites are PNG or JPEG. These formats, apart from their use on the net, are also the most widely used in general for images for printing: after all, cameras and scanners have these formats among their available outputs, which, besides being relatively light to transfer, process and archive, have in fact supplanted tiff and eps. The problem with JPEG (or JPG in the Windows world) is that it is a lossy format. Translated: if the only photo I have available is in this format, I have no alternative and will have to make do. But if I have the opportunity to shoot with professional hardware, it makes no sense to use this format because shooting directly in JPEG already means giving up the highest possible quality. Pro cameras, but also the iPhone, even if set up to shoot directly in JPEG, shoot in raw and convert automatically without the possibility of intervention or adjustment: they, therefore, perform a complete transformation, correct perhaps from a mathematical point of view, but still arbitrary. The JPEG has won over other formats because it has a very high level of compression and can transform very large images into much smaller files with low consumption of space and memory, and it does so by eliminating all colour ranges theoretically not visible to the human eye, exploiting the principle of predictors that attempts to estimate the value of a colour from adjacent or already processed ones. This means an image with a continuous background can be highly compressed because, between one colour sample and another adjacent one, the intermediate sample will be very similar and, as such, eliminable. Beware that compression application occurs each time the image is saved, even if imperceptibly, the image loses quality. In general, JPEG is unsuitable for images with text, drawings, diagrams and graphics, plus it does not support tracings and transparencies, as PNG does. Ideally, the best thing would be to always shoot with a professional digital camera, in raw, develop the raw with all adjustments off-camera, and save in tiff in RGB.
Raw has 16,388 levels of brightness for 16-bit images, whereas JPEG only has 256: this is evident on darker images where you need to recover shadow areas. Shall we carry out an experiment? Shoot first in raw and then in JPEG with the same camera and the same settings a completely black object, open the two files in Camera Raw and increase the exposure by 5 stops: the raw will appear as a uniform pattern, the JPEG will show areas of the same colour, bands, stripes, artefacts... (see image folder/ raw vs JPEG comparison).
Finally, post-produce and layout the tiff: only in this way will we ensure that we are working without significant data loss because the tiff is precisely the list of pixels in the image.
Be careful not to use PNG, which, although it is not lossy, supports the alpha channel for transparencies and uses compression techniques that do not sacrifice quality or original detail (at least PNG-24) but cannot be saved in CMYK, which means converting to PDF according to profile, without any control and in an arbitrary manner.
The right resolution
Let's face it, the 300 DPI that all tutorials recommend for printing is more of a simplification than an actual necessity. Rather than high or low resolution, one should speak of the proper resolution for what is to be printed. And so, partly because more brochures are printed than posters, partly because it is better to have more DPI than less to avoid low-quality images, 300 DPI has become the resolution that any image must have to be printed. And here the distinctions begin. Without going into the resolution/linear ratio for which I refer to Marco Olivotto's excellent article ‘Russell's teapot and Photoshop’, easily available online, everything depends on the enlargement that a photo will have on the page: paradoxically, very large images at very high resolutions give effects such as moiré. A 72 DPI photo, perhaps taken from the web - very large, e.g. 2560x1600 px, i.e. 90 cm base - becomes 21 cm if taken at 300 DPI and thus sustains an A4 without any problems if kept at natural size. Without getting lost in proportions, the trick to understanding whether a low-resolution image, between 72 and 96 DPI, can be used for printing is to divide the measurement in cm by 3.5. Resizing from 72 to 300 DPI, however, must be done without resampling: formally, you get a high resolution with the right size and DPI, but qualitatively the photo remains of low quality! In InDesign, we are helped by the Links palette, which summarises object by object, colour profile, original DPI and actual DPI according to enlargement.
