Interpolate in Photoshop or Not?

[HSakols]

I'm still unclear when making a print that challenges the resolution of my digital camera whether it is best to allow photoshop to interpolate and set my print resolution to 360 dpi OR is it best to keep lowering my print resolution to about 180 dpi?

[bill t.]

I feel it is always better to let PS re-interpolate your image to your printer's "native" resolution which is 360 for Epson and 300 for Canon.  At least on my Epson printer PS interpolation is much better than printer-driver interpolation, particularly when it comes to high contrast diagonal edges and fine details like grasses just a few pixels wide.

[Farmer]

I'm yet to find a print that is "much" better for being 360 on an Epson rather than 325 for example.  The matrix and the half toning and the LUT just aren't so simple as to say 360 is always better.  If you have PS create pixels, the printer will just represent them and it may or may not make an impact.  If you're over 240 and not doing really really fine straight diagonal lines or text then I wouldn't worry.

Ultimately, though, test it for yourself, but believe me you can make high quality prints from as little as 120 depending on what you're doing.

[sesshin]

From my experience printing from Lightroom offers better interpolation than in Photoshop. Just let your image ppi fall where it may and then set the print ppi at whatever your printer's closest native resolution is (180, 240, 360, etc for Epson). Produces prints as sharp if not sharper than interpolating to 360 in PS.

[Dan Wells]

The Canons are actually 600 (or 300, you can choose) dpi through the plugin (although 300 only through the driver). As I understand it, anything that isn't at the printer's native resolution gets interpolated by the driver, using a fairly primitive method (at best bilinear, sometimes just nearest neighbor). If this is true, the best workflow would be to interpolate to a native resolution using the best tool you can find (ideally a high-end interpolation plugin such as Genuine Fractals (which is what I use, but there are others), or potentially Lightroom, which as I recall uses the sophisticated Lanczos algorithm). Photoshop is still a better option than the print driver, because its bicubic variants, while inferior to Lanczos or fractal interpolation, are superior to anything printer drivers can do. The exception to "never let a print driver interpolate" is Qimage, which is often thought of as a print driver, but in fact has quite sophisticated interpolation algorithms.

                                                         -Dan

[NikosR]

From my experience printing from Lightroom offers better interpolation than in Photoshop. Just let your image ppi fall where it may and then set the print ppi at whatever your printer's closest native resolution is (180, 240, 360, etc for Epson). Produces prints as sharp if not sharper than interpolating to 360 in PS.

What's the straightforward way of seeing the image ppi in Lightroom? Sort of making a trip into PS, memorizing the camera to print size relationship or making the calculations myself, I haven't find a way of having LR display the ppi the image will be printed at without interpolation relative to the print size.  

Am I missing something or is LR treating us as dummies here? The only option I can find is either turning Print Resolution off (thus sending native resolution to the printer driver) or 'blindly' select a resolution for LR to interpolate to, without having any info about what resolution this interpolation will take place from.

[NikosR]

Answering my own question... If you have show guides active (View -> Show Guides and View -> Guides -> Dimensions) then if you unckeck the Print Resolution box, the native image ppi will be shown along with its dimensions on the image info overlay. Subtle would be an understatement...


So, just looking at an image here from the D700 I want to print at A3 with margins, the image info shows a native ppi of 261. Should I leave it at that, interpolate down to 240 or interpolate up to 360 for printing on my Epson 3800?

[Wayne Fox]

Answering my own question... If you have show guides active (View -> Show Guides and View -> Guides -> Dimensions) then if you unckeck the Print Resolution box, the native image ppi will be shown along with its dimensions on the image info overlay. Subtle would be an understatement...


So, just looking at an image here from the D700 I want to print at A3 with margins, the image info shows a native ppi of 261. Should I leave it at that, interpolate down to 240 or interpolate up to 360 for printing on my Epson 3800?

For an Epson printer from Photoshop, I recommend leaving it at the native resolution and let the driver handle any interpolation in the screening process.  After seeing Jeff Schewe discuss this approach on the "From Camera to Print" video, I found it delivers excellent results with a far simpler workflow.

I saw mention in this thread of print drivers using weaker algorithms than Photoshop, but even if you do a bicubic interpolation in Photoshop, unless you are changing the resolution in an even amount (50%, 200%, 400%), I don't think Photoshop can use a pure bicubic algorithm either.

Side by side tests to me show no difference.  I have a few images where a 200% uprez, followed by output sharpening, and then sending that new native resolution to the print driver yielded a better result than an uprez to exact size in Photoshop (which required an uneven interpolation).

[JBerardi]

Answering my own question... If you have show guides active (View -> Show Guides and View -> Guides -> Dimensions) then if you unckeck the Print Resolution box, the native image ppi will be shown along with its dimensions on the image info overlay. Subtle would be an understatement...


So, just looking at an image here from the D700 I want to print at A3 with margins, the image info shows a native ppi of 261. Should I leave it at that, interpolate down to 240 or interpolate up to 360 for printing on my Epson 3800?

In my own experience printing out of LR to a 3800, I'd say 360. The best thing you can do, though, is just run a test for yourself. Make a test strip, print it at all three resolutions, see what they look like.

[sesshin]

So, just looking at an image here from the D700 I want to print at A3 with margins, the image info shows a native ppi of 261. Should I leave it at that, interpolate down to 240 or interpolate up to 360 for printing on my Epson 3800?

iirc in the LR2 video on this site Jeff Schewe recommends 360ppi for images which fall in that range