when to upsize/uprez?

[mikeseb]

Assuming one needs to uprez a digital image file (with the image-quality compromises this entails acknowledged), at which point in the image workflow will this produce the best result and least damage?

1. in Adobe Camera Raw as the raw image is converted to TIFF;
2. in Photoshop as TIFF via Image | Image Size menu;
3. via Photoshop plug-in like Genuine Fractals, after most image adjustments have been made.

I have done #3 a number of times with good results for mild upsize/uprez adjustments; the added advantage is that I can work from a fully adjusted "master" image file that I only have to do once,rather than having to reinvent the wheel by going all the way back to the RAW file if I need an uprezzed image.

Advice appreciated.

[Dale_Cotton]

The first consideration is: which upsampling method does the "best" job? You need to test all methods available to you to see if you have a preference. I find that upsampling up to 150% is a sort-of cut-off point. Up to 150% the differences between the results from various algorithms tends to be subtle.

Beyond 150% the percentage of fictitious to real pixels gets more and more extreme. If I remember correctly, a 200% upsample means that 3/4 of all pixels have been manufactured by the algorithm. Gen Frac has a rather idiosyncratic approach that tends to turn small details into vaguely triangle-like shapes, but other methods tend to just produce mush.

The second consideration is: when to upsample? My own findings are that I get better results by upsampling before things that change pixels in ways other than colour and contrast - for example, cloning and sharpening.

[Jonathan Wienke]

I never bother upsizing any more, unless I'm stitching a panorama and want to be able to align frames  with better than 1-pixel (original size) precision, or I need a really large print and am adding noise or simulated film grain or some other artistic effect that disguises upsizing artifiacts. I print with QImage, and it does as good a job as any other upsizing technique I've tried, and eliminates the need for upsizing and hadling/storing extra-large upsized files in the vast majority of cases.

[Nill Toulme]

Ditto Qimage.  In addition to Jonathan's points, Qimage also does the final print sharpening for you after upresing for each print size, saving that laborious step as well.

Nill
~~
www.toulme.net

[gdeliz]

After buying an Epson R1800 about 18 months ago I noticed that a low resolution jpeg off the web looked pretty good when printed without any upressing. I tried an experiment, printing an 8X10 from a full size crop from a 5D file at 72 PPI and comparing against the same crop uprezzed to 240 PPI using bicubic smoother followed by some sharpening. I could see very little difference between the two prints but the print that was sent to printer without uprezzing had the edge where there were any differences to be seen.  So, needless to say, I no longer bother to do any uprezzing or down rezzing when printing as the Epson driver does a good job of handling it. Furthermore the old saw, which may have been true at one time, about setting the ppi to some multiple of the printer resolution doesn't seem to hold anymore for the newer Epson printers.

George Deliz