remove colour noise cast in part of an image?
 

I'm getting a green colour noise on some parts of an image when shooting a long exposure. the colour cast is not effecting the whole image just sections. How do get rid of this in photoshop?

Load your image into photoshop. Use either the magic wand/quick selection or pen tool to select the areas affected, that need correction. Next hold down the alt key, then on the bottom of the layers pallet click the "new fill or adjustment layer" (the one that is a circle half black and half grey), make sure you hold down the mouse button, then select "Hue/Saturation". In the box that appears tick the option that says "use previous layer to create clipping mask". Then hit ok.

You can now use the hue, saturation and lightness sliders to adjust the colour to another to blend in to the surroundings. I'd recommend that you always use this technique of ALT+ Adjustment Layer as it is continually editable, unlike accessing it through the main menu Image > adjustments > Hue Saturation, as these are single, permanent applications. If you want to make changes later you basically have to start again. The same applies to any of the other adjustments, whether its curves, levels, gradients etc, etc.

This is just one technique you can use. You could also highlight as before, hold alt, click "new fill adjustment layer" and then select either colour balance or channel mixer. Just remember to use the ALT + Adjustment Layer at the bottom of the layers pallet each time, as its a good habit to get into and can save you a lot of headache later.

If you are shooting RAW and using Adobe Camera RAW to process them, open the image in ACR, pick up the White Balance tool and click on something white or grey in the image. This should give you something close to what you want and you can make further adjustments from there.

[QUOTE=thefonz78;57939]I'm getting a green colour noise on some parts of an image when shooting a long exposure. the colour cast is not effecting the whole image just sections. How do get rid of this in photoshop?[/QUOTE]

I'm not sure I understand you, do you mean a colour cast as in white balance or as in green splodgy colour noise in random shadow areas?

If the later than increasing the colour slider in the noise controls if raw will help or alternativly if not a raw image then just do noise reduction on the green channel.

[QUOTE]Load your image into photoshop. Use either the magic wand/quick selection or pen tool to select the areas affected, that need correction. Next hold down the alt key, then on the bottom of the layers pallet click the "new fill or adjustment layer" (the one that is a circle half black and half grey), make sure you hold down the mouse button, then select "Hue/Saturation". In the box that appears tick the option that says "use previous layer to create clipping mask". Then hit ok.[/QUOTE]

thefonz hope you got your shot sorted out but I would like to say thanks to amk great tip just been using it .

Thanks Mark

You're welcome Mark. Glad you found it useful :)

Second that Mark, amk regularly posts advice and help with photoshop and will likely be doing more having instigated a discussion to incorporate a new section of the forum for doing just this sort of thing.
For those unaware of amk's lobbying, see [URL="http://www.photoradar.com/forums/showthread.php?t=6690"][B]here[/B][/URL].

I not getting colour cast in the whole image just patches so thanks amk i will try this tip.