So Big!

Our modern cameras have lots of pixels. This is a great benefit for us, especially if we want to make large prints. But sometimes the files we are editing can get so big we have trouble dealing with them. Why is that?


I have made the point before that our modern sensors are amazing. The camera I shoot captures 47 MPixels for each shot. That’s 47 million pixels. There are sensors that go up to 150 MPixels in some medium format camera bodies. I haven’t seen the need to move to that yet.

Why do we need so many pixels? Some will state that we don’t. That it is just pixel envy that keeps us seeking more. There is a good argument that about 20 MPixels is enough for the vast majority of applications.

That is for you to decide for your own needs and preferences. I can state that I believe the quality of our images has moved far beyond film days. Digital images produce the sharpest, most detailed, most colorful, most editable results that have ever been possible, except in some very niche applications. There is no going back.

Raw files

Raw files hold the information that comes directly off the camera sensor. There is minimal processing done. I have discussed Bayer filters and how we get color images. The Raw file is not really an image we can look at yet.

But there are some great features of raw files we need to be aware of. First, this is the closest we can get to the exact data that was captured by the sensor. Little processing has been done. All the processing and interpretation of the resulting image is ours. Among other reasons, this is a reason to always shoot raw instead of jpg files.

Second, the nature of the raw file is that it cannot be edited. The original data is always preserved. Yes, of course, I can go into Lightroom Classic (I will always call it just Lightroom from here on) and do amazing things to the image. All of the changes are saved as what are termed “processing instructions“. The original data is never altered. It cannot be altered.

One of the things this means is that years from now when I have new tools or change my mind about how I want the image to look, I can go back and re-edit it. I can even reset to the original captured bits and start over. No data is ever lost. This is a great things.

And thirdly, the raw file is relatively compact. My camera captures 47 million 14 bit resolution sensor values, each either a red or green or blue data. It is not yet “demosaiced” to expand the Bayer sensor data to full color data for each pixel. In addition certain meta data values are stored in the raw data. Things like the camera and lens information, capture time, my copyright information, etc.

Raw file size

My camera is set to do a lossless compression of the data before saving it. So no data is ever lost in the process. Looking at a randomly selected file I just shot, its file size is 58.08 MBytes on my file system. The size of my raw images varies because of the amount of lossless compression that can be done on each image.

But think about this a minute. I captured 47 million 14 bit images. This should have been 94 MBytes of data, not counting the extra meta data. I am assuming they store the 14 bits in 2 8 bit bytes. I don’t know if that is true. This means the saved raw file is even smaller than the data that came off the sensor. As I edit it and add processing instructions, the file gets somewhat larger, but seldom huge.

Photoshop bloat

Now I sent this raw file to Photoshop and immediately saved it. No editing. The file size is 229.16 MBytes! It is about 4 times larger! And I didn’t even do anything to the image! Why is this?

Well, Photoshop edits pixels, each a triple of (red, green, blue) values for each pixel. Photoshop expands the Bayer data to the flat grid Photoshop needs, This is what Photoshop works with and what is saved. That automatically makes the file at least 3 times its original size. The raw file was compressed, that probably accounts for the difference.

Now to illustrate more of what Photoshop does, I added a blank layer and used the spot healing brush to correct a couple of blemishes, very little. Saving the file again grows the file size to 548.08 MBytes! It doubled!

To continue the demonstration, I added a curves adjustment layer and saved the file again. Now the size is 632.72 MBytes.

The difference

It is clear that LIghtroom and Photoshop show very different behavior when editing images. This is because of their nature and design.

Lightroom is called a parametric editor. It does not modify the image data, Rather, it keeps a list of processing instructions to tell how to change the look of the image when it is viewed.

Photoshop is a pixel editor. It can add/delete/modify pixels at the most detailed level. You have to be careful that you do not lose the original data. It does not care. It will do any amount of change you request. And it has the power of layers to build of levels of modification. This can lead to huge file sizes.

Did you know that there are maximum file sizes for Photoshop files? Standard Photoshop psd files can only be up to 2 GBytes in size. Tiff files can only be 4 GBytes. I exceed these limits a lot. The only choice then is to switch to Photoshop’s “big” file type, the psb. It can grow much larger. Actually, it can handle us up to 4.2 Billion GBytes. That will work for a while. 🙂 Unfortunately it is not a choice to automatically use it.

Any solution?

Well, there is the “if it hurts don’t do that” solution. Stay in Lightroom for most of your image processing. Only go to Photoshop for situations that Lightroom cannot handle. This is a good strategy and I use it.

But if you have to do that detailed pixel grooming and you have to use many layers to process your image to your taste, accept it. The cost is much more powerful computers and larger and faster hard drives. I have both. It is a cost of doing business the way I want.

Editing large files in Photoshop will lead to very large files on your disk. I have a lot of multi GByte files. That is, some of my files have grown to about 100 times the original captured file size! Ouch. I can’t do this routinely. It has to be for special images that are worth the time and file size to do this.

When you have to call out the big power tool, Photoshop can do almost anything. But the cost can be high.

Leave a Reply

Your email address will not be published. Required fields are marked *