What happens to our photo, left at 72 or switched to 300 DPI, when it is put on an A4 double page? It will have an effective resolution of 144 DPI, which is too small. If you just can't use another photo, all that's left is to use Photoshop's recent Retain Details 2.0 feature, which uses an algorithm designed to detect and preserve the most important details and textures in images without introducing excessive sharpening of protruding edges or smoothing out low-contrast details, and also improves the preservation of intricate details such as text and logos without amplifying noise or creating artefacts. You won't achieve miracles or make a low a high, but the quality will improve. Just as it will improve if you use the Enhance/Super Resolution command available in Camera Raw from version 13.2, which promises to double the resolution of an image. No magic, just advanced handling of the method behind the Enhance Detail released in 2019. Super Resolution does an excellent job of interpolation, providing a significant edge over other already available methods. Obviously, it cannot add detail that does not exist, but it uses artificial intelligence and machine learning that learns from surrounding details to improve and increment the 'apparent resolution'.
But it is not only the size of the image that matters; the distance from which the image will be viewed must also be taken into account: a picture in a book is one thing, and a poster in the street is another. From the distance, you derive the resolution for a good quality print.
The formula says:
resolution (PPI) = 8.733 / viewing distance (cm)
Finally, up to this point, we have talked about DPI, or dots per inch, but we should more correctly talk about PPI, pixels per inch. Theory says that ‘dots’ are the dots of ink that a printer deposits on the paper, and ‘per inch’ indicates how many such dots the printer can produce along a line 1 inch long; obviously, this depends on the technology, and it is not always true that one dot corresponds to 1 pixel. In short, the PPI tells us how many pixels per inch a device can represent or, in other words, what the printed size of an image of a given size will be on a specific device with a particular resolution. Complex? That's why we tend to bring everything back to the equation:
print = 300 DPI, video = 72 DPI.
Fonts
Let's now get to fonts, the blessing and curse of every graphic and RIP. The road to standardisation is still long, and it is not uncommon to come across very old PostScript Type 1 fonts from archives that graphic designers exchange in defiance of licences or old layouts. After 40 years, Adobe will end support for Type 1 fonts in January 2023. Although some operating systems still support the use of Type 1 fonts, they are no longer supported in many crucial environments for modern platforms, including web browsers and mobile operating systems. On that date, updated Adobe applications will not recognise the presence of Type 1 fonts: even if they are installed in the operating system, they will not be displayed in the Fonts menu, it will not be possible to use them, and any existing Type 1s in the document will be displayed as 'Missing Fonts'. Adobe provides the updated OpenType version for Type 1s that you have a regular licence for, whereas, for non-Adobe fonts, you must contact other manufacturers. Conversion is possible with third-party software such as TransType, FontXchange or Fontlab Studio. Just beware that the conversion is not always perfect: glyphs, special characters or diacritical marks are not always rendered correctly.
It is therefore always better to use OpenType fonts, the only ones compatible with the Mac and Windows world, and guarantee full exportability to digital formats. Here, too, InDesign with the Find Font command helps identify the fonts correctly installed on the machine and therefore available for PDF creation and to check the format type. By now, it is also possible to find old fonts in OpenType, and all free online font libraries (e.g. www.google.com/fonts) are available in this format. If necessary, it remains possible to convert them. In this case, if it is impossible to replace the font with a similar one, one can resort to the extreme measure of a conversion to a layout (create profiles on the text box). This is a drastic solution that does not allow retroversion in case of corrections. Place a copy of the text cage off the page for possible changes if necessary.
Bleeds and overprinting
One of the most frequently recurring oversights is the lack of bleeds for graphic elements that go into the bleed area and exceed the cut. Overprinting is indispensable for avoiding unsightly white threads in the case of an inaccurate cut. 3-5 mm are sufficient and can be recovered without any problems by moving the photo slightly, enlarging it, or just remembering to open the cage. All this without even stretching the bottom. The oversight stems from the fact that those who layout prefer to see the page exactly as it will be to assess the weights and balances of the elements. It would be enough to get in the habit - as soon as the layout is created – of indicating a page bleed of at least 3 mm to have guides on each side, open all cages at least 3 mm and set the document view as Preview when you want to evaluate the page bleed.
