# Frequently asked questions
- Is it possible to change also images which are already uploaded?
- Have installed and enabled XT Adaptive Images and Jotcache, but images are not scaled?
- Do I have to change/adjust breaking points?
- To test, I am navigating with my desktop browser and simulating different page sizes, Ok?
- Which image is rendered according to the device resolution?
# Is it possible to change also images which are already uploaded?
Yes. XT Adaptive Images (opens new window) works for all uploaded images. Even if you delete the folder of adapted images, it will also re-generate them. Additionally, if you re-upload an image, it re-generates it as well.
Finally, XT Massive Image Optimizer (opens new window) is also designed to process all images in batch processing.
# Have installed and enabled XT Adaptive Images and Jotcache, but images are not scaled?
- Please, check the following quick setup https://www.extly.com/docs/others/xt-adaptive_images_/overview (opens new window)
- Have you enabled both extensions and JotCache Configuration for devices?
Once you install and enable both extensions, images are resized according to the user device.
Remember to configure JotCache device-dependent cache (opens new window) (otherwise, you have one cache for the whole site and devices):
Joomla! 3.5.1 has included a new alternative for Platform Specific Caching, this new feature provides a similar functionality:
Please, test with a simple big image in images/ directory and verify the generated images. For instance, in our site, the extension page https://www.extly.com/utilities/xt-adaptive-images.html generates these images:
# Do I have to change/adjust breaking points?
About breaking points, you can configure them according to your needs.
By default, plugin implements general breaking points. From a performance point of view, small images are very similar and more breaking points do not offer any gain. A mobile device can easily resize them on the fly to render the page.
# To test, I am navigating with my desktop browser and simulating different page sizes, Ok?
The best way to test is with several real devices and screen sizes.
Desktop browsers can simulate different screen sizes, but the most accurate tests are only achieved with real devices.
Take into account that the plugin has a resolution cookie. If you change the page size to simulate devices, then you must manually remove the "resolution" cookie between tests. For instance, this is a sample resolution cookie for a simulated iPhone 5/SE:
# Which image is rendered according to the device resolution?
These are the variables that affect how an image is rendered:
- Each device has a screen size.
- The browser has a page size, smaller than the full size of the screen.
- The image has an available canvas, calculated dynamically by the browser, where the image is displayed.
- The user can visit the page in landscape mode so that the coordinates can be inverted at any time.
we recommend keeping the default resolutions: 1382,992,768,480. They represent the average breakpoints that work for most devices, and they are tested on a full set of resolutions.
The plugin uses a resolution cookie to detect and calculate the best breakpoint. The plugin delivers the best image in the image src attribute according to the detected resolution. If resolution falls in the middle of two break points, then the plugin delivers the best resolution for that case.
Finally, modern browsers support the srcset image attribute, and the plugin can also generate all images to fill it according to the breakpoint. In this way, the browser knows the available files to choose the right image according to the available space. For instance: even if the device has a big screen if the browser detects a small canvas for the image, and the srcset declares a lower resolution image, then it picks the right image for the case.