3 replies to this topic

[M. Harry Trask]

I'm familiar with many of the ways (PS and aftermarket) of increasing the pixel resolution of an image. I was recently shown (as part of a workflow presentation) how to up-rez an image by using ACR during Raw conversion. I'm curious what you think of using this as opposed to any of the many other methods.

[adiallo]

I haven't played much with the ACR upsampling. Some people like it, but I can't recall hearing anyone say it was noticeably better than PS bicubic smoother. Upsampling can be content dependent to a degree. But in my experience digital camera files upsample with less apparent degradation (and also print better at lower resolutions) than film scans. Really the only way to put your mind at ease is to test a sampling of your images using ACr and PS. Then compare the results onscreen and in print. If one method is consistently more pleasing than the other, you've made your choice.

[M. Harry Trask]

I'm not sure that I'm really capable of seeing minute differences in images. So I try to evaluate technologies based on understanding what they are and how they work. The guy that showed me this one said "I dunno, that's the way I was shown how to do it". I searched Adobe.com to see if I could find any reasonable documentation for ACR, but came up empty-handed. So I'm curious whether there is any inherent advantage to upsampling during RAW conversion, or even which one of the many algorithms (bicubic, sharper, smoother, etc) they actually use in ACR.

[adiallo]

M. Harry Trask, on Sep 7 2007, 09:58 AM, said:

So I'm curious whether there is any inherent advantage to upsampling during RAW conversion, or even which one of the many algorithms (bicubic, sharper, smoother, etc) they actually use in ACR.

No inherent quality advantage in upsampling in the raw converter. Resampling is applied only upon export, when pixels are fully rendered, so none of the usual raw editing benefits apply with regard to making up or throwing out pixels. Back in Bruce Fraser's original edition of Camera Raw, he implied that ACR upsampling was very similar to PS Bicubic Sharper. Unless you get Thomas Knoll to reveal the exact algorithm, that's probably as close as you'll get to an engineering answer.
In PS, for upsampling you want to use Bicubic Smoother, while for downsampling Bicubic Sharper is preferred.