Batch processing is useful when several files need the same kind of preparation. It is not a substitute for checking the result: a mixed folder can contain photographs, screenshots, logos and transparent graphics that need different settings.
When batch processing is appropriate
Use a batch when the files have a similar purpose, format and target size. A product-photo folder is a better batch than a folder mixing a logo, a screenshot and a camera original. Keep the originals in a separate folder before processing.
A safer workflow
- Select a small sample first and process it with the settings you intend to use.
- Open the downloaded files and compare dimensions, format, transparency and visible detail with the originals.
- Only then process the remaining files. Keep a record of the source folder, settings and date.
- Check several outputs from the beginning, middle and end of the batch. Look closely at text, faces, thin lines and transparent edges.
Settings that should not be assumed
There is no universal quality value or reduction percentage for every image. Photographs tolerate different settings from screenshots; a conversion to a new format can also change transparency or compatibility. Choose the output format and maximum dimensions according to the destination, not according to a fixed promise.
Failure and memory checks
Browser processing uses the device resources available to the page. Very large files, animated images or a large selection may take longer, fail individually or require smaller batches. If one file fails, keep it separate and record its format and dimensions instead of silently replacing it.
What to record
For a useful internal record, note the number of files, formats, dimensions, settings, files that failed, input and output bytes, and the visual checks performed. These observations are specific to the selected files and should not be presented as a universal benchmark.
A decision table for mixed folders
| File type | First check | Risk to inspect |
|---|---|---|
| Photographs | Display width and format | Detail, gradients and faces |
| Screenshots | Text and sharp edges | Blur, halos and unreadable labels |
| Transparent graphics | Alpha channel | Fringing on light or dark backgrounds |
If the batch does not behave as expected
Reduce the number of files, try one representative file and note whether the failure follows the file or the batch size. A browser tab can also be affected by available memory. Treat a partial download as an incomplete result and do not replace the source folder until every required output has been opened.
A useful handoff for a team
When a batch is prepared for another person or a CMS, include the source folder name, the settings used, the date, the number of successful outputs and any exceptions. This makes the result reviewable and prevents someone from treating a single successful sample as proof that every file is suitable.
A useful handoff for a team
When a batch is prepared for another person or a CMS, include the source folder name, the settings used, the date, the number of successful outputs and any exceptions. This makes the result reviewable and prevents someone from treating a single successful sample as proof that every file is suitable.
Sources and further reading
web.dev: Image performance explains why correctly sized images, format selection and measurement matter. MDN’s image format guide compares common browser formats.