Today’s Question: I thought that if you flatten a Photoshop file, you could “Save As” a JPEG. So why use “Save a Copy”? Save As seems to accomplish the same thing?
Tim’s Quick Answer: The “Save As” command in Photoshop will only allow you to save an image as a JPEG if the image is fully compatible with the JPEG format. That means the image can’t have any layers, layer masks, or saved selections, and that it must be in the 8-bit per channel mode, for example.
More Detail: As noted in an answer last week, the “Save As” command in Photoshop will now only allow you to save in a file format that supports all features of the current image. If the image has layers, for example, you can save in the Photoshop PSD or TIFF file format (among others), but you can’t save as a JPEG. To save a JPEG without altering the image to be compatible, you can simply use the “Save a Copy” command.
There are a variety of features in Photoshop that can’t be preserved as part of a JPEG file, among other file formats. The inability to save a file in a format that doesn’t support all features of the file is aimed at helping you ensure you don’t accidentally save a file without preserving all elements of the file.
If you wanted to save a layered image as a JPEG you could certainly flatten the image first. However, this includes the risk that you might accidentally fail to retain the layers in a supported format. The Save a Copy command will cause a new file to be created in any file format, without replacing the primary image.
Layers, however, are not the only feature of Photoshop that can’t be included in a JPEG image. Besides having no layers, JPEG images can only be saved in the 8-bit per channel mode. They can only be set to the RGB or CMYK color mode. They can’t have any layer masks, alpha channels, or saved selections.
You could certainly make changes to the image to make it compatible with the JPEG format so you can use the “Save As” command. However, it is easier to not worry about the specific features you may or may not have taken advantage of for the image, and instead use the “Save a Copy” command when you want to save an additional image file beyond the master image. That master image should generally be saved as a Photoshop PSD or TIFF file in order to preserve all features you’ve taken advantage of.