Resolution rendered by printer

GA
Posted By
George_Austin
Feb 21, 2008
Views
327
Replies
11
Status
Closed
If you uncheck the resample box when enlarging an image you maintain the number of pixels in the image, lowering the image resolution. But, according to Tim Grey:

From 2/20/2008 QUOTE"…the image will be interpolated at the printing stage (for example, most photo inkjet printers render the data at 360 ppi)".END OF QUOTE

Thus, if you don’t resample (interpolate) in Photoshop, the printer will do so for you. I am having a hard time accepting this Tim Grey advisory. Do "most" ink jets really render at a fixed resolution (300, 360, whatever), or do they render at the resolution specified by the user?
Related Tags
print resolution

Master Retouching Hair

Learn how to rescue details, remove flyaways, add volume, and enhance the definition of hair in any photo. We break down every tool and technique in Photoshop to get picture-perfect hair, every time.

RB
Robert_Barnett
Feb 22, 2008
Well one way to find out would be to print an image at 6×6-inches at 72dpi and print one at 6×6-inches at 360 dpi and see how they look. I would be very surprised if any printer driver takes a 72dpi image and ups it to 360, they would be having major complaints about poor image quality.

Robert
GA
George_Austin
Feb 22, 2008
Robert,

Followed your suggestion. The printed images were indistinguishable. Not sure what that proves. Did the printer render both at the same (360ppi) resolution or was the interpolation ineffective?

Aside: I’m sure you agree, it’s ppi not dpi.

George
G
Greg
Feb 22, 2008
wrote:
If you uncheck the resample box when enlarging an image you maintain the number of pixels in the image, lowering the image resolution. But, according to Tim Grey:

From 2/20/2008 QUOTE"…the image will be interpolated at the printing stage (for example, most photo inkjet printers render the data at 360 ppi)".END OF QUOTE

Thus, if you don’t resample (interpolate) in Photoshop, the printer will do so for you. I am having a hard time accepting this Tim Grey advisory. Do "most" ink jets really render at a fixed resolution (300, 360, whatever), or do they render at the resolution specified by the user?

Yes, it’s true. Most good printers these days require images at a fixed ppi, 600 for Canon and 720 for Epson. If you send an image at a different ppi to the printer, the printer driver will interpolate the image to the required ppi.

The rub comes when the driver doesn’t do the best job, depending on the interpolation method embedded in the driver, like bicubic perhaps.

Worse still is if the image is interpolated in the image handling software, then re-interpreted by the printer driver. The result is not optimal by any standard.

The best solution I have found is Qimage, a specialist printng program which uses Lanczos interpolation, a far more sophisticated algorithm than bicubic. Process your image in Photoshop, and size it in Image/Image Size *without any resampling*. Just leave the ppi where it falls. Then, use Qimage to print the image, which will resample the image up to the required ppi in one operation with Lanczos, and feed it to the printer with no further resampling.

The single resample with Lanczos results in a far better print than other methods.

Note that ppi and dpi are not interchangeable terms. Images are sized by ppi, the number of pixels to the inch. Fewer pixels to the inch gives a bigger image. A 2000 x 3000 pixel image – 6 megapixels – printed at 300ppi will yield a print 2000/300 x 3000/300, about a 6.67 x 10 inch print. Bigger print, lower ppi.

DPI, dots per inch, describes the printer characteristics. My printer, a Canon i9950, prints at 4800 x 2400 dpi. When fed with the required 600 ppi image, each pixel of the image is represented by a matrix of 8 x 4 dots of ink. 4800 dpi to print a 600 ppi image is 8 dots to the pixel, and the other way gives 4 dots per pixel, a total of 32 dots of ink per image pixel.

This allows the printer to mix colors within each pixel for smoother tone.

Colin D.

—
Posted via a free Usenet account from http://www.teranews.com
N
nospam
Feb 22, 2008
"Colin_D" wrote in message
wrote:
If you uncheck the resample box when enlarging an image you maintain the number of pixels in the image, lowering the image
resolution. But, according to Tim Grey:
From 2/20/2008 QUOTE"…the image will be interpolated at the printing stage (for example, most photo inkjet
printers render the data at 360 ppi)".END OF QUOTE
Thus, if you don’t resample (interpolate) in Photoshop, the printer will do so for you. I am having a hard time accepting this
Tim Grey advisory. Do "most" ink jets really render at a fixed resolution (300, 360, whatever), or do they render at the resolution
specified by the user?
Yes, it’s true. Most good printers these days require images at a fixed ppi, 600 for Canon and 720 for Epson. If you send an image at a different ppi to the printer, the printer driver will interpolate the image to the required ppi.

Just to add, not all inkjet printers are limited to either 600 or 720 for their "native" resolutions. But on most consumer Epsons and Canons, when resampling it’s best to stick to an even multiple of the printer’s interpolated resolution, e.g. 300 ppi for Canon and 240 or 360 (or for most 1-bit images, 480) ppi for Epson. This almost always yields the best results.
RK
Rob_Keijzer
Feb 22, 2008
Isn’t it so that a printer *has* to interpolate because otherwise gaps would appear between pixels as they are printed wider apart?

Or are the individual pixels simply printed larger in that case?

Rob
DM
Don_McCahill
Feb 22, 2008
Aside: I’m sure you agree, it’s ppi not dpi.

Actually, on a printer it can be dpi. On a monitor it is always ppi.
GA
George_Austin
Feb 23, 2008
Rob: Pixel size is NOT constant, image-to-image. And by varying the number of printer dots within the array of printer dots comprising a pixel, "bit depth" or "tone" is achieved.

Don: But it is IMAGE resolution (ppi) we are concerned with here.
LH
Lawrence_Hudetz
Feb 23, 2008
Printers produce dots, not pixels.
DM
dave_milbut
Feb 23, 2008
Printers produce dots, not pixels.

not mine. dye subs are continuous tone.
I
ID._Awe
Feb 23, 2008
stochastic FM anyone.
GA
George_Austin
Feb 23, 2008
"…Printers produce dots, not pixels…"

And the matrices of dots formed by printers produce pixels.

I’ll buy "stochastic FM"

How to Improve Photoshop Performance

Learn how to optimize Photoshop for maximum speed, troubleshoot common issues, and keep your projects organized so that you can work faster than ever before!

Related Discussion Topics

Nice and short text about related topics in discussion sections