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Introduction
In this tutorial I will show you how to delete an image background, resize your replacement backdrop in order to fit your original picture and paste your subject onto the resized replacement backdrop

I will use a photo of a woman with an outdoor background, but you can apply the techniques discussed in this tutorial to any photo, whether taken indoors, outdoors, with other people, etc.  The principles taught here remain the same for any picture; it is only the degree of difficulty that would vary.

The program used in this tutorial is GIMP 2.4.6, but you would be able to do the same with older versions of GIMP.

Useful tips and advice will be highlighted with an arrow →.

Step 1: Getting started

§     Open your original picture in GIMP.

§     Immediately ‘Save As’ your image with a new file name, to avoid saving changes by mistake to your original picture.  For our purposes, I will be saving my image as the ‘subject image’.

→      If you’re using GIMP, save it as a ‘.xcf’ file to avoid losing the quality of your picture. The same would apply to any other program that you might use.  Always save the image as the preferred file type for that specific program.  This will allow you to work in layers with transparent backgrounds, without losing any data due to compression.

Adjust the color & brightness of your image, if necessary.  A clear, bright image will display better against your replacement backdrop

Use ‘Layers’ and ‘Color’ menu for easy access during your tutorial.

→     GIMP Keyboard Shortcuts: Color Alt+C, Layers Alt+L

Step 2: Promote the background layer (if required)

§     Before continuing to edit the background of your image, ensure that you’ll have a transparent background (grey/ white checkerboard) and not a solid color when using the ‘Selection Tool’ or ‘Eraser’ to delete part of your picture. 

§     Look at the ‘Layers’ window.  (See Fig 2a)

§     If it says ‘Background’ next to your thumbnail picture, you’ll have to promote the background layer by following the guidelines below. 

→      Go to ‘Layer’ in the top menu bar; select ‘New Layer ’ and then select ‘Background Color ’ in the Layer fill type. (See Fig 2a) 

→      Most software provides a tool for this.  Search the ‘Help’ menu of your software for more information on creating Layers and Transparent layers. If it doesn’t support this action, continue with Step 3 and I will cover both scenarios as we go along, with or without working with a transparent background.

Step 3: Cut out excess parts of background

§     Cut out or erase the excess parts of your picture’s background that you don’t want in the final image. 

§     Use the ‘Selection Tool’ or ‘Lasso Tool’ to highlight parts of your photo and press the ‘Delete’ button on your keyboard to erase the selected area.  However, be careful not to select parts too close to your final image. (See Fig 3a)   

→      I recommend zooming in on different parts of your picture as you’re doing this, for greater accuracy and ease.

→      GIMP Keyboard Shortcuts: Zoom In  +, Zoom Out  -

→      If you have a solid color background after erasing parts of your picture, and you’re not working with transparent layers, don’t worry.  I will guide you in Step 7 on how to get the background transparent.

→      If you make a mistake, go to the ‘Edit’ menu and click ‘Undo’.

→      Remember to save your work continuously.

→      GIMP Keyboard Shortcuts: Save CTRL + S

Step 4: Use the eraser tool, zoomed in

§     Select the ‘Eraser Tool’ in your ‘Tools’ Palette.

§     Then zoom in to the areas that need to be deleted and carefully use the ‘Block’ mode eraser (Fig 4a) to delete these areas.  Don’t go to close to your final image though.

§     After deleting the bigger areas with the block eraser, select the ‘Brush’ mode eraser and choose the settings that would best suit your needs.  (See Fig 4b)

Fig 4a

→      Play around with the settings until you find what works best for the part of the picture you’re working on.  For example, for close up work, zoom in and use a smaller size eraser.  Or, for hair, select a light brush that is thinner and diagonal in shape, to get between the hairs that go out into the background.

§     Use an eraser setting with low opacity or low hardness to go over the edges of your images.  This will create the effect that your background is fading out, instead of your image being harshly cut out from its original background and pasted on a new backdrop.  

