Thursday, July 15, 2021

Non-Photo Blue and GIMP

Recently a client asked me to help with removing non-photo blue graph lines from a hand-drawn diagram she would be using in the book she was writing. 

As most of my readers already know, I don't have an account with Adobe, and I refuse to "rent" their overpriced programs. (Adobe does not allow you to buy Photoshop, Illustrator, InDesign, and their other exclusive software. I thought it was overpriced then, now, it cost more per year just to "subscribe" and use their software online.) OK... I'll get off my soapbox. The bottom line is that I work mostly with GIMP, an open source, cross-platform image editor. 

I have found that GIMP can do almost anything I need it to do when it comes to image cleanup, photo manipulation, and the like. The BIG difference, is that GIMP uses RGB colors, where Photoshop can use CMYK.

If you don't know what that means, here's a quick and overly simplified explanation. 

The biggest difference is that CMYK is used for print and RGB is used mostly in digital media. 

CMYK are the INKS used by printers. Cyan Magenta, Yellow, and Black. (K stands for Key plate, which in traditional color separation printing, is the plate that holds the detail in the image done in BLACK ink.) Simply put, the more ink colors, the darker the image prints.

RGB is opposite of this process. Images on our computer screen or on TV use light waves, various intensities of Red, Green, and Blue light. The more light you add the brighter the color, and if you mix all three you get pure white light.

With such incredible advancements in computer technology over the last 3 decades, I realized that I have taken for granted that whatever image I create on the screen is "magically" converted to print beautifully on my Cyan, Magenta, Yellow, and Black Canon all-in-one office printer or to show up clearly when uploaded to a website, no matter what program I used to create it.

Getting back to my dilemma...

Originally, NPB (Non-Photo-Blue) would not be picked up by a Stat Camera and the camera would create a "Print Ready" image. Traditional Non-Photo-Blue pencils, and in my clients case, Non-Photo-Blue graph lines, can be easily removed by using the CMYK color separation process used by Photoshop. By removing the Cyan, and combining the rest of the colors, we are left with a black image with no graph lines. 

This easy fix is not available in the RGB color process used by GIMP. But I was not giving up. I buckled down and did a whole bunch of research. I scoured the GIMP forums and YouTube videos for days looking for a workaround. I finally found it. 

Overcoming this problem took a quite a bit more computer/programing understanding. This is not for the beginner, or those who only use a computer to check email, social media and watch TV. But for those tech savvy designers who have run into this problem with no way to solve it... this workaround is absolutely worth it. 

According to the artist's visual infographic below, they did not use a plugin, BUT I learned that I did actually need the plugin Separate+. I did a Google search for the "GIMP plugin Separate+ 0.5.8 download", found it a GIMP forum that I trust and installed it for my Windows operating system per the instructions. GIMP is a open source software, manning that any programmer can write code for the program. While most coders are typically honest, good people, you should also be aware that downloading and running any software could have the potential to contain malicious code, such as viruses and malware. It is always very good to follow this advice.

  • Be sure to have a current backup of your computer just in case
  • Download plugins only from a trusted site or source
  • Use your computer security software to check the file before installing

You will also need to add the CMYK color management ICC profile to GIMP. These ICC profiles used to be available straight from Adobe, but I was greeted with "This site can't be reached" or a 404 error message, on the Adobe site. Most computers have this, and other color profiles already installed into the printer software. Doing a search on my computer for "cmyk.icc", I found the file and COPIED it into GIMP color profile folder. (This folder path is different depending on what kind of operating software you are using and how you installed GIMP originally.)

Once you have installed the plugin and added the CMYK profile to GIMP, restart your computer and then you are ready to go.  

Now that the difficult part is done, here is how to remove Cyan from a GIMP image. I found this infographic on Deviantart of all places! 

Until next time, keep on keepin' on....

How to Remove Non-Photo Blue in GIMP

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