Wednesday, May 26, 2010

Tutorial - Extracting Image with Blurred Edges and Replacing Background

This article describes how to extract objects that have some movement on the edges and then replace background and not have the image appear as a cutout and placed on a new background.

The main feature is selecting the outline of the ducks with magic wand and then applying a white colour stroke to create a 10 pixel outline. This will be used later to re-introduce some blur around the duck wings to make this more realistic and not quite the cut-out effect.

The black winter pool cover was still on in the backyard pool and with some recent rain, two Mallard ducks thought this was an interesting place to visit and feed on some of the algae growing in the warm stagnant water.

There is a cedar hedge all around the yard so with this privacy, they have landed many times over the years. This always gives me a great opportunity to step out and photograph at close range.  They are not too afraid and normally I can get to within 15 feet of them. The problem is actually getting them to fly away for those interesting winged shots without scarring them so much that they won't come back.

I noticed that the male duck would bob its head up and down as I would approach.  I mimicked this bobbing motion and within a few moments this caused them to fly away.

A soft sky background would make the Mallards stand out nicely. Just having installed Photoshop CS5, I thought this would be a good opportunity to try the new refined edge when creating masks.
I will explain my approach by using the layers' palette, as the discussion's focal point, going from the bottom to top.

In the panel below (number 1-6 going left-right and top – bottom ) the image top right (#1) is the original capture as they flew away from the pool. The ducks are reasonably crisp but there is way too much clutter around and the female duck is almost hidden in the tree branches.

Original Duck Image – the original image captured by camera is in panel #1

Sky background
– suitable sky selected from files panel #4. It was flipped horizontally so that the diagonal of cloud sky edge matched the linear motion of ducks going from bottom right to top left.

DSC6177 Smart RAW copy for color extraction
– Copy of RAW file inserted as a smart layer. This version allowed me to darken the sky (more blue – panel #2) to help with refine edge to better detect change between white feathers and sky. Once mask refined, it was saved as a channel for each of the ducks

Mask for larger Duck -  The channel mask for large duck loaded and applied to copy of original duck image.

Mask for small Duck – The channel mask for small duck loaded and applied to copy of original duck image.

Mid Gre
y – A mid tone grey fill layer created to assist with viewing and refining edges against background. Some of the bird edges are white and with an almost white sky it is harder to detect edge.
Whenever using automated tools, I find it's always better to assist with the task by either changing contrast or colours to make the extract easier. Here I used colour changes in RAW files. Sometimes I may even go to over-saturation when dealing with earth tones.

Merge Ducks Master
  -  both masked images for ducks loaded as a new layer. See panel #3 but with no grey background.

Stroke Mask for edge of Ducks -  The Merge Ducks Master Copy and Mid grey selected and magic wand used on grey background. This gives me a marching ants selection around ducks. This section was then stroked (Edit-Stroke with a 10 pixel, white, center) setting creating panel #5.

B&W Luminosity – a Copy of Merge Ducks Master copied and set to luminosity mode.
B&W Adjustment color effect - A  B&W adjustment layer was applied to this B&W Luminosity layer and adjusted for desired colour effects. The Blue, cyan and yellow  increased to lighten colour. See panel #8.

High Pass
- Copy of Merge Ducks Master and a high pass filter applied and layer set to overlay mode. See panel #7.

Blurred Winged Edges – Original layer copied and Gaussian blur applied (3.5px). The Stroke Mask for edge of Ducks was applied as a mask and the main body duck edges were painted black with 50% opacity to reduce blur effect on these parts but have the most blur on the moving wings. Panel /6 is mask.

This stroke mask could also be used to reduce colour fringing around the edges by applying a Hue/Sat adjustment layer and reducing saturation of problem colour. The mask keeps the effect to just the edges and a smaller stroke pixel setting can be used to limit the width of colour changes.  Normally for photographers, the desired change is to replace skies. With desaturation, the greying will match tones of non blue skies. If blue sky is desired then use the Hue/Sat layer but instead shift the hue of the problem fringe colour.

This is a closeup of the male Mallard duck sitting in the swimming pool with some water on the black winter pool cover.

Niels Henriksen

1 comment:

Denver Photographer said...

nice tutorial. I think the high pass filter is definately a good use for extracting parts of an image like that.


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