Hello All,
Sorry, was out of town at the end of last week and was unable to respond and clearly needed to do more research about transparency channels.
I also think I need to give you all a more clear idea of our needs and perhaps should have started there.
I work at a retail marketing photo studio where we make images of everything and anything, apparel, lawn mowers, fertilizer, water bottles, purses, garden hose, shoes, accessories, baby carriages, cosmetics, jewelry, basically if you can buy it at a store, we shoot it. Once the image has been captured on the Photo floor, it will go through digital retouching where basic cleanup and compositing of multiple captures is performed, where applicable, a clipping path is generated around the merchandise using a variety of selection methods, and the background is knocked out, leaving a transparent frame around the merchandise, or merchandise and model, as the case may be. Sometimes an image will go through multiple rounds of retouching until it is approved. This means that there will be unpredictable names and numbers of layers, alpha channels and clipping paths in any given file.
Most of our final deliverables are pngs with transparent backgrounds, with the occasional jpg and flattened tif thrown in.
Based on last year's volume, we expect to process 125,000 images over the next year for this pilot account alone, more, if this works out and we can use ImageMagick for other efforts. That works out to an average of 479/work day, but in practice, it's more like 100/work day in the slower seasons and 1,000 or more during our peak crunch times. We're currently processing these with a Photoshop batch automation, which ties up a lot of machines and produces apple double files on our afp servers.
Here are the specifications for our png deliverables:
Color Profile: Adobe RGB (1998) (8bpc) - this value is inherent in the parent tif document
Resolution: 300ppi - this value is inherent in the parent tif document
Retain Transparency inherent in the parent tif document
No interlacing
File compression, I have only two options for file compression through a Photoshop "Save As" command, "None" and "Smallest/Slow", we use "Smallest/Slow"
We can't use clipping paths to define the transparent areas. A clipping path is a vector graphic and will not support any partial transparency that may occur in images where there are soft edges, such as a model's hair or fur trim on a coat, just to name a couple examples. I've uploaded an example of this type of file for reference here:
https://www.dropbox.com/s/vbhbeanjp7kqmky/FuzzyCoat.tif
Complete with all it's layers, paths, and channels.
As you can see in FuzzyCoat.tif the clipping path around the fur trim is very loose, the final transparency around the fur was probably generated with a soft "Eraser" tool, a "Color Range" selection, a "Quick Selection" tool or any other Photoshop tool at the disposal of our retouching staff. This is not predictable, it depends on the individual retoucher's choice to get the job done in the time allotted. If we use the clipping path to define transparency using FuzzyCoat.tif as an example, we'll end up with a big white halo - and not the pretty kind - around the hood.
The other problem with using the clipping path is the fact that it is set before the image is reviewed. It's entirely possible that an edit will be requested that will change the overall outside shape and the clipping path will not be corrected. We'll just make the edit and not revisit the clipping path - it's only used in the initial round of retouching to knock out the background.
Nor is it practical to try to make our clipping paths clockwise and counter clockwise - again, some images will be pathed with the "Pen" tool, where that could work, but if the retoucher chooses to use other methods to save time, such as the "Quick Selection" tool or a "Color Range" selection, that goes out the window.
I'm not sure the warning message "IM does not handle group layers" will present a problem, if I'm understanding it correctly. Does this refer to layer groups where several layers are grouped in the layer palette in a folder or does it just mean multiple layers? Regardless, most of these images have complex layer structures like hat.tif, but usually all layers but the current image layer are turned off or are obscured by the current image layer.
What kind of befuddles me is that this is such an easy Photoshop command to implement, so it would seem like it would be fairly straightforward in ImageMagick as well.
Hope this helps,
Ann
