To everybody who has replied so nicely: all correct, but still... ..there's a lot more. I've worked with photoshop since version 1, and back then, there were some real limitations you had to work around. At about cs2, it became apparent that photographers and other professionals working with images wanted to be able to save more information about their files than the standard PSD offered. HISTORY states was the first attempt to meet those needs halfway, as photographers had wanted to be able to go back several steps during work, undoing a whole set of steps. Originally, the PSD file format was supposed to expand to include the history states, but implementation proved to be too much work. Instead, other options were explored. Grouping, and even multiple compositions in photoshop are now possible. But these only allowed you to build your layers and quickly copy them for multiple attempts and adjustments, without retaining information on the values used in those steps. Enter the SMART OBJECT. This single function allowed the user to place multiple adjustments onto a single layer, then go back and check the values and make adjustments. The export function was intially designed as a way to output only the final image data to file formats that were not supported in the save function, using the most compatible part of the data possible. The save for web function was designed to save files in common internet image formats with as little data storage as possible, so the images could be kept small in file size, to be handled by the web programming rather than using excess data to define how to handle it. This has become less necessary due to cheaper storage, and the growing need for copyright respect. The more recent version of the export dialog respects this, and the save as uses the more recent xml styles that web servers use to find out how to handle the images. History states are now exportable to text files. but ultimately they still leave out the values utilized in each step. They are useful for teaching the major steps of different techniques, and can even help you set up instructional videos before shooting. SMART OBJECTS are still the best way to go as you work, though they do add more memory use. The excess data that was stored in a JPEG has gone through several revisions. XML has become the standard because it is easily handled and read in almost any programming language, allowing programmers to make use of the information in various ways. Saving without that excess data invites people to steal your work. Most that I work with use a special container format on their webserver, and save a version for that, with another version saved for downloading that has all the data. Thus, the case for both methods is still strong.
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