Finally, an insidious setting can compromise the rendering of a printout: changing the perforation and overprint colour settings. Fortunately, InDesign natively sets how colours should interact with each other correctly. If you have not changed the transparency of the graphics with the Transparency panel, fills and traces will appear solid as the top colour perforates, i.e. cuts away, the underlying area at the points of intersection. InDesign allows the simulation of overprinting to check the effect. While all colours perforate, black (K 100), applied to text or objects by default, is overprinted to overcome the out-of-register on small black characters placed on top of coloured areas. You can change the black ink settings in the Black Appearance preferences, but this should only be done if the black works on a large area (e.g. very large text) that sits on top of a coloured object, such as a photo, to prevent it from showing through underneath: this is because black ink is usually printed last and may not be totally opaque. To be sure of how the output will look, just check the PDF in Acrobat with Output Preview. In the separations window, you can see how the individual inks work, whether chromatic or Pantone, plate by plate, and their opacity. You can also check the correct perforation from this palette with ‘Simulate overprinting’. Always leave the monitor simulation of overprints activated in the Acrobat preferences.
Preliminary checking
Up to this point, we have seen small steps for correctly creating a file to export an accurate PDF for printing. But it is always possible to check compliance with the standards in the course of work by taking advantage of Preflight tools such as InDesign's live Preliminary Verification or Acrobat's counterpart that directly checks the PDF. In both cases, the tool uses a series of profiles according to the output for which the work is intended. Unfortunately, in InDesign, there is only the [basic] profile in which colours and resolutions are not controlled. If you don't want to create your own profile, which is also very easy, you can download the GWG Live Preflight profiles for Adobe InDesign from the Ghent Workgroup website (http://tiny.cc/5xaquz). The preliminary check configured in this way checks the file live, indicating with a traffic light at the bottom of the programme window if there are any errors and where so that you can intervene.
In Acrobat, on the other hand, the check must be called up from the Print Production menu: here, there are many pre-installed profiles, including those for offset printing with and without spot colours and all those for checking according to ISO certifications, such as PDF/x. Usually, it is sufficient to check a PDF with the sheetfed offset profile for compatibility with the Ghent Workgroup specifications. The result will be a detailed report in which errors and alerts are listed and dynamically linked directly to the object on the page. Just be aware that the tool also allows you to automatically correct errors, which you should do with awareness, especially in the case of colour space conversions or covering or perforation settings
by Lorenzo Capitani
The colour space
Not all the colours in a digital or digitised photo can be reproduced in print. This is a fact inherent in the way printing reproduces colours. In contrast to the RGB space where colours are represented by light by additive synthesis (all colours added together give white), in offset or digital printing, printing is done using 4 basic inks (Cyan, Magenta, Yellow, Key-Black) by subtractive synthesis (the 4 colours added together give black). Theoretically, the colours Cyan, Magenta, and Yellow can reproduce all the others when combined. Maximum brightness is achieved by the total absence of inks and thus corresponds to paper white. When the first three colours are added together, the result is not pure black but a very dark brown. The colour K or black is used to remove light from the printed image altogether, which is why the eye perceives the colour as black. The problem arises when one has to switch to the CMYK print space from the RGB of the acquisition device (camera or scanner) or RGB reproduction device (the monitor) capable of representing many more colours and in different ranges. Obvious things, you might say, and yet 50% of problems in pre-printing and printing arise precisely from this conversion, which is often done without awareness as if it were just a click to do. Conversion from RGB to CMYK hardly ever happens without differences. Complicating matters is that printing is now only one of the possible outputs and the only one that requires this colour space; the rest, everything digital, remains in RGB. Then there is the added problem of when to do the conversion: upstream before typesetting or downstream before the final output? The first approach is only valid in theory: while it gives the illusion of having everything under control, it is also limiting. If we convert a photo destined for printing and other channels to four-colour before post-producing it - so that we have the same range of reproducible colours, which in any case remains filtered by the monitor - we will still have to revert to RGB to be able to use otherwise unavailable Photoshop tools and filters and to use that photo in the digital environment. Then it is better to post-produce in RGB, creating a sort of master from which to start for each channel provided and only proceed with the conversion to CMYK when necessary, i.e. when the photo begins its process to be printed. The image must be considered part of an extensive process in which not all outputs are immediately declared and may differ considerably, so one must be as conservative as possible, never losing information. Similarly, converting at the output, i.e., when making the PDF, can be risky because the colours of a photo may not be as we wanted them, and there is often no time to rectify this.
