Pixel size and file capacity are different
The horizontal and vertical pixels are the resolution of the image, and KB·MB is the amount of stored data. For example, if you reduce a 2000×1000 image to a width of 1000 while maintaining its proportions, it becomes 1000×500. The number of pixels is reduced from 2 million to 500,000, but the file size is not exactly quartered.
File format, compression settings, and how colors and details are stored also affect capacity. If you are using a file that is too large to display, first reduce the output width to compare. Enlargement only increases the number of pixels and does not restore details that were not in the original.
Comparison of WebP·PNG·JPEG
| Format | Compression method | Transparency |
|---|---|---|
| PNG | Lossless | Support |
| JPEG | Typical web photo storage has lossy compression | Not supported |
| WebP | Loss/No Loss | Support |
References: MDN image format guide
References: Google WebP Guide
First check what format the service you are uploading the photo to accepts. Toolzip allows you to save as PNG, JPEG, or WebP, but it cannot change the upload conditions of the site or app to be delivered.
Toolzip's WebP saves use the browser Canvas encoder. The fact that the WebP format supports lossless is different from saying that the tool provides the ability to select a lossless mode. There is currently no WebP lossless mode selection in the tool.
Three steps to reduce capacity
- Keep the original and set the output width. Start by checking the size you need for where you want to post.
- If you need to maintain transparency, compare PNG or WebP. When you select a JPEG in Toolzip, transparent areas are filled with white.
- For JPEG and WebP, change the quality and save, and check the downloaded file size and the letters and outlines on the screen.
Toolzip's initial quality value is 85. This does not mean that 85% picture quality is guaranteed, but is a setting value passed to the encoder. Compare the lower saved file with the original to see if it's good enough for your purposes. There is no single optimal quality value for all images.
When PNG is selected, the quality values in this tool are not used to adjust compression quality. If you want to reduce PNG size, adjust the output width, or check transparency and sharpness and compare with WebP results.
References: quality parameter in MDN Canvas toBlob
Criteria for comparing conversion results
| Check items | How to check |
|---|---|
| Capacity | Check the actual bytes and KB of the downloaded file |
| Sharpness | Compare small letters, borders, and repeating patterns to the original |
| Transparency | Check boundaries on light and dark backgrounds |
| Output size | Ensure width and height are sufficient for posting position |
Saving as PNG does not bring back details that have already been lost. Saving an already compressed JPEG as PNG avoids new lossy compression, but does not restore information lost in the previous JPEG compression. Starting with the original whenever you change sizes or formats makes it easier to maintain a baseline for comparison.
Scope of support for Toolzip image converter
Input is PNG·JPEG·WebP of 20MB or less and 25 million pixels or less. The output width is limited to 1~8,192px and the height is limited to 8,192px or less, with a total of 25 million pixels or less. Height is calculated based on the original ratio. The quality input range is 10 to 100.
Because this is a method of creating a new image in Canvas, preservation of original metadata such as EXIF is not guaranteed. It also does not provide the ability to preserve animations. Photos are processed in the browser and conversion files are downloaded separately.
Frequently Asked Questions
If I change to WebP, does the capacity always get smaller?
No. It depends on the original format and degree of compression, image content, output size, and quality settings. You should compare download results yourself.
Can I specify a target size, such as 100KB or less?
The tool does not automatically target a file size. Adjust the output width and quality, save the image, and check the resulting file size.