→      Getting the desired effect will take some practice.  I recommend taking it slow and playing around with the different eraser settings until you’re comfortable with the tool.  Zoom in and out of your picture from time to time to check the result at 100% zoom.

→      Remember to delete all areas that might show between the arms, legs, hair, etc.

Fig 4b

Step 5: Save your new image

§     ‘Save As’ your new image with the deleted background.  This will allow you to go back to this image and re-use it on different backdrops. 

§     For our purposes, I will be saving my image as the ‘subject image cut out 01’.

Step 6: Open your replacement backdrop and resize images

§     Keep your newly saved image, ‘subject image cut out 01’, open while opening the new backdrop file as well.

§     Both images should now be side by side on your screen.  (See Fig 6a)

§     Ensure that both images have similar resolution and dimensions (either pixels or inches).   This will assist you to bring the two images together without having either a too small or too large backdrop.

→      Always make your larger image smaller, as you can size down images and still preserve image quality.  However, you cannot make smaller images larger without losing quality. 

§     Look at the image information of your ‘Backdrop image’ photo.  It should display similar information as Fig 6b.

→      Most software has a menu choice such as ‘Image Information’, ‘Image Details’ or ‘Properties’. 

→      In GIMP: Go to ‘Image’ in the top menu bar; and select ‘Image Size’, Keyboard Shortcut Shift +T. (See Fig 6b)

 Ensure that you’re on the correct image before getting its information.  You can switch between your open images by clicking on its title bars

Fig 6b

§     My subject image’s size, including the clear background, is 454 x 300 pixels; and the resolution 72 pixels per inch.  Record your subject image’s properties to compare it to the new backdrop’s size and resolution.

§     Click on your new backdrop image title bar in order to view and if necessary, adjust its proper ties.

→      In GIMP: Go to ‘Image’ in the top menu bar; and select ‘Image Size’, Keyboard Shortcut Shift +T.

§     My new backdrop image’s size is 800 x 600 pixels; and the resolution 150 pixels per inch.

§     For my purposes I need to adjust the resolution of my new backdrop image to 72 pixels per inch.  This will change the pixel dimensions to 454 x 300 pixels. 

§     I then adjust the pixel dimension of my subject image to 454 x 300, keeping the ‘aspect ratio’ locked.

§     You will notice that the new width of my subject image is slightly wider than the backdrop image.  That doesn’t matter, as the subject image has plenty of transparent background on the left. 

→      Important: 

-          Compare inches to inches or pixels to pixels.

-          If your images have different resolutions and sizes, always adjust the resolution first and then the sizes.

-          Ensure that, when adjusting the size of your image(s), the ‘aspect ratio’ is locked.  When you therefore type in a new width, the height will automatically be calculated based on the original size of the image.  Maintaining the original ‘aspect ratio’ of your image will avoid picture distortion when resized.

→      Resizing images can be quite tricky.   If you’re not happy with the changes you have made, remember that you can ‘Undo’ at any time.  Experiment until you get it right.  However, be careful not to resize your subject image too small, with a low resolution, or your prints will be lower quality than the original.

Step 7: Prepare the subject image to move to the backdrop

(This step is only for those who have a solid background on their subject image, after erasing the background.)

§     Keep both your images open after completing Step 6.  It should look like Fig 7a.

Fig 7a

§     Click on your new backdrop image tool bar and create a new layer that would be above your background layer, or first layer.

→      In GIMP: Go to ‘Layer’ in the top menu bar; select ‘New’; and then ‘Layer’ again.  Keyboard Shortcut SHIFT + CTRL + N. 

§     Go to your subject image and select the ‘Magic Wand Tool’ and click on the solid background color, which is white in my example.

§     If there are any other solid background areas not selected, hold down the SHIFT key while clicking on that areas too. 

§     You may notice that your selection is cutting some of the subject image.  Don’t worry if this happens.  You can correct it during the next few actions.

→      Holding down the SHIFT key should work with most software.  If it doesn’t work, search your software’s Help menu on how to highlight multiple areas at once.

