JPG exports from same Photo (RAW and JPG) have different File Size

[tanjab569]

I've been taking a photo in RAW and JPG - and editied both in Lightroom Classic 8.3 (same photo - taken in RAW+JPG together).

Of course both Pics have different file size on memory card.

What is confusing me and I don't understand:

After exporting them together I noticed the files have again a different file size - even i've exported them with exact same settings.

Both pics are 4713x7069 pixels in size, 240 pixels/inch, sRGB, etc.

The exported JPG-Version of the Pic is about 9.1 MB, the expored RAW is about 14.3 MB...

Why is the file size different and does that matter in case of large print outs?

[99jon]

No it doesn’t matter. A jpeg is a compressed 8 bit file and will always be smaller than the raw data. A full size jpeg at 240ppi and with a quality setting between 60 and 100 will usually give very good print results although 100 is probably best for very large prints. You could export in the tiff format if your photo lab can handle it but these are much larger files, usually larger than the original raw.

[JohanElzenga]

The file size of a jpeg depends on many things, not just the size in pixels (pixels/inch is irrelevant). You started with two different images; an 8 bits jpeg that already went through a lossy compression, and a 14 bit raw file that still has all its information. The exported files were produced from these very different originals, so I would have been more surprised if you ended up with two identical exported jpegs. You may see the difference in print, but not necessarily.

[richardplondon]

You are exporting different file sizes, even when selecting all the same JPG settings, for two reasons:

• the image content is different (and hence more, or less, compressible into JPG at given output settings)
• the quantity of attached metadata (informational, and a record of the LR edits) is different

The first reason is far more significant size-wise. The second presumes that full LR metadata is being included - which you can limit.

Pixels must be different if both versions of a photo have undergone differing ISO / WB / demosaicing and subsequent processing - despite both deriving ultimately from identical camera sensor output.

Most important for file size are noise reduction / smoothing / artificial grain - sharpening of various sorts - tone and hue adjustments leading to blacks and whites "clipping", etc.

You may have cloned or otherwise locally edited too. More basically: what's even SEEN IN each image version and, how that's duly rescaled for output, may differ due to cropping / lens or perspective corrections, etc.