File Size Question

[Migintosh]

I'm going through a series of folders of images that we use for creating grocery ads. They are cobbled together from old ads so we can access a variety of images in a central location. Because of this, there are some images that are mostly identical, but with different names. I'm trying to eliminate duplicates.

I came across two images of ribs:

As you can see, they are the same image, but have the pixels arranged in different directions. One is slightly bigger, but both are 300ppi 8-bit CMYK jpgs saved at quality 12. This image is from the images placed in InDesign at 100% to show relative sizes.

Here's my question. I want to keep the better of the 2, so I'm thinking the larger one, but when I look at the info in Photoshop and the info in the Mac OS finder, they are very different:

The names are the same, except that one has a comma (the smaller of the two). Notice that the finder has the size of the smaller image at more than twice the file size, but in the Photoshop Image Size window, they are almost the same. Can anyone suggest why they are so different? I can answer follow-up questions if needed.

Thanks in advance.

[D Fosse]

Jpeg is a compressed file format. Jpeg file size tells you nothing in itself. The size depends on the compression level as well as image content.

Other formats can use compression as well, but jpeg compression is particularly aggressive. It is destructive, non-reversible and cumulative. It can squeeze a file down to 1-5% of its full size, but the price is steady degradation with every resave. A jpeg should normally not be worked on again if it can be avoided.

So in this case, you probably want the one with the least compression and damage. That's the bigger one.

[Migintosh]

Thanks, but by "bigger," do you mean the one with more pixels, since you say that file size tells you nothing in itself?

[D Fosse · Accepted solution]

I mean bigger file size (but fewer pixels). That indicates it has not been as heavily compressed as the other one. Slightly fewer pixels, but less damage to them.

Jpeg is really a special case. Normally you'd want the higher pixel count, but the jpeg compression has bigger impact and outweighs that. As can be visually confirmed by looking at the two images as posted above.

[Migintosh]

Thanks. 

[MarekMularczyk · Accepted solution]

The Image Size you see inside Image Size dialogue box (on the top as you highlighted it) is the size of the image when decompressed when opened in Photoshop. The file size you're showing in Finder is the size of the file when compressed when saved. Hence the difference.

[Migintosh]

Thanks, that's helpful.

[MarekMularczyk]

You're welcome.

[Brittany5C25]

Hello! I work for a company that has also used this rib image. Do you happen to have any idea where it was licensed from? We're trying to track down where we got it from.