The preview program is a useful tool for viewing and working with Portable Document Format (PDF) files as described in the Rocket Yard wizard: macOS 101: Select it with preview. In part two of the guide, we look at how Preview can be used for viewing and editing images.
We use the Preview's Markup toolbar, which is usually hidden. To access the Markup toolbar, you can use the Mark up with the Preview Wizard instructions, above.
Although not a full-featured image editing app, Preview has some notable features that make it a great choice. to work with images, especially when considering that it is provided free of charge as part of MacOS.
Destructive editing, automatic storage and versions
Preview is one of the programs that work with Mac's automatic storage system. This means that Preview automatically stores a document while you are working on it. The practical aspect of this is that Preview will use destructive editing by automatically saving the changes you make to the file you are working on. In other words, if you want to switch a picture back to the way it looked earlier, chances are it's too late. Previous versions of the image are history.
For this reason, I strongly recommend that you work with a duplicate of the image file. This can be done by opening an image in Preview by selecting Duplicate from the File menu. Rename the file, and then use Save from the File menu. This will ensure that any changes do not affect the original file.
Alternatively, use the Back to Command command in the File menu to return to a previous version of the file that existed before making any changes. This means you will lose all the edits you have made, even those you might want to keep.
Remove Objects from an Image
Preview has a number of tools that allow you to select an object and a copy or remove the selected object from the image. One of the problems of selecting an object is the difficulty of performing a precise choice to isolate the object from the background. Preview offers two tools to perform this task: the selection tool, which lets you draw a rectangle, an elliptical, a free shape lasso or a smart lasso around the desired object, and the Instant Alpha tool, which can make a choice based on colors of objects.
Instant Alpha : This tool has been included in the preview app for a while. It lets you remove an object from an image or remove the background from an object. Instant Alpha works by making choices based on color selection, making it an ideal tool when there is a difference between the object and the background.
(Using Instant Alpha, you can remove the background from an object that is for example, these glasses make it easier to copy them for later use.)
The instant alpha tool is in the Markup toolbar. It looks like a magic wand, and is usually the second tool from the left in the Markup toolbar.
To use the Instant Alpha tool, make sure that the object in the image is visible in the preview window. You may want to use the Zoom In or Zoom Out icons in the default toolbar to focus more on the object you want to work with.
When everything looks right, click or tap the magic wand icon.
Place the cursor near the object above the background you want to remove.
Click and hold the mouse or pointer while dragging the cursor over the background very slowly.
As you go, you'll notice that the background is getting pink. The more you drag, the bigger the background area turns with pink. What happens is, when you drag the cursor, the Instant Alpha tool adjusts the range of color it will accept as a match. This allows you to choose more of the background that a wider color scheme is used. If you choose too much area, you can just go in the opposite direction to reduce the battle area.
Once you have selected the background, stop dragging and dropping the mouse or TouchPad button.
The pink highlight will be replaced by a dotted sample line.
Click the Delete key on the keyboard or select Delete from the Edit menu to remove the selected background.
You will probably see a sheet displayed, asking if it is OK to convert image format to PNG. This is done to ensure that the deleted areas of the image are replaced with a transparent background.
You may need to repeat the process to remove background areas near the desired object that had a different color.
Once you have removed the background around the object, you can use some of the selection tool types to select the object, and then select Copy from the file menu.
The selected object is stored on your Mac clipboard for use in other apps.  You can save the object to a file by selecting File, New from the clipboard.
Preview opens a new image file with the object you just copied.
You can then select Save from the File menu.
Smart Lasso: The Smart Lasso tool is part of the selection tool. It lets you draw a freeform selection line around the object you want to copy or delete. The smart lasso will try to adjust the selection path automatically based on color intensity. This allows it to match the object you are trying to select.
(With Smart Lasso you can draw around an object you want to select, and will automatically resize itself to follow the chart of the selected object. Photo © Coyote Moon, Inc.)  To use the Smart Lasso, make sure the desired desire is visible within the image. Adjust the zoom in or out zoom settings as needed.
Click or tap the chevron to the right of the selection tool.
In the drop-down menu that appears, make sure that Smart Lasso is selected.
Place the cursor along one of the edges of the object, then click and hold the mouse or trackpad. Begin dragging a line around the object. As you go, you will notice that the freeform line is drawn, has a thick border. Make sure the edge of the object you want to extract is within the thick line of the line you draw.
Complete Smart Lasso by reversing the object all the way back to the starting point.
