When in doubt, start with 80%, 70-85% for the screen, and 85-95% if the details and printing are important, be sure to check the finished image.
There is no absolute correct answer to the compression ratio
Even at the same 80%, the change in volume and appearance is different for landscape photos, text images, and illustrations. The compression ratio is not a guaranteed value of quality, but is treated as a guide when re-exporting.
Purpose is also important. You can prioritize lightness in social media posts and email attachments, but you'll need to leave details behind when printing, taking photos of evidence, and checking the condition of the item.
Expand where change is likely to occur
Face contours, hair, thin letters, leaves, lattice patterns, and color boundaries are where the effects of compression are more visible. Since it is difficult to notice the problem if you keep the whole display downsized, we will also check it in 100% view.
If you notice blocky bumps, blurred outlines, or gradient steps, compare the image quality back by 5-10 points.
Next steps when capacity is not reduced
JPEGs that are already strongly compressed may not be significantly reduced by recompression. In that case, it is more effective to shrink the vertical and horizontal pixels according to the application.
PNG photos tend to be larger, so if you don't need transparency, you can convert them to JPEG or WebP. Logos and diagrams may be easier to outline with PNG.
Determine the outcome, both numerically and visually
Rather than saying "80% is safe," we judge based on two points: whether the capacity is below the desired upper limit, and whether the necessary information can be read. Even if the submission meets the requirements of the destination, the purpose will not be achieved if the content cannot be determined.
If you open the final file on another screen or destination, you will notice differences in the display depending on the app. For important images, the original and processed images are kept side by side.
Fixed conditions when comparing
It will be easier to tell the difference if you use the same image and change only the image quality.
Criteria for determining the compression ratio
- ✓Decided on the purpose
- ✓Compared from around 80%
- ✓Viewed 100% of the details
- ✓Below capacity
- ✓I saved the original
image compression
You can change the image quality ratio and compare it as many times as you like while looking at the capacity before and after processing.
image compression→This article gives general guidance. If a recipient, printer or official service provides its own requirements, follow those requirements first.
A SMALL NOTE FROM SPACEThe numbers are the course, and the sky looks like stars. Don't just look at one or the other, look at both to decide where to land.