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The answer to your question is one of those “it depends” answers, because whether PSD or TIFF is larger depends on the options you set for each. In short, TIFF can be smaller if you use one of the compression options. Uncompressed TIFF is as large as uncompressed PSD. Both use lossless compression*, so they can both preserve full quality and all layers, but that means neither can be as small as JPEG which is both lossy and throws out all layers.
We know Photoshop PSD and formats are compressed by default, because there is a setting in Photoshop Preferences / File Handling that lets you disable that compression; see the picture below. That option is off by default, which means PSD/PSB compression is on for everyone unless it’s specifically disabled here. Some people turn off PSD/PSB compression because they want the fastest possible PSD/PSB save times, but they have enough storage to put up with the larger uncompressed file sizes.
To finally answer your question, below is how it more or less works out for layered Photoshop documents, depending on the choices you make. I used a Photoshop document containing an RGB image from a digital camera, an adjustment layer, a vector graphics shape layer, and a type layer, which stay live and editable in all the variations below. Note that TIFF can preserve all Photoshop layer types.
You can’t have everything, so you have to decide whether you want the smallest file sizes or the fastest save times. And saving at 16 bits per channel is almost always about twice as large as 8 bits per channel for the same options.
The TIFF filenames may list two compression types, because in the TIFF options, you can choose from file compression options and layer compression options. So TIFF LZW RLE means LZW compression for the file and RLE for the layers.
The reason the last one, DSC0702 16bpc LZW RLE.tif, is larger than even the uncompressed ones is that LZW does work oddly with 16bpc images, sometimes making them larger than the original. If you’re going to compress 16bpc TIFF, you probably want to use ZIP compression.
…when comparing file sizes to a saved .PSD document to a saved .TIFF document (with Layers) I find that the TIFF document shows a slightly larger file size. Accessing Get Info on both, the PSD save and the Tiff save, I am seeing 562.9MB for the PSD and 579.8MB for the Tiff.
By AppleAddict001
Well, it’s always going to vary somewhat depending on what’s in the file and which save options were on. But in general, uncompressed TIFF and native Photoshop are going to be the largest, TIFF LZW will be somewhat smaller for 8bpc files, and TIFF ZIP the smallest but with excruciatingly long save times.
In your example, I wonder if they would be closer in size, or if the PSD would be larger, if compression was disabled for PSD files.
Also, I didn’t bring this up in the earlier post because it was already long, but there is also the role of the Maximize PSD and PSB Compatibility option. That adds a composite version of a layered image so that other apps can show the image without having to understand Photoshop layers, but adding that composite increases the file size.
The interesting thing about Photoshop's old runlength compression, is that it's directional based on the horizontal rows, so in certain mostly artificial cases such as gradients, simply rotating the same file 90° can significantly alter file size. Photographic imagery rarely provides such a perfect example as a synthetic gradient:
In this example, the PSD files used default compression and one was simply rotated 90°.
The TIFF versions used ZIP for the file with RLE layers in both cases. You can see that the RLE used by TIFF doesn't vary as much as the runlength compression format used by Photoshop. It's my understanding that the runlength compression used by Photoshop isn't the same as RLE used by TIFF and the differences in file sizes appear to back this up.
This is only mentioned for informative purposes, for 99.9% of images this shouldn't be a practical concern.
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