Fringing

[Tracey McGovern]

Hi

I went out this morning armed with camera. Came across some crocuses, took a few shots, some were purple and a some were white, all of the flowers have come out with blue fringing round them, could anyone explain why?

This shot is streight out of the camera, I shot it in RAW but have converted it to jpg for uploading. I have not done any other modifications to it, I have also included the metadata.

IMG_1022-Web.jpg (106.98 KiB) Viewed 5835 times

IMG_1022 Metadata.jpg (183.1 KiB) Viewed 5835 times

Any advice would be appreciated.

Thanks
Tracey

[John]

Fringing occurs when different colours are focused at different points by the lens - this is a form of chromatic aberration. Most of the time it goes unnoticed, but in some situations it is more obvious. One is branches against sky, where the high contrast shows the fringing along the branches.

In this case, it may be a combination of higher contrast and the reflectivity of blue flowers. On film, blue flowers seldom looked the proper colour because they reflected UV light and this affected the film. With digital cameras this isn't the same and blues are generally excellent. However, with perhaps a kit lens, which may not be as fully corrected as some more expensive ones, if there's a lot of UV light about it may be causing your problem.

This fringing should be correctable to some degree in ACR or your other RAW converter. You could also desaturate the blues slightly, which will also help.

Hope that helps!

[Theo Dibbits]

Tracey

The bad new is:

In digital sensors, axial CA results in the red and blue planes being defocused (assuming that the green plane is in focus), which is relatively difficult to remedy in post-processing

The good news is:

Due to the Canon EF lens mount all-electronic lens communication and coupling system, the Canon's Digital Photo Professional software has one of the most advanced chromatic aberration appearance minimization (also vignetting and distortion handling) systems that uses lens model-specific focusing distance, focal length and aperture information stored in the Canon RAW (CR2) files.

Have a look at:
http://en.wikipedia.org/wiki/Chromatic_aberration

With quote 1 in mind I wonder if it would be better to set the camera to spot focus, centre weighted metering and focus on the blue petals of the flower. i.e. force the camera to bring the blue plane in to focus.

I now must go and find some crocuses.

Theo

[Tracey McGovern]

Hi John / Theo

Thank you for your comments, they were very useful.

Theo - I keep forgetting I have DPP, automatically going streight into Bridge and Photoshop, which is bad really, as the software is designed specifically for Canon so I should start to use it more and will try to get into the habit of doing so. I have reworked the crocus to get rid ot the fringing, it worked a treat and was quite easy to do, the only thing is it washed out the colours a bit, they didn't appear as vibrant as they did in the original so I've had to boost up the vibrancy a bit to get it back to the original colours, but all in all, a success - thank you.

I don't think you'll find many crocuses left, most of them had withered away yesterday, there were just a couple still in full bloom.

Here is my re-work.

IMG_1022-web-v2.jpg (109.39 KiB) Viewed 5810 times

See you soon.

Tracey

[Paul Jones]

IMG_1022-web-v2.jpg

Hi Tracey

Not a comment on fringing, but just to say that you should consider cloning out the two white spots that leapt out at me when I looked at the photo.

There's a bright white spot towards the lower left hand side of the frame and another one above the flower in the 10 o'clock position.

Best regards
Paul

[Tracey McGovern]

Hi Paul

Yes I agree with your comments entirely, I'll give this image a full edit now that I have tackled the fringing problem.

Tracey

[oakeycoke]

Hi,

Mentioned it loads of times on here, but as Theo says DPP or a quick quote from Ephotozines write -up:

Digital Lens Optimizer – new in Digital Photo Professional v3.11
The EOS 5D Mark III comes complete with the most advanced version of Digital Photo Professional (DPP) yet – Canon’s free, in-box software enabling high-speed, high quality processing of RAW images. New in DPP v3.11 is Digital Lens Optimizer – a revolutionary new tool designed to drastically improve image resolution.

Digital Lens Optimizer (DLO) precisely imitates lens performance, with a series of complex mathematical functions replicating each stage of the journey of light through the optical path. Using this information DLO can correct a range of typical optical aberrations and loss of resolution caused by a camera’s low pass filter, by applying an inverse function to each shot to take the image nearer to how the scene appears to the naked eye. This creates exceptionally detailed, high-quality images with highly manageable file sizes, providing photographers with maximum image quality and greater flexibility.

Once you have loaded DPP on your computer any new updates are free, so no doubt this one will be along shortly, but i haven't checked yet. It's where Canon still manages to succeed over the other manufacturers in including useful processing software that is free. From memory you can load around 20 Canon lenses into the program and the click of a mouse will remove barrel distortion, chromatic aberration, vignetting and loads of other stuff.

The 18-200mm lens whilst being a good walk-about lens that's light(in weight not f/stop) and covers a large focal length, it does tend to suffer as John points out and Photozone says:

The level of lateral CAs (color shadows at harsh contrast transitions) is just acceptable for such a lens although the problem is very significant in absolute terms. At 18mm and 100mm the LCAs can exceed 2px on the average at the image borders and it's not much better elsewhere. The problem is clearly field relevant (although correctable to some degree via image post-processing).

The meta data, looks to be from Photoshop (bridge), but the focal length is missing, no doubt further down the list and probably well over 100mm, so putting you well into chromatic aberration territory.

A nice 100mm macro would have gone down well there.

Phil.