Pre-planning considerations may include: (1) knowing that you are going to change the background; (2) that the background is static during the time it takes to make both 'shots'; (3) that the main subject backgound shadows are not of major importance; (4) remembering to switch camera 'auto' settings to manual after taking the combined main subject/backgound shot so that the camera maintains exposure, focus, and aperature for the background shot; (5) and of course, all this accomplished using a steady tripod.The next time you have a project where you know in advance you are going to replace the background behind the subjects, try this.
Shoot two shots on a tripod. One with the subjects and one with the background only.
In post processing follow these steps:
Layer the background only image over the image with the background and the subjects.
Set the background image only layer (top layer) to difference mode.
Stamp Visible.
Use magic wand (with tolerance set to 2, contiguous off) to click on the Black background.
Type Q to enter Quick Mask to check selection and clean up any bits that should not be part of the selection. (Type Q again to leave Quick Mask Mode)
Duplicate the original image (with the subjects and background) and place on the top layer.
Inverse the Selection.
Add mask to the image layer.
Place new background image under this layer.
Try this procedure with these images. (download from: http://forums.dpreview.com/forums/read. ... e=35300586 ..den)
If you are really, really bored, try extracting the pineapple with your favorite masking program / method.
Let me know if you have any questions.
This is a great technique if you are shooting group shots at a wedding outside and the background is not so great. A little planning will save you lots of time in post.
Mike
A PWP5 suggested main subject mask workflow...
(1) download the OP's 'backgound_only' and 'pineapple-bkg' jpegs.
(2) click on the 'pineapple-bkg' image, open Composite-AbsoluteDifference, set Overlay = the 'background_only' image, click OK.
Creates an 'AbsoluteDifference' image where the background image areas are black with some isolated black in the main subject image areas.
(3) click on the resulting (2) image, open Mask Tool - BrightnessCurve, form, 'lower-left' Apply Add, OK a BrokenLine curve = [0,0], [10,100], [100,100].
Masks the backgound image areas surrounding the main subject with a slight outline edge gradient.
(4) click on the resulting (3) mask image, open the Mask Tool - BrightnessCurve; form and 'lower-left' Apply Add the default [0,0], [100,100] diagonal curve; and then form, 'lower-left' Apply Subtract, OK a BrokenLine curve [0,100], [50,100], [100,0].
Subtracts the black [0%] to 50% toned outline edge gradient from the mask.
(5) click on the resulting (4) mask image, open the Mask Tool - FloodFill; select large background areas [black] as needed to isolate the main subject [white with gray mix]; Invert; OK.
Eliminates the main subject non-white mask image areas inside its outline.
The resulting (5) mask image is sharp edged and will require further preferential feathering and/or blur when used to Composite-Blend the main subject with its new background...
(3), (4), and (5) resulting mask images should look something like this, left to right:
- masks 3,4, and 5_400px.jpg (27.43 KiB) Viewed 7182 times
- ori-new_backgnd_400px.jpg (47.6 KiB) Viewed 7182 times