PP Tips 14 - Removing Chromatic Aberration

This is part of a 'How To' series on post process work.

Many of today's cameras have routines 'built-in' to remove lens aberrations. This includes lens distortion correction and also chromatic aberration (CA). Typically, these are very effective routines.

A large majority of lenses will display CA. Certainly most of the lenses I have owned over the years have displayed CA, in differing severity, from the very cheap to the very expensive.

Most good image editors have CA correction routines. Some work well, some not so well.

The ones I will cover here are Photoshop, DxO Optics Pro, and also an action for use in Photoshop.

Firstly, what is CA ?

If you want a detailed technical explanation, I'm the wrong guy to ask. I'm not that smart. However, good news, have a look at this link for an explanation at Cambridge In Colour - Click here

More simply, and so we can see it's effects in an image, here is an example of an image with CA, at left, and after it is fixed, at right.

This is a 100% view of the image and is only showing the very top right hand corner.

Note : Clicking on any image will take you to a larger example of that image

As can be seen in the example above, the Chromatic Aberration manifests itself in the form of purple fringing (PF), but also with green fringing.

So, let's explore a few ways to reduce/remove the CA.


Example 1

The original image.

Example 2

Fixing the image using the PF Killer action in Photoshop.

Note : This is a simple action which you can download - Click here. It is the action at the bottom of the page. The original web site for this has disappeared

Once downloaded, simply copy it to the Presets/Actions folder for Photoshop. When Photoshop is opened, just load the action for use.

Here I am simply showing the before/after as if you are familiar with running actions in Photoshop, it will be intuitive.

As can be seen in the above example, PF Killer does a good job of removing the purple CA. However, it does not tackle the green fringing.



Example 3

Note : I open all my Raw and Jpeg images in Adobe Camera Raw (ACR). To understand how to set up Photoshop/Photoshop Elements to do this - Click here

Here, I have opened my image in ACR and selected the Lens Corrections pane. This is also pretty much the same as the adjustments which are available in Adobe Lightroom.

Example 4

As there is no preset profile for my camera/lens combination in ACR, I have selected the Manual tab. If your camera/lens combination does have an Adobe profile, then it should correct automatically.

With the Manual pane open, I have selected Defringe : All Edges, and adjusted the Red/Cyan Fringe and Blue/Yellow Fringe sliders.

For this particular image, I have used the values of -20 and +50 respectively. This will be different for any given camera/lens combination.

Example 5

The original image, at left, and the image after adjustment in ACR, at right.

Example 6

As can be seen, in the above example, ACR has done a good job of reducing the CA but has not removed it all, especially the purple CA. One way to help remove this, is to now run the PF Killer action.

Here, are the same images shown in the last example but with PF Killer now run on the image at right, and after the adjustments I made in ACR.

Example 7

If your camera/lens combination has a Lens Correction Module in DxO Optics Pro, then I have found this to be pretty much the best CA correction tool I have used.

Note : To check if your camera/lens combination is supported with a DxO Lens Correction Module - Click here to check DxO's availability page

The image as opened in DxO.

Example 8

In this case, my camera has a Lens Correction Module in DxO.

Here, DxO has automatically corrected the image. In the 'Detail' pane I have turned off the 'DxO Lens Softness' correction and turned on the 'Purple Fringing' correction.

Simple.

Note : I also have DxO Lighting HDR Slight - Auto turned on. Hence the lighter image

Examples 9 through 13

These examples simply show the effects, on an image which has a predominance of purple and blue, and the effect which different CA removal techniques have on those colours. The image has purple fringing in the top left corner which I wish to remove.

The original image.

Note : Clicking on any image will take you through to a larger size

Fixed in ACR - Manual process as there is no lens correction profile for this camera/lens.

Fixed in DxO - Automatic.

Fixed with PF Killer. As can be seen, this is one of the draw backs with PFK. It is non-discriminate.

The same image as above, but what I have done here is to 'unlink' the correction mask layer and then use the Magic Eraser to restore the colours in the fishermans clothing. Again, a manual process.

Anyway, That's it. Hope you find it helpful.

Cheers

Other posts in this series - Click here for the index page.


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Post Processing Tips Index

Want to join a photography centric forum ? To join the EyeMindSoul Photography forum, click here

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This page simply serves as an index to a collection of tips about post processing. There is a link at the bottom of each post which will bring you back to this index page.

It is divided into two sections. The first section deals with tips which are Photoshop specific, the second with tips for stand alone programs.

Section One - Photoshop/Lightroom

1. Preserving Highlights - Click here

• How to use the Color Range tool to inversely select, and preserve highlight areas, whilst doing any post process work in Photoshop.

