Why does rendering on a PC take 10 seconds compared to 0.25 seconds in-camera?

Hi all,

I have been using various raw converters over time, but always have been left with one question: why is the rendering process so slow? Using Lightroom 4.2 on my MacBook Pro (an 17” i7 clocked at 2.66GHz, with 8GB) it takes over 10 second to export a JPG from a raw file created by my Nikon D800E. Rendering a full size view on the screen takes about as much time. Exporting a large album of 500 pictures takes one and a half to two hours. Creating a new LR catalog and doing this all on an internal Vertex 2 SSD does not make it any faster (see also http://www.lrq.me/lyons-ssd). Other RAW convertors such as Capture NX2 are not much faster. Now I might get myself a newer, faster laptop (like the top of the line MBP Retina and 16GB) but that will at best make the process twice as fast, I assume. And it will require me to spend a whole lot of money.

Yet, the in-camera rendering does this job so much faster, like one fourth of a second. In parallel, it also can encode a compressed RAW file in the same time. So, in terms of ballpark figures, my camera is around 40 times faster at this rendering job.

Where does this performance difference come from? I understand camera’s use DSP’s for this work, whereas the rendering on the PC uses a microprocessor (LR4 does not have GPU acceleration, I understand). Since DSPs can be somewhat more efficient at dosing this task, its hard to believe the difference is so use. Why would an in-camera DSP, which may run at perhaps 1W TDP be so much faster than, in my case, Core i7-620M with 35W TDP running at full load? And if it is really a DSP issue, why would Adobe not use GPU acceleration as it does in Photoshop? (An GPU is much more like a DSP than a microprocessor.)

And if it were really the DSP issue, would it make sense to make an external DSP box that would do the rendering for LR? Such an approach is quite usual for users of demanding music software (see for instance the TC Electronics Powercore Compact). Connected to a Thunderbolt port, and rendering pictures in split seconds, I would be willing to invest. Or even better, allow the D800 itself with is USB3 to be allowed to be used as an external rendering station.

Would be interested in other people's views....

best regards,RB