RBA's Astrophotography

Photoshop Plug-in: RGBC

Posted: May 25th, 2010

About RGBC

RGBC is a simple Photoshop plug-in that allows you to easily and very precisely modify the weights of the red, green and blue channels in an RGB image.


To use RGBC you need a computer running Windows (tested on XP, Vista and Windows 7) and Photoshop (tested on CS2, CS3, CS4 and CS5). RGBC will likely work under previous versions of Windows and Photoshop but I haven't tested it. If you successfully run RGBC in any of the not-tested versions of Windows and/or Photoshop, let me know

Why not Mac? ... Short answer: because I don't have one, therefore I cannot compile and test the plug-in for the Mac.

Download it

Downloading RGBC is easy, simply click one the links below:

For any non-64 bits version of Photoshop: DOWNLOAD RGBC

For Photoshop 64 bits ONLY: DOWNLOAD RGBC 64bits

By the way, RGBC is free (as in "free beer") and I want it to stay that way, so permission is NOT given to include this plug-in in any commercial package. If you downloaded RGBC, whether standalone or as a part of a package, and paid for it, please let me know. Having said that, if you find it useful and would like to make a small donation, please use the "Donate" button below. This will entitle you to receive notifications of new upgrades to this plug-in. The Donate button will take you toPayPal - don't worry when you see the donation goes to AR Networks. Yes, that's me.

Installing RGBC

Once downloaded, you'll need to unzip the RGBC.zip. This will extract the RGBC.8bf file.

Once extracted, copy the RGBC.8bf file to the Plug-Ins directory in your Photoshop installation.This usually is something like C:\Program Files\Adobe\Adobe Photoshop CS2\Plug-Ins but it may be different depending on the operating system and the Photoshop version you're running.

After you've copied the file to the Plug-Ins directory, start (or restart) Photoshop.

Using RGBC

When you're ready to use RGBC (you'll need at least one image loaded in Photoshop), g the Filters menu, find the DeepSkyColors menu option, select it, then click on the RGBC sub-menu option. If you don't see it there, chances are you did something wrong when you copied the RGBC.8bf file, so double-check you indeed copied it to the right directory. Again, don't forget to restart Photoshop anytime you copy a plug-in filter to the Plug-Ins directory so Photoshop knows it's there.

From there, just enter the values you want in the R, G and B boxes, and click OK.

Does RGBC rescale my input?

Yes. Scaling in this context means that, just like if you enter the values 1:1:1, RGBC will do nothing to the image, likewise it won't do anything if you entered the values say 2:2:2. It also means that if for example you entered the values 1:2:1, RGBC will leave intact the green channel (the channel to which we assigned the value 2) and reduce by half the values for the red and blue channels, rather than leaving untouched the red and blue channels and multiply by 2 the green channel. This is done for two reasons: first, so that RGBC s regardless of thale used to calculate the offsets, and second to prevent saturation.

A note about lightness

RGBC may affect the lightness of the image, especially in cases where the "correction" is big. This is because the current version of RGBC does not operate in the CIE*Lab (or CIE*XYZ) modes that separate luminance/lightness from color data, but directly on RGB mode. Since the luminance/lightness in an RGB image is the result of combining the RGB values, any changes to any RGB channel - which is what RGBC does - will affect its luminance or lightness.

In order to preserve the exact lightness as the original image, it is recommended to follow this process:

  • Duplicate the layer where you'd like to apply RGBC.
  • Make the blending mode of that new copy to "Color".
  • Apply RGBC over that new layer.
  • Merge that new layer back with the original

The above process will adjust for color balance without affecting the lightness at all. Again, for small corrections, you could use RGBC directly over your working layer, although in general I do recommend following the method I just described.

Bit depth

RGBC should work on images of either 8, 16 or 32 bit depth. If you find that RGBC didn't work with your image, again, let me know. Regardless of the bit depth of the image, all calculations done by RGBC are done internally in 32 bit floating point mode.

