Dramatic File Size Growth


Today’s Question: I am getting a bit challenged by file sizes from my new camera. My raw files are typically about 52MB. If I do nothing other than open one in Photoshop and save it as a PSD file the size jumps to over 250MB, 5 times the raw file size. When I work with the image it gets to over 1GB. The file 16-bit, ProPhoto RGB, 300 ppi. Do I just have to suck it up and get a large, fast SSD drive?

Tim’s Quick Answer: My personal recommendation would be to accept the larger file sizes for your master images after processing. There are, however, some things to consider if you want to reduce overall file storage requirements.

More Detail: The relatively large size of your raw captures reflects primarily the resolution of the image sensor in your camera. As a very general rule the raw file size in megabytes will approximately match the number of megapixels on your camera’s image sensor. There are, however, a number of variables that can impact this file size, such as compression applied as part of the raw capture format.

The file size of the processed image reflects the fact that the raw capture has been processed to contain all available pixel data. Generally speaking the base-level processed image without compression will be three times the size of the original raw capture. That is because for most raw capture formats each pixel only stores one value (red, green, or blue) rather than the full RGB data for the processed image.

If you are opening the raw capture via Camera Raw as a Smart Object, that will also increase the file size, because the original raw capture is then embedded as part of the master image.

If you use the Maximize Compatibility option when saving a Photoshop PSD (or PSD) file, that will double the base file size for the image. For example, a PSD file saved without layers that is 120MB in size would become 240MB in size if you use the Maximize Compatibility option. Note, however, that Maximize Compatibility is required for PSD images you want to import into Lightroom.

Within Photoshop each additional layer you add will also increase the file size. Adjustment layers have very little impact on file size, but duplicating an image layer will have a big impact. It is therefore a good idea to avoid duplicating a layer when you don’t need to. For example, for image cleanup you can generally use an empty image layer for the cleanup work, rather than making a copy of the Background image layer.

Another option that impacts file size is the bit depth. The base file size will be doubled when you choose a 16-bit per channel bit depth rather than 8-bit per channel. However, especially if you need to apply relatively strong adjustments to the image after the initial raw processing, using an 8-bit per channel bit depth can lead to a loss of smooth gradations of tone and color in the image.

Of course, if you’re comfortable with the idea you could flatten the final version of your image and then convert it to the 8-bit per channel bit depth. Saving that final version and discarding the larger master image that includes layers would result in less storage space consumed. But it also means you couldn’t return to your layered master image if you decided to make changes to the image at a later date.

If you’re using a high-resolution digital camera, you’re going to end up with large files. And if you use a non-destructive layer-based workflow in Photoshop, your master image files are going to be quite large. Some of the steps noted above may help reduce the overall size of files you’re creating, but at the end of the day you’re probably going to just need to accept that you are going to consume a lot of hard drive space with your images.