Adobe Photoshop (for this little How-To, we used Photoshop CS3 by Adobe on the Apple Mac platform) Because Fringing occurs when light is split around edges of certain object and materials, we ussually know that we have only to control a very narrow colour band in order to remove it.
In my example, we shot a poker game in studio, with controlled studio lighting, a Canon 5DmkII and EF 24-70mm f/2.8L lens. As you can see, it’s a controlled situation, with pretty decent equipment. However, the cards we used kept on giving us purple fringing, even on underexposed images, and best we could figure out is that it came from the plastic/wax coating that protects the cards. Switching to a worn, well played and well used deck solved the problem, but left us with damaged cards in the shots, so we decided to handle the fringing in post.
As you can see from the image we picked up a very decent fringe (image enlarged to 200%) even on the slight embossed area where the back graphic on the card is printed. So the first step is to isolate that colour range:
Open th image you want to work in in photoshop (or your graphics program, most will have similar abilities) and zoom into the area where the Chromatic Aberation is prominent.
Create a Hue/Saturation adjustment layer.
You will notice that the layer also gives you a “Reveal all” (or White) mask. That means that all adjustments you make will be visible all over the image.
Along with your adjustment layer, the Hus/Saturation Dialogue box should have popped open (if you closed it, or it didn’t open, no worries, simply double click on the Hue/Sat icon on the adjustment layer, and it will be back)
Because of the nature of CA (as mentioned earlier) we can safely assume that the most effective are to work in would be the Blue Colour Layers, so instead of working in the “Master” (all colour ranges) areas, choose “Blue from the Dropdown Options.
Choose the left-most eyedropper, and a target should appear (as your mouse pointer) You can now move over to your image and make a range selection for the colour we want to control.
…. now it’s simply a matter of reducing saturation (and a slight “lightness” if necesarry) untill you have a fairly normal tone. be carefull to push it too far, as you will end up with a grey strip or “halo”where the Purple Fringe was.
Note: You will notice that sometimes you have 2 prominent colours, like a Purple and a Cyan, so you might need to do this processtwice with 2 adjustment layers, each with it’s own colour range.
Now this is the important part. Because we were working on a mask that “revealed”our changes over the whole image, all the Blue/Purple coloured areas in the image (Like the pattern print on the bak of the card) would have been affected. we now need to go and “hide” the changes to those areas so that we have the original colours in our image.
This we do by simply going to the Mask Icon on the adjustment layer and clicking on it to select that as our working area.
As we were working in a “Reveal All” mode (or a white mask) we need to now choose Black as a colour and our paintbrush tool to do the rest of the work.
Now it’s simply a matter of painting black everywhere you want the original blue/purple colour to show up in your image. If you actually see Black lines appearing on your image, it means you have not selected the white MASK icon on the adjustment layer.
Just undo the painting, go back to the adjustment layer, and click on the MASK icon (a small fram will appear around it to signal that it’s selected)
Now as the song goes… just paint it black!
Be carefull of the CA areas, if you accidently paint over an area and the Purple Fringe shows up again, simply change your colour of your brush to white, and clean up the mistake, change back to colour black and complete the image (in the image above you can see that we are bringing back the nice blue printing on the card, but the edges of the cards are now clean and free from the purple fringes.
All images Copyright Sean Nel 2009~