Lightroom vs Photoshop: Editing File Size Compared

Edited Sky behind complex objects

Selecting the sky accurately in all areas in this image to achieve a perfect mask, is more challenging than it first appears. Lightroom’s Select Sky does does well with clean horizons, but this image is full of tiny structural interruptions that break the sky into small areas. The large metal silos have thin metal struts and supports and the green structure has tiny railings, that cut into the sky. Lightroom often misses these small areas or softens the edges, leaving a faint halo around the structures.All of these small transitions between sky and subject require refining the mask manually. This is an example of the kind of image where Lightroom needs help to produce a clean, accurate sky mask.

With a bit of careful work, Lightroom can produce a sky mask that is extremely accurate. Lightroom has received a update in June 2026, including its Select Objects masking tool, which is a tool used in refining the Sky Mask in this image.

Photo 1. Sky Mask + Multiple Refinements

This first image is the same one used in my three‑part Lightroom masking tutorial, refine-select-sky-mask-with-add-color-range. It's ideal for a real‑world comparison, because it includes a Select Sky mask, then several refinements to produce a good quality mask of the sky through the tree. In includes a Subtract using Select Objects refinement, and a duplicated inverted mask. This is typical masking for many photos, if you want a good quality mask.

Lightroom created two sidecar files: an .acr file (0.68MB) and an .xmp file (0.05MB). Combined, that’s just 0.73MKBB added to the original 40.41 MB RAW file — a total Lightroom footprint of 41.14 MB.

Photoshop, on the other hand, stores every adjustment as pixel‑based layer data. The PSD version of this same image is 277.84 MB — more than six times larger than the RAW file and over 230 MB larger than Lightroom’s entire edit.

Photo 2. No Masks

This second image — the tree on the rocks by the water — is a simple, low‑complexity edit. No masks were used at all. The adjustments were limited to basic global changes such as exposure, contrast, highlights, shadows, and colour balance. This makes it an ideal example for showing how Lightroom and Photoshop behave when the edit is minimal and contains no local adjustments or AI masking.

This image uses only basic global adjustments, (no masks), so Lightroom adds almost no extra data. With no masks, no AI selections, and no local edits, the sidecar files remain extremely small. Lightroom simply records a handful of slider positions, so the total footprint barely increases beyond the original RAW file.

Photoshop, however, still creates a large PSD even for a simple edit. Even without layers or masks, Photoshop must store a full pixel‑based version of the image inside the PSD. This means the PSD is still many times larger than the RAW file, despite the minimal editing. This example clearly shows that Photoshop’s filesize overhead is not tied to editing complexity — it is inherent to how PSD files store pixel data.

Photo 3. Complex Background, Multiple Masks

This third image is the most demanding of the set, combining multiple local adjustments to separate the subject from a complex, distracting background. The divers have been selectively brightened, while the buildings behind them have been darkened and softened with blur — exactly the kind of layered, targeted edits that push both Lightroom and Photoshop much harder. This makes it an ideal high‑complexity test case, showing how each program handles multiple masks, selective adjustments, and background manipulation, and how dramatically the resulting file sizes can diverge when the editing becomes more advanced.

Because this image uses several local adjustments — selective brightening, targeted darkening, and background blur — Lightroom generates noticeably larger sidecar files than in the previous examples. Each mask and local adjustment adds more text‑based instructions, so the total Lightroom footprint increases, though it still remains relatively small compared to Photoshop.

Photoshop, however, expands dramatically with this kind of edit. Every adjustment layer, mask, and blurred region must be stored as pixel data inside the PSD. This makes the PSD for Photo 3 the largest of the set, clearly showing how Photoshop’s filesize grows with edit complexity.