Layered Photoshop File Sizes seem Bloated

[dale.shelton]

This is not new, BTW, but I've been trying to managing storage.  Can someone help me understand why a 60MB un-compressed RAW file with two layers (original and flattened edits) saves as 500MG to 800MB files in TIF, Photoshop RAW and PSD?  I was able to shave 200MB off of the TIF using compression, but they are still over 500MB.  I could see 60MB per layer, but this is crazy.

I attached a screen shot for an impage I just opened and then saved as a PSD.  It appeard to be about 4 times the size of the uncompressed RAW file.

I'm in CC 22.1.1 using PC.

Thanks!

Dale

[Conrad_C · Accepted solution]

It’s not that the TIFF is unrealistically large; it’s the opposite: The raw file is unrealistically small.

If you do the math for the file size of a generic image (from any source, or any application), you can work out how big it will be:

Number of pixels tall 

𝗑 

Number of pixels wide 

𝗑 

Number of bits per pixel 

𝗑 

Number of channels 

𝗑 

Number of layers 

+ 

metadata, composite preview, and so on.

If you do all that math, you will come up with a file size roughly equal to an uncompressed TIFF. That is the natural size of an image.

The raw file is unnaturally small, because it is only one monochrome channel at a certain number of bits per pixel. No layers, masks, etc. But you cannot view, edit, or print it, because raw data must first be demosaiced into RGB for any of that to be possible. It must become non-raw. That’s where the trouble starts: You see the nice small raw file, but to take it into a form that will let you do something with it, it cannot stay at that size. It must become larger.

You open the raw file in Photoshop, which converts it to RGB. Now you have three channels instead of one, resulting in a roughly 3x increase in file size. Maybe your camera shoots at 14 bits per pixel, but you opened it into a 16 bits per pixel Photoshop file so file size goes up some more due to that.

Then you add one layer, so that immediately doubles the file size. Then you add more layers, masks, channels, Smart Objects… You can see how it happens. The file size only goes up from there.

If you want smaller TIFF files, something has to give. Reducing these make the most difference:

• Pixel dimensions (width vs height)
• Bit depth 
• Number of layers 

We can be surprised by the size of today’s RGB images because for many years we all worked with 7-ish megapixel images (3000 𝗑 2400 pixels, like a typical scan that would print 8 x 10 inches at 300 ppi), at 8 bits per pixel. Today we could be opening images that are 42 or more megapixels at 16 bits per pixel: 6 or more times the pixel dimensions per side, at double the bit depth! That is a tremendous increase in the data we are capturing and editing, so the resulting PSD/TIFF files have gotten gargantuan…especially after piling on layers, masks, and more on top of that.

In a single-layer document, the file size will be smaller if the one layer is a Background layer instead of a layer that supports transparency (e.g. “Layer 1”). The file size of a layered document will be smaller if the Maximize PSD and PSB File Compatibility option is disabled (in Preferences > File Handling), because that embeds one more image that is a composite preview of all the layers.

[davescm]

Excellent explanation from Conrad C

For most cameras, that single channel raw file is only contains information at each pixel for either the red or the blue or the green in the image. There are normally twice as many greens as the other two so a 40 Megapixel image would consist of 10Mpx Reds, 10 Mpx Blues and 20MPx greens. In addition, for many cameras, each pixel in the raw file is usually stored at 14 bits.

It is only when the raw convertor is used to "demosaic" the image and produce the in between values for each pixel that we get the full image in all three channels and at 16 bit. So before we add any layers, it is not surprising that our full three channel (RGB) image with 40Mpx of information in each colour channel, and at 16 bits/channel,  requires much more storage than that raw file.

Dave

[dale.shelton]

Conrad (and Dave and JJ),

Thanks so much for taking the time for such a detailed reply.  It does make sense that a 16 bit RAW would triple in size if PS is breaking that into 3 color channels at 16 bits each.  I did not know that was the affect of the color channels.  

Thanks again - Dale

[JJMack]

Tiff can be save as layered or Flat files  with or without using data compression compression.  There are also different compression that the can be used.  PSD are normally Layerd and can be saved with or without  data compression.   How you save your file is up to you.  If you use data compression how well data compression will reduce  size depends on how much details you have for the image.   Also some layer can be very large,  A smart object layer  could have a  embedded hundreds layer object.  A document can have 8,000 layers.

There is a trade off you make with data compression.  Data compression can reduce file size and network traffic but its not free it requires processing to compress and decompress that can be very expensive when latency can not be tolerated.  Cashing Buffering and spooling  read ahead and write behind will perform better locally then data compression.  The price of storage has come down and the availability of bandwidth has increased.   Data compression is not always the best choice Data compression bloats time.