→      You can also adjust the tolerance settings of your ‘Magic Wand Tool’ and experiment how it affects what the tool selects/ highlights.  (See Fig 7b)  Also make sure that the ‘Anti-alias’ option is selected.  You’ll need to get the selection tight on your subject image, leaving no background outside the lines of the highlight.  I suggest setting the tolerance level quite high, even if some of your subject image’s hair or face is cut off.

§     Go to your menu options and ‘Invert’ the selection.  The subject image should now be selected instead of the background.

→      Go to ‘Select’ in the top menu bar; and select ‘Inverse’.  Keyboard Shortcut CTRL + I. 

→      If you didn’t set the tolerance setting of your ‘Magic Wand Tool’ high enough before the ‘Invert’ action, you might see that the selection, when you zoom in, includes too much background color.  The highlight should be as tight as possible, but not to include any solid background color.  If your selection of the subject image includes too much solid color, select ‘Undo’ until the background is selected again and adjust the ‘Magic Wand’ tolerance setting, and then try to invert your selection again. 

§     If some of your subject image is not included in your selection, hold in the SHIFT key, while still using the ‘Magic Wand Tool’ and select those areas that need to be included in the selection.  Or use any other selection tool that works for you. 

§     When you’re done with this step, your subject image should look like Fig 7b.

Step 8: Move the subject image to the backdrop

§     Ensure that both your subject image and backdrop image is open, as shown in Fig 6a.

§     Click on your subject image title bar and highlight the image by pressing CTRL + A on your keyboard; and then CTRL +C to copy the selection or select copy from the ‘Edit’ menu.

§     Click on your backdrop image title bar and press CRTL + V to paste the image onto your backdrop.

→      Go to ‘Edit’ in the top menu bar; select ‘Paste’.

→      Use the paste option that allows you to paste the selection into the backdrop image and not a new image altogether.

§     Reposition your subject image to where you want it to be on the backdrop image.

Your backdrop image should now look like Fig 8a.  If you are not happy with the proportions of the subject image and backdrop, select ‘Undo’ and resize your images accordingly until you get it right

Fig 8a

Step 9: Adding the final touches

§     Look over your final combined image and see if it looks natural. 

§     If too much of the original background is showing on the edge of the subject image, go back to the original ‘subject image cut out 01’ and erase a bit more around the edges.  However, if you’re using layers in your backdrop image, you can just erase the edges of your subject image on the pasted layer. 

§     If you’re not using layers, or working with a solid background color around your subject image, go back to the original ‘subject image cut out 01’ and readjust your ‘Magic Wand Tool’ settings as explained in Step 7. 

§     If you tried everything and there is still some of the original background showing, try the ‘Paintbrush Tool’ or ‘Airbrush Tool’, adjust the tool’s settings to a finer point and carefully paint over the unwanted color showing  through on your combined image.  Use appropriate colors that would match your new backdrop.

§     Use the ‘Airbrush Tool’, ‘Soften Tool’ or ‘Smudge Tool’ to create smoother transitions from subject image to backdrop.  The options are endless.  Explore your software’s tools to see how you can improve your final image.

Step 10: Saving your final image

§     Depending on the output usage, such as printing or online sharing, you should save your image accordingly. 

§     I recommend saving one copy of your final image in the preferred file type of the software you’re using. 

→      If you’re using GIMP, save it as a ‘.xcf’ file.

→      For printing purposes: ’Save As’ a copy of the final image as a ‘.tif’ or ‘.tiff’ file.  This format preserves the original form of your image with no quality loss.  Save, if possible, without the ‘LZW’ compression though, as some photo processors might not recognize images in its compressed format.

→      For e-mailing or online sharing purposes: ‘Save As’ a copy of the final image as a ‘.jpg’.  This file type will compress the image and it might lose some quality, but the file size is small and is easy to upload to e-mails or websites.  This is however, not a good file type for printing purposes.

§     Remember, your subject image will look different on different backdrops.  Experiment by using your ‘subject image cut out 01’, saving it as a new file and following the same steps from Step 6 – 9 with a different backdrop. 

Happy editing!