Compressing one image is easy. Compressing forty of them the same way, quickly, and without turning half of them to mush is where people get stuck. This is a short walk through how we think about batch work, so you can compress a whole folder of images in one pass.
Start with the format, not the slider
Before you touch a quality slider, decide what each image is for.
- JPEG suits photos and anything with soft gradients. It throws away detail your eye barely tracks, so it packs real-world scenes tightly.
- WebP does the same job as JPEG but usually lands smaller at the same visual quality. Every current browser reads it, so for the web it is a safe default.
- PNG is for flat graphics, logos, and screenshots with sharp edges or text. Push a screenshot through JPEG and the text picks up a smeared halo.
For a mixed folder, converting everything to WebP at around 75 quality is a solid starting point. You can always keep the original format if you would rather match what you already have.
Find your quality floor once
Quality settings are not linear. Dropping from 100 to 90 barely changes how a photo looks while cutting the file a lot. Dropping from 60 to 50 saves far less and starts to show. Somewhere in the 70 to 80 range most photos hit the sweet spot where the file is small and the picture still looks clean.
The trick for batch work: find that floor on one representative image, then apply it to the rest. Pick the busiest photo in the set, the one with fine texture or a smooth sky, and watch it in the preview while you lower the quality. The moment you see blocky patches in the sky or grain in flat areas, step back up a notch. That number is your floor for the whole batch.
Resize before you compress
If your photos come straight off a phone or camera, they are probably far larger than they need to be. A blog banner shown at 1200 pixels wide gains nothing from a 6000 pixel source. Resizing to the width you actually display often saves more than any quality setting, because you are removing pixels rather than guessing which ones to blur.
Set a max width, let the height follow to keep the shape, and run the batch. Compression on top of that is the second win, not the first.
If you need an exact shape rather than a smaller version of the same one, switch the resize mode to crop-to-size. Instead of scaling, it cuts the excess off the edges to hit the width and height you set, anchored on the center or a corner you choose. That is the one to reach for when a set has to come out as clean squares or a fixed banner size.
Watermark and tidy up in one pass
The same batch run can do more than shrink files. Add a text watermark once and it lands on every image, in a corner, centered, or tiled across the whole frame, with the size, color, outline, rotation, and opacity you set. In the same pass you can nudge brightness, contrast, saturation, blur, sharpen, or opacity, or drop the set to grayscale. It is one preview and one apply, so a folder of product shots can come out resized, watermarked, and evenly adjusted without opening a separate editor.
Check the outliers, not every file
You do not need to inspect forty results. You need to inspect the two or three that were always going to be hard: the darkest photo, the one with the most fine detail, and any screenshot mixed into the set. If those hold up, the easy ones already did.
That is the whole method. Pick the format for the job, find your quality floor on one hard image, resize to the size you show, and spot-check the outliers. The batch image compressor runs entirely in your browser, so you can try a dozen settings on a real batch without a single upload.