Today’s Question: If I edit a photo from Lightroom Classic using Photoshop, and then bring it back into Lightroom Classic it is a TIFF file, and the file size is huge. Is there anything I can do to make it smaller? Also, should I combine layers before saving/closing in Photoshop?
Tim’s Quick Answer: While there are ways you can reduce the size of a TIFF file, I don’t generally recommend taking steps that will significantly reduce the size of a TIFF file that has been created as a derivative image based on a raw capture.
More Detail: I can certainly appreciate that photographers might be surprised (or even shocked) at the difference in file size between a raw capture and a TIFF (or PSD) image created based on that raw capture.
To begin with, all other things being equal a TIFF image will have a file size that is about three times larger than the raw capture it was created from. That is in large part because most raw captures only contain image data for a single color value for each pixel, while a rendered image such as a TIFF file will have all three color values (red, green, and blue) for all pixels. There are some other variables here that affect the file sizes, but the point is that a TIFF image will be approximately three times larger than the raw capture it was created from.
In addition, if you’ve created a TIFF image via Photoshop you may have used various layers as part of your work in Photoshop, which can also increase the file size. Additional image layers in particular can increase the file size considerably, but layer masks can also have an impact. Adjustment layers are of minimal impact.
While flattening the layers in an image will help reduce the file size, I do not recommend flattening what amounts to the master version of your image. Rather, I recommend keeping all layers intact to provide maximum flexibility in your workflow. You could also reduce the bit depth from 16-bits per channel to 8-bits per channel, but I do not recommend this due to the risk of posterization (the loss of smooth gradations of tone and color).
You can be sure that ZIP compression is enabled when using the TIFF format for images sent from Lightroom Classic to Photoshop. In the Preferences dialog in Lightroom Classic you can go to the External Editing tab, where you’ll find the file settings in the “Edit in Adobe Photoshop” section. I do recommend using the TIFF file format here, and making sure the Compression popup is set to “ZIP” rather than “None”.
Ultimately, processing a raw capture to a derivative image as a TIFF or PSD image will result in a file that is considerably larger than the original raw capture. However, I consider it to be worth the larger file size to be able to take advantage of the powerful tools in Photoshop and to preserve your work as layers for maximum flexibility.