RBA Premium Astrophotography

Free Tools and Plug-Ins

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.