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Subject: Re: Faux RAW Hoorah

I'm going to make a pitch for the credibility of using 8-bit conversions out of ACR. And I don't disagree with what Thomas says, indeed I already assumed that.

I've been doing 16-bit conversions out of ACR since I started to use a digital camera more than a year and a half ago. (I only shoot raw. I was already doing 16-bit scans from slides).

Recently, I ran some tests to see how important this is. I have come the the tentative conclusion that, for me, 8-bit conversions don't (and probably won't) show a difference in my results. My target print size is about 14" or 15" by about 10", from a 6 MP camera. (Using A3 paper; the results then mounted 20" x 16" for competitions and exhibitions).

The tests were to do some conversions at 8-bit, and apply adjustment layers, etc. Then, with the "damage" already done, to convert to 16-bit. In parallel, I repeated the work on those images using 16-bit conversions from the start. After flattening the layers, I put both versions of each image into the same Photoshop file, and used "difference" blending mode to see what the differences are.

There are certainly differences, typically with small numbers, from "info". Using high percentages in the view, for example 800%, I can clearly see some non-black areas. If I select the most obvious cases, so that I know where they are, then when I switch off "difference" and just toggle between the two versions, I can I see a change between them at those selection points. It is hard to convince myself that the 16-bit version is better than the 8-bit (to 16-bit) version. They just look slightly different.

And the areas of significant difference are small in the print - millimetres, perhaps. When I print these areas side by side, I can't see any difference.

But ... I spend a significant effort in ACR to get things right before I open them in Photoshop. I do all the standard things in the adjust tab get the histogram extended and balanced. Sometimes I will use control+click to put points on the Curve, then do fine-tuning where I think further work is needed. I can often do the final print with few "corrective" (rather than "added value") adjustments in Photoshop.

8-bit working gives me some advantages, so I intend to run that way for a while. If I find that it doesn't work for a particular picture, then I find it relatively easy to redo the conversion at 16-bit, and convert the Photoshop file to 16-bit and replace just the image-layers with the new version, leaving the earlier adjustment layers in place. (I normally crop and align in ACR).

If the experiment doesn't work over a period of months, I will go back to 16-bit conversions.


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