A key feature of editing photos with Adobe Photoshop is the ability to build a file using different image layers. However, sometimes it is advantageous or necessary to remove the image layers by flattening the image. Flattening a Photoshop image is beneficial in preparing it for printing or publishing. There are disadvantages to flattening Photoshop images that make it important to save a copy of the original file.
Layers in a Photoshop file function independently of one another. Editing the different layers separately simplifies composing images and creating special effects. Photoshop organises layers in stacks, positioning one portion of the image on top of another. Flattening a Photoshop image means the program condenses all the image layers into a single layer image. The "Flatten Image" command is located under the "Layer" menu or in the layer palette menu in more recent versions of Photoshop.
Flattening an image significantly reduces the file size, making it easier to export to the web and print the image. Sending a file with layers to a printer takes longer because each layer is essentially an individual image, which drastically increases the amount of data that needs to be processed. Professional graphic designers and artists benefit from only distributing or selling flattened versions of their work. Anyone with access to the layered file could easily change the image, but a flattened image reduces the chance that someone may quickly edit the work and resell a slightly altered version.
It is difficult to edit portions of a flattened Photoshop image because it no longer contains the individual layers. Always keep a PSD version of the file with all the layers intact for future adjustments, and only flatten the image when it is completed. Flattening an image may result in some slight differences in tone or transparency when compared with the layered file. Verify that all the layers required for the image are visible, because flattening an image eliminates hidden layers.
By default, the Photoshop file format PSD saves files with all their layers. However, when saving a new file, users may choose whether the PSD file retains layers or not. The same option is available when saving the file in PDF format. Saving an image in a format preferred for web use, such as JPEG, PING, TIFF or GIF, automatically results in a flattened image file because those formats do not support image layers.