Question regarding photo file size

CaptainNapalm · Mar 21, 2013

Lately Ive been post processing many of my photos using PSE. I start off with RAW files and then convert them to JPEGs when all the editing has been done. As I proceed to save the individual files the program prompts me to select the file size, 1 being smallest and 12 being maximum. Since my rule of thumb is to keep each photo in the 8-10mb range I usually save them in the range of 10 to 12, this usually results in a 10MB image. However, in order to post certain photos on forums or social media sites I have been forced to save the same photos as a copy in much smaller format 1 to 3 which results in the photos being just under 2MB in size. Naturally, I assumed that making the picture four to five times smaller would result in proportionally reducing picture quality but Im seeing that its not so. I opened a series of identical photos, each having a 2MB and 10MB equivalent and viewed at actual size the picture quality difference is extremely minimal and in many cases not even visible. My wife couldnt tell a difference in quality of photos either so it cant just be my eyes. Can someone shed some light on this for me? What exactly does the software remove from the photo to make it four or five times smaller if these differences are not even visible. In other words, why should I save my photos in larger file sizes? Thanks in advance!

Big Mike · Mar 21, 2013

There are two main things that we can control, that will affect the file size of our images. The first is actual size. This is how large the photo is, in pixels. Out of the camera, you should be getting files that are 4,928 x 3,262. You might crop a little bit, which would affect that.

You have to realize what your requirements are. If you are just going to post it onto a web site, then think about how many pixels wide/tall a monitor is. Typical monitor resolution is just over 1000 pixels in either direction. So to show a photo, at a reasonable size, you really only need 800 pixels (give or take).

So if they are for web viewing, you could resize the image to a smaller size then save (A COPY). This will greatly reduce the file size. For your 'finished' photo, that you will save/archive, don't resize it at all.

The next thing that controls the file size, is the compression/quality. This is the setting that you're asking about. The higher you set it, the lower the amount of compression. And yes, as you are seeing, you can compress images quite a bit, before there is any noticeable visual difference. The thing to know, is that you don't want to compress it, if you want to edit/print it in the future. And certainly don't open, save (compress), close....and repeat the cycle again and again. That will compound the quality loss.

If you want to know what is actually happening when you save an image as a JPEG, check this out. JPEG - Wikipedia, the free encyclopedia

CaptainNapalm · Mar 21, 2013

Big Mike said:
There are two main things that we can control, that will affect the file size of our images. The first is actual size. This is how large the photo is, in pixels. Out of the camera, you should be getting files that are 4,928 x 3,262. You might crop a little bit, which would affect that.

You have to realize what your requirements are. If you are just going to post it onto a web site, then think about how many pixels wide/tall a monitor is. Typical monitor resolution is just over 1000 pixels in either direction. So to show a photo, at a reasonable size, you really only need 800 pixels (give or take).

So if they are for web viewing, you could resize the image to a smaller size then save (A COPY). This will greatly reduce the file size. For your 'finished' photo, that you will save/archive, don't resize it at all.

The next thing that controls the file size, is the compression/quality. This is the setting that you're asking about. The higher you set it, the lower the amount of compression. And yes, as you are seeing, you can compress images quite a bit, before there is any noticeable visual difference. The thing to know, is that you don't want to compress it, if you want to edit/print it in the future. And certainly don't open, save (compress), close....and repeat the cycle again and again. That will compound the quality loss.

If you want to know what is actually happening when you save an image as a JPEG, check this out. JPEG - Wikipedia, the free encyclopedia

This is very helpful. Thank you!

Judobreaker · Mar 21, 2013

Saving at levels 11 and 12 is also rather pointless...
There's hardly a noticeable difference between 10, 11 and 12 because 11 and 12 were put there by Adobe for research reasons.
If you would take an original SOOC jpg file, open it up in Photoshop and save it straight away without any changes at level 11 or 12 your image will actually get bigger then the original.

Don't ask me why they did this but I've never saved any jpg at levels 11 or 12 after I found out.

KenC · Mar 21, 2013

I suggest that when you finish editing, you save the file as a PS file (.psd) or tiff file, neither of which compresses the image at all. Then you will have a completely unaltered image from which you can make whatever size jpg files you need for different purposes. Saving as a tiff file may require flattening the image first, depending on what kind of layers it has, so I prefer PS files. The PS files will be bigger than you're used to saving, but digital storage is cheap.