Why 600ppi resample for Canon iPF5000?

[jbn]

I've asked this question to a lot of people, but no one has given me a clear answer yet.  

Canon's 16bit Export option seems to be a great choice for most users, however, it requires 600ppi images, or it resamples the image itself, using the wrong algorithms.

Why is this extra resolution needed?  I can see where it would give better detail if you were resizing a large image without the "resample" checkmark.  However, when you have a 16x20" print at 300ppi that is already interpolated up a little, why would you want to resample again to 600ppi?  It is not actually increasing any detail level in the image.  Furthermore, it slows down your computer, takes up twice the HD space, and adds yet another step to getting a print out quickly.  Why is Canon requiring this extra information when standard file resolutions for printing have always been between the 240-360ppi range?  Also, I always do sharpening as a last step before printing, should I assume I continue this practice after resampling to 600ppi?

[nemophoto]

Epson resamples image data to 720. Canon is simply doing the same thing based on native resolution of 600 dpi, rather than 720. All printers do some sort of image resampling in the driver. You can send an image to the Canon at 300 dpi and rest assurd that it will be fine.

[John Hollenberg]

Canon's 16bit Export option seems to be a great choice for most users, however, it requires 600ppi images, or it resamples the image itself, using the wrong algorithms.

Why is this extra resolution needed?

I think the answer is simple.  The printer is built around 600 PPI, just as the Epson is built around 720 PPI.  For either printer, you can either do the interpolation yourself, or let the printer driver do it.  None of the printer drivers use an optimal algorithm for resampling (includes Epson).  If you can see a difference (one person who did the test could, although it wasn't earthshattering) use Bicubic Smoother in Photoshop instead of letting the driver do it.  If you can't--and I haven't done my own tests--let the driver do the resampling.  This isn't anything specific to Canon.  Chris, the tech at Inkjetart, says they all work this way.

--John

[Stephen Best]

Epson resamples image data to 720.
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On the low-end models. The driver for the 4800/7800/9800 is 360 ppi by default.

[JeffKohn]

Supposedly the print drivers use "nearest neighbor" interpolation which is far from optimal. For this reason it's theoretically optimal to send the print driver an image which is already at the native resolution and therefore bypass this interpolation step. At the very least it's probably a good idea to send the file at a resolution that's an evenly-divisible multiple of the native resolution (for instance 360ppi for Epson, or 300ppi for Canon/HP). The thinking here is that even a relatively simple interpolation algorithm will do a good job when the enlargment factor is a round number such as 2x; it's when you get into fractional enlargment factors such a 1.87 or 2.39 etc that something like nearest neighbor will start to degrade image quality.

Some people don't bother, as long is the PPI of the image is over 200ppi or so they'll just send it to the printer. My workflow is to resize to 360ppi for my Epson 2400, and then apply my final print sharpening. I've tested and can't tell any difference between sending the printer 360ppi and 720ppi, but it makes a huge difference in file size and spooling time so I stick with 360ppi.

[Dale Allyn]

I've been printing 16-bit image files at 600 ppi, though I had tried lower resolutions in my earliest prints. I had accepted what some had said about uprezzing first and feeding the printer 600ppi files, and I was getting excellent results so stay with that.

Three nights ago I decided to "re-test" this process to see what differences I could see now that I'm much more familiar with the printer and have a fairly consistent workflow. The image which I chose has a good amount of fine detail in that it's a weathered pier and the planks have quite a bit of texture and fine lines. The image fills the entire dynamic range of camera's sensor (Canon 5D) and was printed at 12x18" on satin paper (just a test role I had in the printer).

The image as printed after uprezzing in Photoshop (bicubic smoother) to 600ppi was, to my eye, clearly better than letting the plug-in uprez from 300 ppi. It was also noticeably better than the file printed at 600 ppi through the Print with Preview function (regular OS print driver) in Photoshop. The differences are not monumental. They are slight, but to me noticeable enough to deal with the extra steps and large files. Many would likely find the differences too subtle to warrant the extra work.

Colors were essentially identical in all versions, using the same generic profile.

In my opinion, this printer produces beautiful results via the Print w/Preview option, the plug-in at 300 ppi and via the plug-in when I uprez first to 600ppi. But in my comparisons the latter were just enough better that it seems to wring out the best from the printer.

It's certainly possible that for certain types of image files that the extra work and file size are unwarranted, but I've not yet done a comparison on that type image. (I'm thinking softly lit portraits with blurred backgrounds, etc.)

HTH,

Dale

[Dale Allyn]

Also, I always do sharpening as a last step before printing, should I assume I continue this practice after resampling to 600ppi?
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That's how I work. I sharpen after the uprez and for me that was/is a new learning process as I'm used to sharpening at 240ppi to 300ppi.

--
Dale

[elauq]

Can this printer actually output at 600 ppi or is this just a number that works best with the driver firmware?  

Inkjet manufacturers are boastful of their dpi numbers, yet stay mum on ppi specs.  Has any independent reviewer confirmed that each pixel of a non-interpolated 600 or 720 ppi (Epson) input test image is accounted for on the output print?