So the suggestion is to convert before going out to PDF. For printed material in the fashion sector, we would check all the photos in Photoshop one by one. For a commercial brochure, converting to output will suffice as long as we have the foresight to choose the ‘Convert to Target’ function and the target profile in the Output window of the ‘Export PDF’ command in InDesign; if we don't do this, what was in RGB will arrive in print.
Pay attention to the colours of all other graphics, such as backgrounds, fillets and texts. Before making the PDF, therefore, a look at the Samples palette will avoid problems. Eliminate colours not in use, convert RGB and, if the job does not involve them, convert spot colours to a four-colour process according to the nearest values. If the job is very complex and you find a spot colour in use not visible on the page, remember that ‘Preview colour selections’ InDesign shows where it is used. Pay attention to black text, which must be in black only and not in 4 colours, and to colours imported from links. A vector logo, for example, carries its colours in its colour space, which are not shown in InDesign's Samples and, as such, pass into the PDF.
Finally, there remains the issue of which RGB to use - sRGB or Adobe RGB. The comparison of gamuts gives us the answer with a necessary premise: in no case do the RGB spaces contain CMYK, so it is a matter of making a choice knowing that it will still be an approximation. Although sRGB has a relatively narrow gamut and is therefore theoretically more conservative than CMKY, it far exceeds the print space in many colour areas, with one glaring exception: the area between green and cyan, so much so that print cyan is not included in sRGB. This means that sRGB does not allow the full gamut available in CMYK to be exploited. Adobe RGB, however, cannot fully encompass CMYK either, but the approximation you get is far better. So Adobe RGB is the best choice for offset. And for digital printing? In addition to CMYK inks, which perform better in digital than traditional four-colour inks because they are more intense and pure, light cyan or light magenta inks are often used to extend the range of reproducible colours. Obviously, no digital printing press can work in RGB for physical reasons, but its colour space is broader than that of the traditional four-colour process; for all these reasons, however, Adobe RGB is the best compromise.
The Image Format
According to a report published this year by W3Techs, a company that provides statistics on how websites are created and managed through completely impartial research, 80% of the images used on websites are PNG or JPEG. These formats, apart from their use on the net, are also the most widely used in general for images for printing: after all, cameras and scanners have these formats among their available outputs, which, besides being relatively light to transfer, process and archive, have in fact supplanted tiff and eps. The problem with JPEG (or JPG in the Windows world) is that it is a lossy format. Translated: if the only photo I have available is in this format, I have no alternative and will have to make do. But if I have the opportunity to shoot with professional hardware, it makes no sense to use this format because shooting directly in JPEG already means giving up the highest possible quality. Pro cameras, but also the iPhone, even if set up to shoot directly in JPEG, shoot in raw and convert automatically without the possibility of intervention or adjustment: they, therefore, perform a complete transformation, correct perhaps from a mathematical point of view, but still arbitrary. The JPEG has won over other formats because it has a very high level of compression and can transform very large images into much smaller files with low consumption of space and memory, and it does so by eliminating all colour ranges theoretically not visible to the human eye, exploiting the principle of predictors that attempts to estimate the value of a colour from adjacent or already processed ones. This means an image with a continuous background can be highly compressed because, between one colour sample and another adjacent one, the intermediate sample will be very similar and, as such, eliminable. Beware that compression application occurs each time the image is saved, even if imperceptibly, the image loses quality. In general, JPEG is unsuitable for images with text, drawings, diagrams and graphics, plus it does not support tracings and transparencies, as PNG does. Ideally, the best thing would be to always shoot with a professional digital camera, in raw, develop the raw with all adjustments off-camera, and save in tiff in RGB.
Raw has 16,388 levels of brightness for 16-bit images, whereas JPEG only has 256: this is evident on darker images where you need to recover shadow areas. Shall we carry out an experiment? Shoot first in raw and then in JPEG with the same camera and the same settings a completely black object, open the two files in Camera Raw and increase the exposure by 5 stops: the raw will appear as a uniform pattern, the JPEG will show areas of the same colour, bands, stripes, artefacts... (see image folder/ raw vs JPEG comparison).
