Notes on using the photo booth mode in DSLR Remote Pro, PSRemote, Webcam Photobooth and NKRemote

Part 7: Greenscreen Shooting

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Introduction

Green screen shooting (aka chromakeying) is the technique of shooting a subject in front of a green background and automatically replacing the background with a background image. Green screen shooting is used for movie special effects and for TV e.g. weather forecasts where the presenter stands in front of a computer generated weather map. It is available for stills photobooth shooting with DSLR Remote Pro for Windows, NKRemote, PSRemote and Webcam Photobooth. The live view images shown to the user are also green screened allowing users to interact with the virtual background and see what the final photos will look like. An optional foreground overlay image can also be used with transparent or semi-transparent areas. The users will appear behind the foreground overaly and in front of the background image. Different green screen backgrounds can be used for each shot in the photo booth shooting sequence - this is great fun at kids parties!

DSLR Remote Pro for Windows, NKRemote, PSRemote and Webcam Photobooth all support green screen shooting in stills photo booth mode and no additional software is required. You will also need a green background and suitable lighting. Green backgrounds and background supports are available from professional photographic suppliers and online stores such as Amazon.

Tungsten or fluorescent continous lighting is recommended for green screen shooting as this is easier to setup than flash. Flash is harder to use because it is difficult to get the right lighting for both the live view images, which don't use flash, and the actual photos which do use flash. The green background should be placed as far behind the subjects as possible to avoid problems with shadows being cast on the background as these may cause problems with the green screen removal. The green background should be evenly lit to give the best results.

Creating the backgrounds and selecting green screen shooting

The green screen background image can be any suitable JPEG image and should be placed in the photobooth images folder. For best results the background and overlay images should be the same aspect ration as the photos being taken by the camera otherwise they may appear stretched or squashed. The aspect ratio of photos from Canon and Nikon DSLRs is 3:2 (e.g. 1500 x 1000 pixels). Photos from Canon PowerShot cameras have an aspect ratio of 4:3 (e.g. 400x300 pixels). The aspect ratio of photos from a webcam will depend on the webcam being used and the resolution setting.
The background and overlay images only need to be big enough to look good in the live view display and to print well e.g. if you want to offer 6" x 4" reprints @ 300 dpi of single photos the green screen background needs to be at least 1800 x 1200 pixels in size. You can make the background and overlay images larger, but this may cause a slightly longer delay when the photo booth software loads and resizes them.

The background image should be named greenscreen_background.jpg and saved in the photobooth images folder. An optional foreground overlay image can be used by creating a PNG image and saving it as a file named greenscreen_overlay.png in the photobooth images folder. The PNG overlay image should be a 24-bit color image with transparency information in the alpha channel. Different backgrounds and foreground overlays can be used for each shot in the shooting sequence by saving additional images in the photobooth images folder and naming them greenscreen_background_2.jpg, greenscreen_background_3.jpg etc.

Once the foregrounds and backgrounds have been created green screen shooting can be enabled by selecting fullscreen photobooth mode and typing Ctrl+G to display the green screen setup dialog:

liveview_greenscreen_settings

First click on the checkbox to enable green screen display and then adjust the sliders so that all of the green screen background is replaced with the background image but the foreground subject is unaffected. The easiest way to do this is to move the "Green threshold" slider to the left until most of the background is replaced and then fine tune the settings by moving the "Red level" and "Blue level" sliders to the right. The best settings to use will depend on the lighting conditions and the quality of the green background. If areas of the subject show the background the settings are too strong and should be reduced by moving the red and blue sliders to the left of the green slider to the right. Select the "Blue screen mode" to use a blue background instead of a green one.

Select the "Save copy of greenscreened photos in photo booth mode" option to save a green screened copy of the individual photos taken by the camera. These are stored with the original photos from the camera in a subfolder named "Greenscreen".

Switching Backgrounds

Users can be given a choice of backgrounds by saving each set of backgrounds in a different photobooth images folder and then use the profiles feature to switch between them. For example suppose you have backgrounds from major cities around the world and would like to let the user choose which set to use you could create separate photobooth image folders for each city and name them something like London, Paris and New York. Next copy the green screen background images, screen images etc. into each folder. Then edit the photobooth settings to use the first photobooth folder, London, and save the settings as London.xml. Repeat the process by setting the photobooth images folder to Paris and save the settings as Paris.xml and finally set the folder to New York and save the settings as New York.xml. Next click on the "Profiles..." button and assign profile 1 to London.xml, profile 2 to Paris.xml and profile 3 to New York.xml. The profiles dialog should look something like this:

The ready.jpg screens in each of the folders should be edited to show which green screen background has been selected. Then when the photobooth is running the user can select London by typing Shift+Ctrl+1, Paris by typing Shift+Ctrl+2 or New York by typing Shift+Ctrl+3. If you are using external buttons and a StealthSwitch II to control the booth you could program dedicated buttons to select each profile. Alternatively you could use a touchscreen and define touchscreen areas to select each profile.