[thompsonkirk]

The problem with highest-quality iPF5000 printing is of course file size, which re-defines 'printer speed':  

With its layers flattened, a 16-bit 600 ppi file for a 13.5x20.25 print on 17x22 paper is 550MB, & this runs up to 1.65GB when using PhotoKit Output Sharpener.  Thankfully this flattens back to 550MB for export to the plug-in.  On a middle-aged G4 w/1.5GB RAM, I can go out for coffee during the sharpening; & I've been reading a thick history book during the flattening.  With most of the PS work already done on previous prints or workprints, I still haven't produced more than 4 prints of this size in a day.  

I didn't realize when I got my iPF5000 that I was buying into a new Intel Mac too!

Kirk

[marcmccalmont]

I've had an iPF5000 since July, here is what works for me after a lot of experimentation. I convert the raw file to 600ppi. In PSCS2 I resize to 6"x9", 600ppi, bicubic smoother. When all adjustments are complete I use smart sharpen/lens blur. I save this as my master file. I print only with the plugin, 600dpi and let it resize (no sharpening set on the plugin). I have found this to be optimum with a reasonable file size.
Marc

[John Hollenberg]

I've had an iPF5000 since July, here is what works for me after a lot of experimentation. I convert the raw file to 600ppi. In PSCS2 I resize to 6"x9", 600ppi, bicubic smoother. When all adjustments are complete I use smart sharpen/lens blur. I save this as my master file. I print only with the plugin, 600dpi and let it resize (no sharpening set on the plugin). I have found this to be optimum with a reasonable file size.

How much difference (if any) have you seen between this method and resizing to final print size using bicubic smoother in Photoshop?

--John

[marcmccalmont]

How much difference (if any) have you seen between this method and resizing to final print size using bicubic smoother in Photoshop?

--John
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Very little if any. I tried up-rezzing to a full sized file with bicubic smoother, genuine fractals and Qimage/pyrimid/print to file and am hard pressed to see any difference when compared to the above method (letting the plugin resize a sharpened 6x9 600ppi file). The large files are not worth the hassle for a questionable improvement.
Marc

[John Hollenberg]

Very little if any. I tried up-rezzing to a full sized file with bicubic smoother, genuine fractals and Qimage/pyrimid/print to file and am hard pressed to see any difference when compared to the above method (letting the plugin resize a sharpened 6x9 600ppi file). The large files are not worth the hassle for a questionable improvement.
Marc
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I am going to add this to the FAQ, as it sounds like a good way to save time and disk space.  One last question--do you use nearest neighbor or bilinear to resize in the plugin?

--John

[marcmccalmont]

I am going to add this to the FAQ, as it sounds like a good way to save time and disk space.  One last question--do you use nearest neighbor or bilinear to resize in the plugin?

--John
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Bilinear, I'd be interested in hearing back on your results using this method
Marc

[Tony B.]

Marc, do you resize to 6x9 because its an aspect ratio of your camera or final print size?  Or is it just the size you found that works best with your workflow?

Tony B.

[marcmccalmont]

Marc, do you resize to 6x9 because its an aspect ratio of your camera or final print size?  Or is it just the size you found that works best with your workflow?

Tony B.
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It's the aspect ratio of my 5D and D80 so it is convinient. If I crop to another aspect ratio it is of course different, but I try to store a master about that size say 4.5x12 or 7.5x7.5 or 3x18, that way the files aren't too big and I don't have to resize and sharpen every time I print. or resize and sharpen for a A4 test print then again for a A2 final print, too much work. I usually upsize and sharpen at the end of my PS workflow if it looks like the image will be a keeper. Although this is a bit off the subject I'll add it here anyways because a final print is the outcome of many steps so here is my workflow:

1. RAW conversion in DXO optics (plugin usually) Dcam3 colorspace, lens sharpness .5 and retain noise detail 90%
2. Adjustments in PSCS2 (increase local contrast with filter/sharpen/unsharpmask/amount 45%, radius 18, threshold 9)
3. Uprezz to 6x9 600ppi bicubic smoother
4. Smart sharpen  amount either 45, 90 or 180 radius .9 or 1.8 (depending on the image) lens blur
5. Export to the plugin with 600ppi 2400x1200 16 pass, bidirectional, no sharpening, bilinear, custom icc profile
I'd like to know if you get good result too

Marc

[serf]

Maybe this is not directly related, but for those doing their own profiles, do you upres the target patches to 600 before sending it to the plugin?

[John Hollenberg]

Maybe this is not directly related, but for those doing their own profiles, do you upres the target patches to 600 before sending it to the plugin?

Shouldn't make any difference, since a uniform patch of color will look the same no matter what method of uprez is used.

--John

[marcmccalmont]

Shouldn't make any difference, since a uniform patch of color will look the same no matter what method of uprez is used.

--John
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I've always left them alone with no resizing or uprezzing
Marc

[Bill J]

Shouldn't make any difference, since a uniform patch of color will look the same no matter what method of uprez is used.

--John
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That's kinda what I figured, but I upsampled it anyway just to take one more variable out of the workflow equation.

-------------------

I printed a 17'x54" panorama last weekend, but I had no choice to keep the resolution at 300ppi. At 600 ppi, the image was over 32,000 pixels wide. Photoshop warned me that some applications wouldn't work for images over 30,000 pixels across. It took over 5 minutes just to bring up the Unsharp Mask dialog box, and after all that, nearly everything was grayed out under the Export menu, including the plug-in.  So I undid everything, applied Unsharp Mask at 300ppi and opened the plug-in. It printed just fine, nice and sharp.

Bill