Why Image EXIF Info Might Differ from Caption
Some images on DIGLLOYD sites might have EXIF info that differs from what is shown in the image caption. The caption is always correct; the EXIF info might or might not be correct, as shown below.
The explanation follows below.
Layering loses EXIF ==> other solution needed
Here at diglloyd.com, lens rendering aperture series and similar comparisons are frequently created. To create these series, layered Photoshop files are used along with a sophisticated set of javascript scripts. However, since Photoshop retains EXIF for only the base image in the entire set of layers, EXIF is lost for all layers but one*.
Thus when saved via a scripting system for series, the EXIF will correspond to one of the layers, but not any of the others. N-1 of N images will have incorrect EXIF. For example, if the aperture series is from f/2 through f/22, the EXIF for all images will end up being for, say, f/2 or f/8 or whatever.
This shortcoming of Photoshop is why the correct info is stored in the layer name as shown below. Since scripting creates the layer names from the standalone image file(s), there is no chance of error. When saved (also via scripting), the correct shooting information is taken from the layer name and embedded into the Description field of the EXIF info for each image. This is how the DIGLLOYD server obtains the correct shooting information, including certain other metadata (focus stacking and other flags/info). Continues below...
* There is no API in Photoshop to associate EXIF with a layer in an image. Nor is there any way to strip all the EXIF info yet leave in the needed information in the Description field that the server needs to properly display the true shooting info in the caption. For that matter, much of the EXIF cannot be replaced (read only), so there is no solution to making correct EXIF info for layered images.
How captions are generated
At runtime, the server-side code extracts the correct information from the Description field and creates the caption under the image with the correct information, in real time.
Because it is all script-driven and the information is never entered by hand, there is no possibility for error in the captions derived from this Description field. But the EXIF shooting information may be wrong for the reasons explained above.
(the technical shooting data stuff)