Image Compression Checklist for the Web
By Dik Raci · Creator of online tools
A practical checklist for choosing an image format, checking dimensions, reducing image file size, and reviewing the result before publishing.
Why a checklist helps
Image compression is not one universal setting. The useful choice depends on the source format, image content, dimensions, transparency needs, destination and the visible detail that must remain. A short review before publishing can prevent an image that is unnecessarily large, blurry, incorrectly cropped or incompatible with the intended workflow.
1. Start with the source and destination
Keep the original file until the downloaded result has been opened and checked. Record the source filename, format, width, height and file size. Then write down where the output will be used: a web page, a product listing, an email, a document or a social post.
The destination matters because a hero image, a thumbnail and a document illustration rarely need the same dimensions. Do not reduce quality before deciding whether the image is already larger than the display area requires.
2. Choose a format for the job
Use JPEG when the image is a photograph or contains continuous tones and does not need transparency. Use PNG when sharp edges, transparency or a limited-color graphic are important. Use WebP when the target workflow supports it and you want a modern web image format. Consider AVIF when the target browser and delivery workflow support it and you have checked the converted output.
Format choice is a trade-off, not a ranking claim. A smaller file is not automatically a better file if it loses an important detail, removes transparency or cannot be opened by the target workflow.
3. Check dimensions before compression
If an image will be displayed at a smaller size, resize a copy to a sensible maximum width or height before comparing compression settings. Record the new dimensions. Avoid enlarging a small source file just to meet an arbitrary pixel target; upscaling may make edges or text look softer.
For responsive pages, check whether the publishing system creates suitable variants. If it does not, keep the source and output dimensions documented so the page does not load a very large file for a small visual slot.
4. Compress the image and compare the output
Use an image compressor online or a local workflow to create an output. Record the settings that were available, the output format, the file size and the dimensions. Compare the source and output at a useful viewing size rather than relying only on a percentage shown by a tool.
Inspect photographs for block patterns, ringing around edges, banding in gradients and loss of small text. Inspect graphics for broken transparency, color changes and softened lines. If the output is larger than the source, keep the source or try a more suitable format instead of forcing the result.
5. Open the downloaded file in its real workflow
A successful download does not prove that an image is ready for every destination. Open the file in the browser, editor, CMS or document workflow where it will be used. Check that the color appearance, transparency, orientation, dimensions and filename are still correct.
If the file is intended for a website, verify that the HTML uses descriptive alternative text where appropriate, that the displayed dimensions match the layout and that the image is not loaded at an unnecessarily large size.
6. Keep a small quality record
A repeatable note makes it easier to explain a choice or reproduce it later. The record can be as small as the following table.
| Field | Example to record |
|---|---|
| Source | Filename, format, width and height |
| Destination | Page, document, email or social workflow |
| Output | Format, width, height and file size |
| Settings | Quality, resize or conversion options used |
| Visual check | Text, edges, gradients, transparency and orientation |
| Environment | Browser and device used for the review |
| Decision | Keep, adjust, convert or restore the original |
Do not present one file’s result as a universal saving or quality guarantee. Different images and settings can produce different outcomes.
Common mistakes to avoid
Compressing before choosing dimensions
A large source may remain unnecessarily large even after a quality adjustment. Decide the display dimensions first, then compare the output.
Treating a percentage as a guarantee
A percentage depends on the source file and settings. Use the actual byte values and visual comparison for the file you are preparing.
Converting every image to the same format
Photographs, logos, screenshots and transparent graphics have different needs. Test the format against the destination instead of applying one rule to every file.
Deleting the original too early
Keep the source until the output opens correctly in its final workflow. It is the simplest way to recover if a conversion or compression choice is unsuitable.
A short publishing checklist
Before publishing an image, confirm that you have selected the intended format, checked the output dimensions, compared the file size with the source, inspected visible detail, verified transparency and orientation where relevant, opened the downloaded file in the target workflow, and kept the original until the review is complete.
Related CompressoPanda tools
You can use the image compressor to compare a compressed output with its source, the batch image compressor to review several files in one workflow, the image converter to test a different format, the WebP converter for a WebP workflow, and the AVIF converter when AVIF is supported by the destination.
Frequently asked questions
What is the best image format for a website?
There is no single best format for every image. Choose based on image content, transparency, browser support and the workflow where the output will be used, then compare the actual file and visual result.
Should I resize before compressing?
If the source is larger than the display area, resizing a copy first can avoid carrying unnecessary pixels into the compression step. Keep the original and record the output dimensions.
Why did compression make my image larger?
Some images are already optimized or do not suit the selected encoding settings. Compare the byte size and visual result; if the output is larger or less suitable, keep the source or test another format.
How can I check whether an image is ready for publishing?
Open the output in the target browser, editor, CMS or document workflow. Check dimensions, orientation, transparency, visible detail, filename and the way the image is displayed on the page.
By Dik Raci — Creator of online tools.