Pixel density revisited

Started Oct 22, 2008 | Discussions thread
bobn2 Forum Pro • Posts: 61,414
Re: Print driver resizing

DSPographer wrote:

chuxter wrote:

OK, you say...first normalize the sizes by using PSE...then reduce
the overall size by reducing everything by 50%. That works, but it
seems to be testing the characteristics of the PSE resample engine
more than anything else! Is there any data to show that PSE (or any
other editor) doesn't introduce small errors when taking 3 pix and
resampling them at 50%m 55%, and 74%? With this uncertainty, how can
we ever truly compare apples to apples???

I think we are trying to answer the same question: how to compare
apples to apples when starting from different image sizes? Even when
comparing prints the images will have been "processed": the print
driver will typically do some interpolation; then when viewing the
image depending on viewing distance your eyes will average over a
small area of the picture. In my opinion a high quality resizing
algorithm can recreate this effect in a well controlled way. As long
as the algorithm and standard image sizes are carefully chosen the
ranking of two cameras should be affected less by resize algorithm
errors than by such things as print driver settings like output
sharpening amount.

No test is going to give a completely accurate indication of the results any particular photographer will get form their workflow. Short of producing outputs for every permutation of tool and parameter setting, there is no way of doing it. Morever, when you get a new camera, you adjust your workflow to get the best results for you. What is needed is a test with enough supporting information for an informed user to make a judgement of how it would work for them, and an 'at a glance' usability that isn't going to mislead the uninformed user. The trouble is with the 100% crop is that it meets neither of those objectives. The resized crop will do both. At a glance it will give an indication of likely relative output quality, with the normal caveats. For the more informed, after gaining first impressions, if you know the workflow behind the test, you can make a judgment on how that relates to your own.

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