Release the mouse or trackpad; The thick line will be a dotted line that clamps the selected object.
You can now delete the object (hit the delete key or select Delete from the Edit menu), or you can copy the object using the Edit menu or press the Command + C keys on the keyboard.
To save the object to be used at another time, select File, New from Clipboard. Preview opens a new image document. You can then use File, Save to save the image.
(The resulting choice [dotted lines] obtained using Smart Lasso. Photo © Coyote Moon, Inc.)
Smart Lasso or Instant Alpha?
best option for use depends on the image, how the background looks, and the sharpness of the object you are trying to extract. In many cases, you find it not a matter of choosing one over the other; Sometimes both methods are needed for a pure object recovery.
Tip: You can invert the selection for either the Instant Alpha or the Smart Lasso tool. This lets you decide what is selected: the object or background. You can find the inverted command under the Edit menu.
Tips within a tip: You can tell whether you have selected the background or object by marking the direction the dotted selection line moves. Clockwise moving dots indicate a normal choice for the tool in use; Dots moving clockwise indicate an inverted selection.
Pruning an image is a common practice that Preview can take care of for you.
You can use the Selection tool to create a crop using any of the supported forms (Rectangle, Ellipse, Lasso or Smart Lasso) to define the area of the image you want to keep.
From the Tools menu, select Crop.
You may be asked to convert the image format to PNG to support a transparent layer used in image capture.
Resizing an Image
Preview offers a variety of options for resizing an image.
(Preview lets you resize an image using the Adjust Size tool. Photo © Coyote Moon, Inc.)
To resize an image, select the Adjust Size tool located in the Markup toolbar.
Image Format Presets : To customize the image to a predefined size, use the Customize drop-down menu: to select a common image size, and then c lick or press the OK button.
Custom Sizes : To manually select a size, set the Customize menu to Custom.
You can now specify the desired width and height of the image. The image size can be expressed in pixels, inches, cm, mm, points or even as a percentage of the current size. Use the drop-down menu to the right of the width and height values to set value types.
Scale images : When you change the image size, you can choose to have the image retain its original proportions by placing a checkbox in the Scale Shelf box. Once selected, any changes you make in width or height will cause the other dimension to change to keep the proportions intact.
Resolution : The image resolution can also be adjusted to match the resolution of where the image will be used. This can dramatically reduce the file size of images used on the web, or increase the file size when using images for other purposes, such as printing.
If you increase the resolution, you may see better image quality if you add a mark in the box labeled Resample image. If you reduce the resolution, you may want to try removing the check mark from the Resample image box.
Preview has the option of performing color choices so that the image has the best appearance possible. While not as sophisticated as some color adjustments shown in dedicated image editing applications, there is still plenty of control for most applications.
(The basic exposure tools and color adjustments are available from the Markup toolbar (and menus). © Coyote Moon, Inc.).
To access the Adjustment Color tool, locate its icon in the Markup toolbar or select Adjust Color from the Tools menu.
Adjust the color panel appears. The panel allows you to adjust Exposure, Contrast, Highlights, Shadows, Saturation, Temperature, Tint, Sepia and Sharpness. It contains a histogram at the top that can be used to specify the shadow, midrange, and highlight levels.
You can also use the automatic levels, which will make the adjustments for you.
If, after making adjustments, you find the original settings was a better option, or you just want to start the adjustment process, you can use the Reset All button to return to where you started.
Rotate and Flip
latest tool to examine allows you to rotate an image in 90-degree increments, or browse an image. You will find the rotation and flip features in the Tools menu.
Preview lets you perform basic batch conversions so you can resize or convert file formats. The process requires you to open all the files you want to use a change to. You can do this by selecting multiple files in the Finder, right-clicking one of the selected files and selecting Open with from the pop-up menu.
(You can use changes, such as resizing, to multiple images you select from the preview field. Photo © Coyote Moon, Inc.)
After a short while, a list of programs appears to open the files. Select Preview from the list.
Preview opens all selected files.
Select Thumbnails from the View menu, or select Thumbnails from the sidebar icon on the toolbar.
All open files will be displayed as thumbnails in the sidebar.
Select all thumbnails in the sidebar. (You can click on the first and shift-click last, or drag to select all.)
With all the images selected, you can now use the Adjust Size tool, as described above, to change all images to a new size.
You can also use the Export Selected Image command in the File menu to switch image formats. When Export to Window opens, click the Option button to select a new file format.