What resolution needed for 4x6 ?: Printers and Printing Forum: Digital Photography Review (2024)

I want to save some everyday / nothing special photos to later print at 4x6

What resolution is minimum for good quality prints?
Can I just do a batch save at Low or Medium resolution?

How about 256kb 3872x2592 (that's the low resolution default) or should I save at Med resolution?

Please remember, these are all "nothing special" photos.

Is there a formula for this?
--
Thanks...

Rich

http://www.flickr.com/photos/proparoo

What camera do you have that has a low resolution default of 10 MP? What software are you using?

There is generally no improvement in print quality over 300 PPI (pixels per inch). So, for a 4x6 you need 4 inches x 300 PPI = 1200 pixels for the short side and 6 inches x 300 PPI = 1800 for the long side. In other words, there is no improvement in print quality over 1200x1800 pixels.

However, you also specify 256 kb (which presumably is the file size) and 10 MP. This must be an extremely compressed file and this will reduce the image quality considerably. I suggest that you save the files at a smaller resolution and much lower compression.
--
Chris R

Chris R-UKwrote:

What camera do you have that has a low resolution default of 10 MP?
What software are you using?

There is generally no improvement in print quality over 300 PPI
(pixels per inch). So, for a 4x6 you need 4 inches x 300 PPI = 1200
pixels for the short side and 6 inches x 300 PPI = 1800 for the long
side. In other words, there is no improvement in print quality over
1200x1800 pixels.

However, you also specify 256 kb (which presumably is the file size)
and 10 MP. This must be an extremely compressed file and this will
reduce the image quality considerably. I suggest that you save the
files at a smaller resolution and much lower compression.
--
Chris R

Chris,

sorry to disagree, but I tested this ages ago. Took a large scan (11MP) and downsized it, same edge size but different resolution. The files got printed on a Canon i850 inkjet. Starting at 600 dpi down to 75 dpi. My wife and I could still see an improvement between 300 dpi and 400 dpi. Neither of us saw anything between 400 dpi and 600 dpi. In particular for small prints I use 400 dpi. When doing larger prints I am happy with 300 dpi.

There might be a difference if you were to use a different printer. Canon inkjets are native 1200 or 2400 dpi, so 300 and 400 give a good match (divisible without rest). When using an Epson 360 dpi might be better. Dye-sub printers sometimes ask for mad numbers such as 315 dpi. Dye-subs tend to be more fuzzy about this.

joachim05wrote:

... Took a large scan
(11MP) and downsized it, same edge size but different resolution.
... My wife and I could still see an improvement between
300 dpi and 400 dpi. ...

If you downsized the file (resampled in photoshop), then you were not printing each test from the same file. It's possible that the differences you saw were due to the photoeditor's resampling algorithm, and not the printer's ability to use the added resolution.

Normal human vision is generally considered to be able to resolve fine black-and-white details of about 0.5 minute-of-angle. A minute is 1/60 of a degree. We're talking just over 0.5 inch (13 mm) at 100 yds (91 m). If we assume you look at the print from 18 inches (0.46 m), the 0.5 minute-of-angle means the smallest detail a person with normal vision can resolve is about 1/382 of an inch (0.067mm).

That is why you see quotes of about 1/300 dpi as the general recommendation for sharpness in a print. As long as the blur of unsharpness is smaller than about 300 dpi, the print will look sharp. As viewing distance increases, the size of the dot can increase commensurately.

Notice here I'm speaking "dots per inch" because most hardcopy displays--inkjet, lithography, et cetera--will normally have been laid down by the printer in dots or lines as the smallest image element.

When you're dealing with the digital image in your editing tools, it's better to think in terms of pixels per inch because that's the increment the tools are working with. So your image prepared for viewing at normal reading distances should be around 300 ppi, and that's what you'd send to the printer.

When the pixel size is significantly greater than 300 ppi at normal reading distance (say, 200 ppi), the eye begins to see the image as discrete pixels (pixellation). That's where interpolation (uprezzing, upsampling) comes in. The sole purpose of interpolation is to keep the pixels below the limit of human eye resolution.

As people will always tell you, interpolation can't create detail where there is none, and that's true. But pixellation is so ugly to the eye that viewers will object to pixellation long before they begin to object to unsharpness (unsharpness is natural--pixellation is blatantly artificial). So if you must have a given image size, it's better to interpolate than not.

Don't be confused by the printer's dpi. Remember that an image pixel can be any of millions of tones while the printer is only working with four to twelve tones. A printer dot must be much smaller than the pixel it's printing because it has to mix (dither)several dots to approximate the tone of the pixel. So you would need a printer of, say, 1440 or more dpi capability to print a 300 ppi image.

In practice, don't even worry about the dpi of the printer. Unless you're really involved in working with Raster Image Processors (RIP), modifying the default dpi is not something you need to consider. It's a lot easier to make it worse than to make it better.

Bottom line to answer your question: A small print will be viewed at normal reading distance, so set your ppi in the editor to 300 and change the dimensions to 4x6. Don't change the dpi of your printer.

This app also means you do not need to save multiple versions of files at different dimensions...it just applies the resizng to the original size at the moment of printout.

I find that my sharpening requirements vary enormously depending on print size, so I resize, then sharpen, and save that resulting file.

RDKirkwrote:

... That is why you see quotes of about 1/300 dpi as the general
recommendation for sharpness in a print.
...
... I'm speaking "dots per inch" because most hardcopy
displays--inkjet, lithography, et cetera--will normally have been
laid down by the printer in dots or lines as the smallest image
element.

From the rest of your post I'm not sure you meant to say the part I quoted. But just to set the record straight, the usual recommendation for ink-jets is 300 or so pixels per inch --not dots per inch. Pixels/inch are determined by the number of pixels in the file and print-size. Dots/inch are determined by the printer and the print-quality settings you've chosen.

As an example, Epson printers print multiples of 1440 dots/inch, regardless of the file reolution (pixels/inch). Epson's 1440 dots/inch allow exactly 4 dots/pixel from a 360 pixel/inch file. Because 360 goes into 1440 an integer number of tirmes (no interpolation is needed), many suggest 360 pixels/inch as the best resolution for printing with Epsons.

From the rest of your post I'm not sure you meant to say the part I quoted. But just to set the record straight, the usual recommendation for ink-jets is 300 or so pixels per inch --not dots per inch. Pixels/inch are determined by the number of pixels in the file and print-size. Dots/inch are determined by the printer and the print-quality settings you've chosen.

We're talking about two things occuring at once on the print. The resolution of the eye is about 300-whatever-you're-talking-about per inch. Whatever element is being used to build the image, if it's larger than 300 per inch, the eye will resolve it as individual elements rather than a continuous line or tone.

1. Pixels. The printed pixels must be at or about the 300 pixels per inch or the eye will resolve the individual pixels. If the pixels are being printed by dithering much smaller dots, those dithered pixels must still be below 300 pixels per inch.

2. Halftone dots. The dots must be at or below the 300 dots per inch or the eye will resolve the individual dots. Those of us who remember early computer printer graphics know how important that is.

As I said in my post, unless one is getting into the guts of RIPs, one doesn't need to think about what an inkjet printer is doing with its dots.

Because 360 goes into 1440 an integer number of tirmes (no interpolation is needed), many suggest 360 pixels/inch as the best resolution for printing with Epsons.

The problem with this supposition is that the printer doesn't lay down the dots precisely side by side.