Under the hood

Each image in the editorial database has associated a version number. This is a 32 bits integer that is set to 1 the first time a image entry is created, either dummy or real, and that is automatically incremented by the upload process each time the same image is processed again.

Fred4 caches images in memory. The ImgRefresh command compares the version number of the images in memory with that in the database, and if the latter is greater, meaning that the image has been uploaded, Fred4 reloads it.

Re-loading a page it is not enough to refresh the images in it, because if a image is used in more than one page it is possible that when a page is loaded the image is already in the cache, because it has been loaded together with another page - and in this case Fred4 does not load it again.

Even deleting and inserting again a image is not enough to reload it from the database, because when a image is deleted a copy is kept in the undo list, so it is still in the cache, and when it is inserted again the cached copy is used.

Each time a image is inserted in a page or updated Fred4 stores in the page's image element the version number and the size of the image.

Each time a page is loaded or the images are refreshed Fred4 compares the version number in the page element with those of the image. If the version number of the image is greater it means that it has been processed again - and so potentially modified - since it was last placed on page or updated. In this case Fred4 marks the image as 'modified' and displays it as a crossed rectangle containing the name of the image followed by '+'.

To put back in the normal status images that have been marked as modified it is necessary to use the ImgUpdate or ImgUpdateEx command. Depending on their parameters, these commands may update all the selected images, adjusting the size of the image box or cropping to the new size of the image - if the size has changed, or leave the images in "to-be-updated" state, if the difference between dimensions of image box and image itself exceeds the tolerance.

•ImgUpdate command checks the image against the bounding box on page.

•ImgUpdateEx command checks the image against the previous version of the paginated image. This prevents losing the scaling and crop position when updating an existing image that has been reprocessed and which width and height differ slightly from the existing one.

•ImgRefresh command compares the version number of the images in memory with that in the database, and if the latter is greater, meaning that the image has been sent again to the OPI, Fred4 reloads it. The command uses the parameters configured in Edit >Preferences > Automatic Refresh' dialog box. To refresh the images contained in the read-only layers you have to check the 'Also on read-only layers' flag and set the resizing tolerance greater than zero.

•Update automatically images that did not change size when loading a page: set in Edit > Preferences > Automatically update images on refresh and on load. See Enabling images refresh on page loading or refresh.

See also

Troubleshooting images refresh and update