CNP Coffee Table Book - Interesting Printing Lessons

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CNP Coffee Table Book - Interesting Printing Lessons

Postby Ganesh H Shankar » Sun Jul 29, 2018 8:30 am

If this appears too technical read only last few paragraphs of this thread where I tried to illustrate a few things using Photoshop and images posted here at CNP. This is a very important topic if you ever want to make your own coffee table book some day in your life! ( I am yet to make one though :) )

One of the objective we had while preparing the CNP coffee table books for printing is accuracy of tonal ranges and the invariable color conversions that happen during the printing process. It took about a month for us to ensure color management aspects are taken care of as much as possible.

Most of the images we received were in Adobe RGB 1998 color space as requested. We then made first small sized proof prints of each these images on fine art Epson matt paper on Epson fine art printer to check issues with reproduction if any. We could not try CMYK based test prints initially because it was not practical from cost perspective to get test proof prints.

Interestingly colors and tonal ranges that gets rendered by these different printing technologies and papers used for printing are very different. Though we knew this theory very well during the process of making sample test prints we have learnt these interesting lessons very well now by making mistakes during sample image printing process. At times they came as big surprises. Large order book printing presses use CMYK color space for printing. CMYK space is much smaller than color spaces like AbodeRGB or sRGB that we are used to while seeing images on a display screen. Typical monitors can render all colors in sRGB color space. Wide gamut professional displays like for example Eizo monitors can reproduce close to 100% of Adobe RGB colors. Here is a comparison of a few color spaces from this Wiki page.

CIE1931xy_gamut_comparison.jpg
CIE1931xy_gamut_comparison.jpg (196.99 KiB) Viewed 1043 times


Each of those triangles show the range of colors that can be represented/rendered in that color space. Please note if don't have a wide gamut display you will not see any difference between AdobeRGB and sRGB triangles!

This one below compares AdobeRGB/sRGB profiles with one of the papers, 2200 matt paper as mentioned:

Colorspace.jpg
Colorspace.jpg (254.34 KiB) Viewed 1043 times


What this means is if you have an image which is in AdobeRGB space and has deep intense colors near the tip of the AdobeRGB color triangle then they will get mapped to colors in the tip of the 2200 matt paper profile triangle due to inevitable color conversions! This is the case if you choose any paper and any printing technology for that matter. This means your deep red/blue/intense colors that you see on your display can never get reproduced on the chosen 2200 matt paper.

Now look at the range of the CMYK space in the above first figure and compare that with sRGB or AdobeRGB space!! I hope you will understand the challenge better. The below picture from the Wiki page explains the color mapping from one space to another and the printing challenge that we have better. A given color in one space (AdobeRGB in this case) need to get mapped to nearest color in the other space (CMYK) in the below picture. In particular compare blue and green tonal ranges of the two color spaces!

RGB_and_CMYK_comparison.jpg
RGB_and_CMYK_comparison.jpg (71.43 KiB) Viewed 1043 times


Most of the printing presses use CMYK.

Now, how big an issue is this when you want your coffee table book printed? About 80% of the time there may not be much perceptible differences. At times be prepared to get (unpleasantly) surprised!!

There is a way to find that out in Photoshop whether your image will get printed properly by a printing press that uses CMYK color space.

1. Set View -> Proof Setup -> Working CMYK
2. Click on View -> Gamut Warning

When you select Gamut warning Photoshop *may* grey out certain regions of the image. This means the colors in those regions are out of CMYK gamut and print will not match what you see on the display. Then
if you select "Proof Colors" (View -> Proof Color) it will (approximately) show how the image will get rendered in the book.

Here is an example:

org_RGB.jpg
org_RGB.jpg (279.59 KiB) Viewed 1048 times


Gamut_warning.jpg
Gamut_warning.jpg (405.15 KiB) Viewed 1048 times


CMYK.jpg
CMYK.jpg (311.27 KiB) Viewed 1048 times


Often the changes may be very subtle and you may not notice it. However, there are times when the changes are very alarming. Look at this image by Prateek (please click on the thumbnail below to appreciate the differences).

image_id: 10595

How much of the image do you think is out of gamut for printing in an offset CMYK press?

Almost entire image!

Here is what you will see for gamut warning in Photoshop (greyed out regions in particular):

out_of_gamut.jpg
out_of_gamut.jpg (150.72 KiB) Viewed 1048 times


More interesting question is how will it look in the book? If you soft proof it in Photoshop for CMYK this is what you will see:

CMYK_rendered.jpg
CMYK_rendered.jpg (317.6 KiB) Viewed 1048 times


To my eyes this is a significant change between how it looks on screen vs how it might look in an offset print. Fortunately this does not happen with most of the images. Further, how the suggested appearance on the screen by Photoshop is only approximate, not exact.

However, this below image (please click on the thumbnail) by Ramesh lies completely within renderable CMYK space and should get reproduced without gamut warning for CMYK space (if the folks at printing press don't goof-up).

image_id: 8244

Another important question is how will we handle such gamut warnings? Here the options are limited. One way is to tweak the images characteristics (brightness/contrast/saturation) etc to reduce perceptible differences. However, choices are limited. We have physical limitation of what can be matched/reproduced on (different) papers itself.

I hope this gives you a feel for of what it takes to get a good print. I have explained only about what can go wrong due to scientific limitations. There are several other things that can go wrong - insufficient knowledge of working with color management (choosing the right profiles, color conversions etc.) during the printing process, to name a few. This can do more harm than scientific limitation we have.

I hope this gives you a glimpse of what we went through while preparing images we have received for the printing process!!
Ganesh H. Shankar
Wishing you best light,

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Re: CNP Book - Interesting Printing Lessons

Postby Rajkumar » Sun Jul 29, 2018 9:51 am

Thanks Ganesh for documenting....

Yes, this is the tip of the iceberg in terms of the variables and the combination in which they can manifest ... more visible in some images and more forgiving in others.....

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Re: CNP Coffee Table Book - Interesting Printing Lessons

Postby dinesh.ramarao » Mon Jul 30, 2018 8:56 am

"I hope this gives you a glimpse of what we went through while preparing images we have received for the printing process!!"

This is just 1%
:)

- RD
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Re: CNP Coffee Table Book - Interesting Printing Lessons

Postby Sriharsha Ganjam » Mon Jul 30, 2018 12:21 pm

Thanks for the insightful article Ganesh.
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