2. Not Using Layers - Click here

• This is about ways to do post process work in Photoshop, without using 'layers' yet still have control over the intensity of some of the straight forward adjustments.

4. Simple Sharpener - Click here

• Using a purpose written Photoshop action to sharpen an image.

5. 'Pop' - Click here

• Adding 'pop' to an image. A simple way to enhance the colour of an image without accentuating noise.

6. Using Layers - Click here

• This post is Photoshop specific, and it is only a basic, and very simple, explanation about layers, and how/when to use them.

7. Editing Jpeg's In Raw - Click here

• How to setup Photoshop so that you can use the editing functions found in Adobe Camera Raw (ACR) to edit Jpeg images also.

8. Straighten Up - Click here

• Two techniques, in Photoshop, which can be used to straighten the horizon.

9. Bag That - Click here

• Using the Patch Tool to remove 'bags' under eyes.

11. 'Pop' Too - Click here

• This is an alternative method for giving an image a little colour lift, in Photoshop, and without introducing noise.

13. Resizing An Image - Up - Click here

• Simple overview of resizing (upsizing) an image in Photoshop.

14. Removing Chromatic Aberration (Photoshop and DxO) - Click here

• Removing CA using Photoshop Adobe Camera Raw, or using DxO Optics Pro. Also using a purple fringe (PF) removing action for Photoshop.

17. Paint It Black - Click here

• Using the Vivid Light brush tool to lighten, darken, or add localised contrast to an image.

21. Using A Provia Curve And Sharpening Action - Click here

• A Photoshop action which applies Provia film simulation and sharpening.

23. Simple Photoshop Black And White Technique - Click here

• A technique for converting colour images to black and white.

24. Using Masks In Photoshop - Click here

• Some different techniques for creating 'nasks' and using eit tools with them.

25. Using Adobe Lightroom - Click here

• A simple overview of using some of the adjustment tools in Adobe Lightroom.

Section Two - Stand Alone Programs

3. Using Windows Live Photo Gallery - Click here

• Using WLPG for editing/adjusting an image

10. Using The (supplied) Raw File Converter For The Fujifilm HS-10 - Click here

• This post links to several pages on one of my other sites (PixPlanet) and shows several examples of using the RFC to edit Raw and Jpeg files from the Fujifilm HS-10

12. DxO Optics Pro 6.5 - Click here

• Some screen shots, and edit examples, showing some of the different things you can use DxO for.

15. HDR Express - Click here

• This is a stand alone program which can be used to create single, or multi shot HDR images.

16. Virtual Photographer - Click here

• An effects program (plug in) which can be used in Photoshop, and other editors, and also in Virtual Studio which is a free editor and plug-in handler.

18. Editing With SilkyPix DS Pro - Click here

• A PDF document is available for download. This gives a brief overview of some of my normal work flow process.

19. Editing With FastStone - Click here

• A PDF document is available for download. This gives a brief overview of some of the edit functions available in FastStone.

20. Using the FujiFilm RFC EX Raw File Converter - Click here

• A PDF document is available for download. This gives a brief overview of some of the edit functions available in the FujiFilm RFC EX.

22. Using the FujiFilm RFC EX Raw File Converter With HS-10 Raw Files - Click here

• How to change HS-10 Raw Exif information so the RFC EX can process it.

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Additional Tips on my PixPlanet site :

Other (older) Post Processing tips. I will update these, and bring them across to the blog, over time.

Click here for the index page.

Topics covered :

• Using High Pass to enhance an image.
• Another example of the above technique plus information for resizing and saving images.
• Using specific tool for localised repair or enhancement.
• Using Unsharp Mask (USM) to add contrast to an image.
• Converting a colour image to black and white.
• Creating an 'Orton' effect
• Getting more 'pop' from colours - Technique 1
• Getting more 'pop' from colours - Technique2
• Toning a black and white image.

Cheers



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PP Tips 13 - Resizing An Image - Up

This is part of a 'How To' series on post process work.

This is Photoshop specific, but most good editors work in a similar manner.

Note - You really need pay attention here as there are many complicated steps  !?!? Joking

Here, I am (re)sizing an image from it's base 9.6 x 12.8 inches size, to 30 x 40 inches. In other words, I am sizing it 'up', and a long way up at that.

It is not that I would print this particular image at that size, but I chose it as an illustrative example as it is clear and sharp.

