Optimizing image quality can be a time consuming process as many factors contribute to rendering acceptable results. The outcome is partly subjective because individuals perceive image quality differently. Structured experimentation is key.
Adobe Experience Manager includes more than 100 Dynamic Media image delivery commands for tuning and optimizing images and rendering results. The following guidelines can help you streamline the process and achieve good results quickly using some essential commands and best practices.
Best practices for image format (&fmt=)
JPG or PNG are the best choices to deliver images in good quality and with manageable size and weight.
If no format command is supplied in the URL, Dynamic Media Image Delivery defaults to JPG for delivery.
JPG compresses at a ratio of 10:1 and usually produces smaller image file sizes. PNG compresses at a ratio of about 2:1, except sometimes, such as when images contain a white background. Typically though, PNG file sizes are larger than JPG files.
JPG uses lossy compression, meaning that picture elements (pixels) are dropped during compression. PNG on the other hand uses lossless compression.
JPG often compresses photographic images with better fidelity than synthetic images with sharp edges and contrast.
If your images contain transparency, use PNG because JPG does not support transparency.
As a best practice for image format, start with the most common setting &fmt=JPG.