Color Mode

RGBC only works well when the image is in RGB mode.  You can still use RGBC when you're in Lab or CMYK modes for example - RGBC won't complain - but the results will not be what you were expecting. Although this is something RGBC should take care of internally - say converting the image to RGB mode internally, then back to whichever mode it was before - at this point RGBC does not check the current color mode being used, and it simply assumes the image is in RGB mode, so you must make sure your image is in RGB mode prior to using RGBC. 

RGBC and masks

If you preselect an area in your image - either with the lasso tool, select range, etc. - and then run RGBC, you may be in for a disappointment when you notice that RGBC completely ignored your mask and applied the effect to the entire image. Although I guess a case could be made where one would like to modify the RGB coefficients of just one area of an image, at this point the purpose of RGBC is to modify the offsets of the RGB channels for the entire image.

If you really need to apply RGBC to just one area of the image, you can still do it by creating a duplicate layer, applying RGBC, and applying a mask to that layer.



Daniel Borcard (Contact, Page), September 23rd, 2010, 11:03

First, compliments for your incredible M42 image!
Second, is there any possibility to get a Mac version of the RGBC plugin?

Many thanks and best regards!


RBA (Contact, Page), September 23rd, 2010, 11:14
Hi Daniel,

Unfortunately this would only be possible when I get a Mac here at home. There's a chance this may be happening in the next few months, we'll see...

Sorry about that!

D. Pieter Strauss (Contact, Page), May 13th, 2011, 18:03
Can't get it to work. Message is: Could not complete the RGBC command because of a problem with the filter module interface. Photoshop CS4, Windows Vista 64 PC, installed the 64 bit version of your plugin, loaded 3 images into RBC channels. Any clues?

D. Pieter Strauss (Contact, Page), May 14th, 2011, 9:42
Now it works! However, when I apply the filter correction values (in this case R 1, G 1.458, B 1.520) I get a very blue image. The same values in CCDOps and CCDSoft give a reasonable color balance. What am I doing wrong? BTW is there a better way to ask for help than via comments?

RBA (Contact, Page), May 14th, 2011, 9:54
Pieter, I know sometimes the plug-in throws that error. I believe it has to do with a number of things related to the state of the program at tht time. For example, if you have the Channels window open and have only one channel selected, you get that error, and there may be other situations.

As for the different output compared to CCDSoft/CCDOps, I don't know how those programs do it, but maybe they do not rescale the output, while RGBC does? (read above "Does RGBC rescale my input?") ... Just a guess.

Luc Delisle (Contact, Page), October 12th, 2011, 0:32
I downloaded RGBC in my PCs3 and he is in but when I want to used it a message appear: "could not complete the RGBC command because of a problem with the filter module interface". How can I get this plug in work?

RBA (Contact, Page), October 12th, 2011, 0:42
Luc, the filter only works when it's applied to a RGB layer. For example, you may get this error if you apply the filter to just the R channel, or to a layer mask, etc.

Miguel LLoret (Contact, Page), November 3rd, 2012, 22:12
A ver si es posible bajar el pluging colocando mi nombre, correo, website y escribiendo alguna cosa aquí.

RBA (Contact, Page), November 4th, 2012, 6:32
Miguel... ¡todo soluccionado! Disculpas por las molestias.

wes (Contact, Page), June 6th, 2013, 9:41
Hello, these plugins are great, thankyou! A gradient removal tool similar to gradient terminator would be fantastic! I would happily donate!

Klaus Vollendorff (Contact, Page), August 11th, 2018, 3:37
i have installed HLVG.8bf in CS5, Plugins, Filters.
Before i habe cancelled the RGBC-plugin.

But when i start PS, the RGBC-Plugin appears.
Why that?

Best regards, Klaus

Rogelio Bernal Andreo (Contact, Page), August 24th, 2018, 9:20
Klaus, HLVG and RGBC both can be installed. One should not bother the other and both filters should appear under Filters > Deep Sky Colors

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