An alternative way of switching green screen backgrounds is to copy the new greenscreen_background.jpg image (and optional greenscreen_overlay.png image) into the photo booth images folder. The photo booth software will detect that the background image has changed and will update the display automatically. The two AutoHotKey scripts described below provide different ways to select green screen backgrounds using a numeric keypad.

photobooth_greenscreen_backgrounds.ahk - a script to select from 14 backgrounds using a numeric keypad
This script is designed to be used with an external numeric kaypad and allows the + and - keys to switch to the next or previous background and the other keys to load up to 14 different backgrounds directly. To use the script simply name the various backgrounds gs1.jpg, gs2.jpg, gs3.jpg etc. and copy them into the photobooth images folder. Corresponding overlay files, if required, should be named gs1.png, gs2.png, gs3.png etc. Run the script by double clicking on it using Windows Explorer. Then press the keys on the keyboards numeric keypad (or use a separate numeric keypad connected to the computer) to select the 14 different backgrounds or press + or - to step through them.

photobooth_greenscreen_backgrounds_by_id.ahk - a script to select from up to 1000 backgrounds by entering a 3-digit id using a numeric keypad
This script allows a three digit numeric code to be entered to select from up to 1000 different green screen backgrounds. To use the script simply name the various backgrounds gs001.jpg, gs002.jpg, gs003.jpg etc. and copy them into the photobooth images folder. Corresponding overlay files, if required, should be named gs001.png, gs002.png, gs003.png etc. Run the script by double clicking on it using Windows Explorer. Then enter the three digit id using the numeric keypad. Pressing a non-digit key (e.g. /, *, -, +, Enter) will clear the id and allow a new one to be entered.

Download the photobooth_greenscreen_backgrounds.ahk and photobooth_greenscreen_backgrounds_by_id.ahk scripts: photobooth_greenscreen_backgrounds.zip

Using profiles to select from more than 8 backgrounds

The photo booth software only allows up to 8 profiles at a time to be defined but this doesn't limit the number of profiles that can be used. By using the {photoboothDir} token to specify the profiles each photo booth images folder can have its own set of 8 profiles. If each profile selects a different photo booth images folder it allows another 8 profiles to be used.

For example suppose you want to offer the user the choice of 14 different green screen backgrounds this can be done be defining two pages of 7 profiles with a touchscreen action to switch between the two. First create 14 photo booth image folders to hold the different backgrounds and name them folder1, folder2, folder3 etc. Then save 7 sets of settings in folder1 and name them as follows:
profile1.xml - this switches to folder8 to display the next screen of 7 images
profile2.xml - this switches to folder1 to select green screen background 1
profile3.xml - this switches to folder2 to select green screen background 2
profile4.xml - this switches to folder3 to select green screen background 3
profile5.xml - this switches to folder4 to select green screen background 4
profile6.xml - this switches to folder5 to select green screen background 5
profile7.xml - this switches to folder6 to select green screen background 6
profile8.xml - this switches to folder7 to select green screen background 7

These settings files can then be copied to folders folder2 to folder7.

Next save another 7 sets of settings in folder8 and name them as follows:
profile1.xml - this switches to folder1 to display the previous screen of 7 images
profile2.xml - this switches to folder8 to select green screen background 8
profile3.xml - this switches to folder9 to select green screen background 9
profile4.xml - this switches to folder10 to select green screen background 10
profile5.xml - this switches to folder11 to select green screen background 11
profile6.xml - this switches to folder12 to select green screen background 12
profile7.xml - this switches to folder13 to select green screen background 13
profile8.xml - this switches to folder14 to select green screen background 14

These settings files can then be copied to folders folder9 to folder14.

Then define profiles using the {photoboothDir} token as shown below:

All the photo booth image folders can contain exactly the same screens etc. but will have different greenscreen_background.jpg images. You could then create two ready.jpg screens: one to be saved in folder1 to folder8 showing thumbnails for backgrounds 1 to 7 and a button for the next page and the other to be saved in folder8 to folder14 showing thumbnails for backgrounds 8 to 14 with a button for the previous page. A highlight could be added to the currently selected background by editing the ready.jpg screen in each folder to make it easier for the user to navigate through the various screens.

An example of how to use profiles to select from 16 green screen backgrounds using DSLR Remote Pro for Windows and a 1920x1080 touchscreen can be downloaded from: gs_bg_example.zip
Please see the ReadMe.txt files for usage instructions. Please note that this example is slightly more elaborate to the one described above as it allows up to 8 backgrounds to be selected from each page.

Next article: "HowTo's" and Frequently asked questions
Previous article: Other aspects such as reprints, captioning, running a slideshow and customization


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Using photo booth mode in DSLR Remote Pro for Windows, DSLR Remote Pro for Mac, PSRemote, Webcam Photobooth and NKRemote