Sunday, 8 January 2012

Exercise 13: Managing Colour

Find two or three images that have a significant colour cast as the main purpose of the exercise is to ‘correct’ it.  Make sure that at least one image contains a surface that is ‘known’ (that is, expected) to be grey.  Among such grey surfaces are concrete, steel, aluminium, car tyres, asphalt, thick clouds and shadows on white.   First examine the image and make a judgement on the colour cast.  Then use your processing software to adjust both images to a satisfactory state.


JPEG

Here’s my original image with one with a purple cast from using Fluorescent white balance.


Image with Auto in camera white balance

Image with Fluorescent white balance


JPEG Procedures

This café image has a very distinctive purple colour cast so I needed to remove it by firstly using the grey point in Levels, see below:



Even with this the picture still has a distinctive purple cast so I opened up the Colour Balance palette and adjusted the three sliders to eliminate it as much as possible.  The new readings were:

Cyan/Red -6, Magenta/Green +4, Yellow/Blue +15


I think it would be virtually impossible to remove the colour cast from the notices in the window but I used the Magnetic Selection tool to selection just the notices and used the Colour Balance palette to make additional changes.


The additional changes I made were:

Cyan/Red -30, Magenta/Green +47, Yellow/Blue -30

These do seem to have restored the notices to a more natural colour as you can see from the Closed notice which should have been white but still retains the purple cast.


Here’s the before and after pictures to compare:

Before
After
---------------------------------------------
RAW

This is the image again with the Auto white balance as a point of reference

Original image
The original image in RAW which you can see below through the RAW Plugin converter:


You can see that there is a large amount of red in the picture, indicating that there is very little detail in those areas.  See screenshot below to see background details in the image:



I used the sliders to alter the image and remove the purple cast in the following amounts:

Recovery 25, Blacks 2, Brightness +47, Contrast +19

And the image changed to a more balanced colour way:


Final RAW converted image:


Using the RAW settings enabled me to get a more realistic image than from the JPEG image and having to work on it after I had opened it.  The RAW image stored information which could be changed more easily and successfully.





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