Finally, post-produce and layout the tiff: only in this way will we ensure that we are working without significant data loss because the tiff is precisely the list of pixels in the image.
Be careful not to use PNG, which, although it is not lossy, supports the alpha channel for transparencies and uses compression techniques that do not sacrifice quality or original detail (at least PNG-24) but cannot be saved in CMYK, which means converting to PDF according to profile, without any control and in an arbitrary manner.
The right resolution
Let's face it, the 300 DPI that all tutorials recommend for printing is more of a simplification than an actual necessity. Rather than high or low resolution, one should speak of the proper resolution for what is to be printed. And so, partly because more brochures are printed than posters, partly because it is better to have more DPI than less to avoid low-quality images, 300 DPI has become the resolution that any image must have to be printed. And here the distinctions begin. Without going into the resolution/linear ratio for which I refer to Marco Olivotto's excellent article ‘Russell's teapot and Photoshop’, easily available online, everything depends on the enlargement that a photo will have on the page: paradoxically, very large images at very high resolutions give effects such as moiré. A 72 DPI photo, perhaps taken from the web - very large, e.g. 2560x1600 px, i.e. 90 cm base - becomes 21 cm if taken at 300 DPI and thus sustains an A4 without any problems if kept at natural size. Without getting lost in proportions, the trick to understanding whether a low-resolution image, between 72 and 96 DPI, can be used for printing is to divide the measurement in cm by 3.5. Resizing from 72 to 300 DPI, however, must be done without resampling: formally, you get a high resolution with the right size and DPI, but qualitatively the photo remains of low quality! In InDesign, we are helped by the Links palette, which summarises object by object, colour profile, original DPI and actual DPI according to enlargement.
What happens to our photo, left at 72 or switched to 300 DPI, when it is put on an A4 double page? It will have an effective resolution of 144 DPI, which is too small. If you just can't use another photo, all that's left is to use Photoshop's recent Retain Details 2.0 feature, which uses an algorithm designed to detect and preserve the most important details and textures in images without introducing excessive sharpening of protruding edges or smoothing out low-contrast details, and also improves the preservation of intricate details such as text and logos without amplifying noise or creating artefacts. You won't achieve miracles or make a low a high, but the quality will improve. Just as it will improve if you use the Enhance/Super Resolution command available in Camera Raw from version 13.2, which promises to double the resolution of an image. No magic, just advanced handling of the method behind the Enhance Detail released in 2019. Super Resolution does an excellent job of interpolation, providing a significant edge over other already available methods. Obviously, it cannot add detail that does not exist, but it uses artificial intelligence and machine learning that learns from surrounding details to improve and increment the 'apparent resolution'.
But it is not only the size of the image that matters; the distance from which the image will be viewed must also be taken into account: a picture in a book is one thing, and a poster in the street is another. From the distance, you derive the resolution for a good quality print.
The formula says:
resolution (PPI) = 8.733 / viewing distance (cm)
Finally, up to this point, we have talked about DPI, or dots per inch, but we should more correctly talk about PPI, pixels per inch. Theory says that ‘dots’ are the dots of ink that a printer deposits on the paper, and ‘per inch’ indicates how many such dots the printer can produce along a line 1 inch long; obviously, this depends on the technology, and it is not always true that one dot corresponds to 1 pixel. In short, the PPI tells us how many pixels per inch a device can represent or, in other words, what the printed size of an image of a given size will be on a specific device with a particular resolution. Complex? That's why we tend to bring everything back to the equation:
print = 300 DPI, video = 72 DPI.
Fonts
Let's now get to fonts, the blessing and curse of every graphic and RIP. The road to standardisation is still long, and it is not uncommon to come across very old PostScript Type 1 fonts from archives that graphic designers exchange in defiance of licences or old layouts. After 40 years, Adobe will end support for Type 1 fonts in January 2023. Although some operating systems still support the use of Type 1 fonts, they are no longer supported in many crucial environments for modern platforms, including web browsers and mobile operating systems. On that date, updated Adobe applications will not recognise the presence of Type 1 fonts: even if they are installed in the operating system, they will not be displayed in the Fonts menu, it will not be possible to use them, and any existing Type 1s in the document will be displayed as 'Missing Fonts'. Adobe provides the updated OpenType version for Type 1s that you have a regular licence for, whereas, for non-Adobe fonts, you must contact other manufacturers. Conversion is possible with third-party software such as TransType, FontXchange or Fontlab Studio. Just beware that the conversion is not always perfect: glyphs, special characters or diacritical marks are not always rendered correctly.