Note : This is about sizing 'up', not about cropping. I will cover that in another topic

First things first. Do any editing work first. If your monitor resolution is setup correctly, for Photoshop, then if you view the image at 100% for, say, a 9.6 x 12.8 inch print such as mine, you will be viewing it as if it would print at 30 x 40 inches

With the base image I am using, it is 3840 pixels (picture elements) by 2880 pixels. My 23 inch monitor resolution is 96 (95.78) pixels per inch (PPI) and if I divide the image pixels by 96, I get 30 x 40 inches. 3840/96 = 40, 2880/96 = 30.

Similarly, if viewed at 50%, it is as if it would print at 15 x 20 inches. If it looks poor at 50%, or at 100%, it will also look poor printed at these large sizes.

To calculate your own monitor PPI, click here for a simple, but very effective, calculator.


As an example, my own monitor calculation.

Knowing that the monitor PPI is 96, in Photoshop I click Edit/Preferences/Units & Rulers and enter my monitor PPI in the Screen Resolution box.

Note : Use the calculator as it will give you an accurate number based on all your screen criteria. Photoshop's default value is 72 PPI

OK. Here is my base image. Nothing exciting, but it is clear and sharp. Besides, I couldn't afford a professional model.

Note : Clicking on any image will take you to a larger size of that image. Detail is a little hard to see at the sizes displayed here

So, how would I resize this image from 9.6 x 12.8 inches to 30 x 40 inches ?

It's very simple. I select Image/Image Size and enter my new values. I make sure the Resolution is still 300 pixels/inch, Constrain Proportions is checked and I use Resample Image : Bicubic Smoother.

You think I'm joking ? Well, actually I'm not. I do this in practice all the time.

However, let's dig a little deeper.

First, let's look at the detail in my original 9.6 x 12.8 inch image, and if viewed at 100% (30 x 40 inch print equivalent).

Second, let's look at the detail in the image, after resizing to 30 x 40 inches, and if viewed at it's new actual print size.

See the difference ?

Let's look a little closer.

At left, my new resized image shown at print size. At right, the original viewed at 100%.

If you read some articles, you will find many different opinions on how to resize an image. Some have merit, some are rubbish. I'm being polite.

I am not saying that the way I describe is the only way, nor is it the absolute best way, but it works for me and most of my associates do the exact same.

I run a gallery and print anywhere between 8 x 11 inches to 30 x 40 inches. My typical largest size is 23 x 32 inches, and 30 x 40 inch is an occasional size. However, the principles are the same for upsizing for any size larger than the base image size.


Anyway, let's look a little further at some different options in Photoshop.

Example 1
One oft touted method is to upsize the image in incremental steps. In other words, upsize the base image a little, then upsize the result, and repeat, etc., etc.

In fact, I used to do this religiously, until one day I really had to ask myself - Why ?

For the example I show here, I used 'Bicubic Smoother' and incremented in the following steps :

Base - 9.6 x 12.8 inches
Step 1 - 12 x 16 inches
Step 2 - 16 x 21.333 inches
Step 3 - 22 x 29.333
Step 4 - 30 x 40 inches

You can use many more 'steps' but, in reality, it achieves little, if any more than the steps I have shown.

At left is detail of the image which I simply upsized to 30 x 40 inches. At right, the 'stepped' image.

Note : The right hand image is flipped horizontally for comparison purposes

Example 2
The same as the above, but this time I have simply used 'Bicubic', as opposed to 'Bicubic Smoother', for my image resampling.

Example 3
Again, the same except that I have used 'Bicubic Sharper' for my image resampling.

Anyway, That's it. Hope you find it helpful.

Note : After resizing, at times I will add a little more sharpening. It is purely image dependent. Remember that with today's monitors, the image will appear sharper on screen than when it is actually printed


Cheers

Other posts in this series - Click here for the index page.


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Fujifilm S100 fs - Resetting

I've had my Fujifilm S100 fs for over two and a half years and shot close to 32,000 images with it.

Mostly I shoot Raw, or if shooting Jpeg I prefer to use Astia film simulation.

I wanted to increase the in-camera sharpening but found that this causes it to revert back to Provia. As a little experiment, I decided to just shoot Provia with the Sharpness set to Hard and the Colour set to High.

So, for the past two weeks, this is how I have been shooting it.

The images below have been shot in Provia and with colour and sharpness set to high. They are simply shown in chronological order.

All passed through DxO Optics Pro to fix any lens anomalies, but are not otherwise edited. The exception is that a few of the night shots have had some chroma noise reduction and one was cropped.

With setting sharpness to high and looking at an image at 100% view (pixel peeping), sharpening artifacts are evident. However, at reasonable print sizes (say A3) they are not apparent.

The advantage of doing this ? It gives a clean and sharp image which can easily be simply edited to pull out the colour, if desired.

Enjoy.

From here on, the images were all shot this morning and with a very overcast and 'dirty' sky.

 

Cheers



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