It is therefore always better to use OpenType fonts, the only ones compatible with the Mac and Windows world, and guarantee full exportability to digital formats. Here, too, InDesign with the Find Font command helps identify the fonts correctly installed on the machine and therefore available for PDF creation and to check the format type. By now, it is also possible to find old fonts in OpenType, and all free online font libraries (e.g. www.google.com/fonts) are available in this format. If necessary, it remains possible to convert them. In this case, if it is impossible to replace the font with a similar one, one can resort to the extreme measure of a conversion to a layout (create profiles on the text box). This is a drastic solution that does not allow retroversion in case of corrections. Place a copy of the text cage off the page for possible changes if necessary.
Bleeds and overprinting
One of the most frequently recurring oversights is the lack of bleeds for graphic elements that go into the bleed area and exceed the cut. Overprinting is indispensable for avoiding unsightly white threads in the case of an inaccurate cut. 3-5 mm are sufficient and can be recovered without any problems by moving the photo slightly, enlarging it, or just remembering to open the cage. All this without even stretching the bottom. The oversight stems from the fact that those who layout prefer to see the page exactly as it will be to assess the weights and balances of the elements. It would be enough to get in the habit - as soon as the layout is created – of indicating a page bleed of at least 3 mm to have guides on each side, open all cages at least 3 mm and set the document view as Preview when you want to evaluate the page bleed.
Finally, an insidious setting can compromise the rendering of a printout: changing the perforation and overprint colour settings. Fortunately, InDesign natively sets how colours should interact with each other correctly. If you have not changed the transparency of the graphics with the Transparency panel, fills and traces will appear solid as the top colour perforates, i.e. cuts away, the underlying area at the points of intersection. InDesign allows the simulation of overprinting to check the effect. While all colours perforate, black (K 100), applied to text or objects by default, is overprinted to overcome the out-of-register on small black characters placed on top of coloured areas. You can change the black ink settings in the Black Appearance preferences, but this should only be done if the black works on a large area (e.g. very large text) that sits on top of a coloured object, such as a photo, to prevent it from showing through underneath: this is because black ink is usually printed last and may not be totally opaque. To be sure of how the output will look, just check the PDF in Acrobat with Output Preview. In the separations window, you can see how the individual inks work, whether chromatic or Pantone, plate by plate, and their opacity. You can also check the correct perforation from this palette with ‘Simulate overprinting’. Always leave the monitor simulation of overprints activated in the Acrobat preferences.
Preliminary checking
Up to this point, we have seen small steps for correctly creating a file to export an accurate PDF for printing. But it is always possible to check compliance with the standards in the course of work by taking advantage of Preflight tools such as InDesign's live Preliminary Verification or Acrobat's counterpart that directly checks the PDF. In both cases, the tool uses a series of profiles according to the output for which the work is intended. Unfortunately, in InDesign, there is only the [basic] profile in which colours and resolutions are not controlled. If you don't want to create your own profile, which is also very easy, you can download the GWG Live Preflight profiles for Adobe InDesign from the Ghent Workgroup website (http://tiny.cc/5xaquz). The preliminary check configured in this way checks the file live, indicating with a traffic light at the bottom of the programme window if there are any errors and where so that you can intervene.
In Acrobat, on the other hand, the check must be called up from the Print Production menu: here, there are many pre-installed profiles, including those for offset printing with and without spot colours and all those for checking according to ISO certifications, such as PDF/x. Usually, it is sufficient to check a PDF with the sheetfed offset profile for compatibility with the Ghent Workgroup specifications. The result will be a detailed report in which errors and alerts are listed and dynamically linked directly to the object on the page. Just be aware that the tool also allows you to automatically correct errors, which you should do with awareness, especially in the case of colour space conversions or covering or perforation settings
02/09/2022
