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I would like to create a 60 inch x 20 inch canvas print using an image with a resolution of 4759x1798 (240 pixels per inch) and I would like to know if the image quality will still be good at that size.
To generalise the question, what is the recommended maximum size of an enlargement at varying image resolutions?
e.g. 3 megapixel, 5 megapixel, 8 megapixel, etc
It all depends on the distance you want to view the image from.
A billboard(20'x60') might look completely fine with an 10MP image, that is as low as 5dpi.
I personally have printed canvas prints from images as low as about 70dpi without issues. They look great. Before I send them off though, I use software to resize them to the desired output. Most if not all labs that create canvas prints will also have similar software to do this, but I prefer to do it on my own. I use Perfect Resize from OnOne Software.
To answer your specific question, will you be able to create a 60"x20" canvas from a 4759x1798 image? I think you will just barely be able to squeak by. It isn't going to be "art studio" quality necessarily or be able to be scrutinized very closely, but that isn't typically the purpose of a canvas print.
As noted by other answers, you will have to crop the image on the short end to achieve that aspect ratio though. Since you are already starting with a low resolution image, you may want to alter the aspect ratio of the canvas to get every last pixel that you have out of the image rather then cropping further.
I have seen people turn old Facebook photos into canvas prints at 16"x20". Is the quality good by my standards, no. But they are completely fine with it as we all have different levels of acceptable quality. Also, they aren't viewing it from up close, so it really isn't a problem.
I would talk directly with the company you're using to produce the canvas prints.
In general, I try to print at 300 ppi on photographic paper and 200 ppi on canvas. I've gone as low at 100 ppi on canvas with good results. Yours is just going to be slightly lower resolution.
The closest I have to what you're doing is a 3600x2400 image printed on canvas at 3 ft by 2 ft. That's 100 ppi. It's fine. It isn't meant for up-close viewing. The success of the image doesn't depend on fine detail. Canvas isn't the best medium for fine detail, anyway.
When it comes to printing large, the native image size out of the camera doesn't mean much. A 60x20 inch print is very large, and print resolution is measured in PPI, or pixels per inch. Even the highest resolution cameras of today, such as 18mp-24mp sensors, do not produce enough native resolution to be printed that large...most top out around 17x20 native. Your physical print resolution for a 60x20" print is 14400x4800 pixels @ 240ppi. For reference, thats a 69mp image...about three times higher resolution than the highest resolution DSLR sensors on the market today.
Your going to need to do some digital enlargement to achieve that, and you'll need to do some careful sharpening or use specialized tools to do so without softening the image too much. You will also want to make sure you know the type of printer that will be printing your photo. It is important to keep the image resolution relative to the native print resolution of the hardware you'll be printing with...otherwise the printer driver or rasterization software will do additional scaling for you. That could (and often does) compromise the hard work you put into careful enlargement in the first place.
Epson ink jets, including the commercial variety, have a native print resolution of 720ppi (note, print resolution and print DPI, or dots per inch, are not the same thing...DPI in print is usually quite a bit higher, such as 2880x1440.) The standard resolution for most other ink jet printers, both both personal and commercial, tends to be 600ppi. You will want to make sure that you resize your images to an evenly divisible ppi of the printers native, so that no additional resizing is performed during a print. For Epson printers, you will want to use something that divides 720 evenly, in which case 360, 240, 180. For other ink jets (so long as they are not unique devices with unique resolutions), you want something that divides 600 evenly, in which case 300, 200, 150. The difference between the two is minor, however you may wish to choose 360/300 depending on how you intend to mount the print, and how close your viewers will be able to get.
When it comes to actually choosing a print resolution, it will really boil down to how much original resolution you have, how much larger the print will be, how close you want your viewers to be able to view the print from, and how much effort you are willing to put into scaling and sharpening to preserve the necessary detail level. If you are going to hang the print in a location that precludes closer viewing, go with the lowest resolution...180/150ppi. That would require enlargement to 10800x3600/9000x3000 pixels. If you intend to hang the print in a location that allows your viewers to get within 4-5 feet (say middle of a standard wall behind a couch), you'll probably want to use 240/200ppi, which requires an enlargement to 14400x4800/12000x4000 pixels. If you intend to hang the print in a location that allows your viewers to get within 3 feet, and want to keep drawing them in with more detail, you'll want to use 360/300ppi. This latter scenario is more rare, and is only really necessary when you really want to draw your viewers in. In this case, you need an enlargement to 21600x7200/18000x6000 pixels. I have two walls in my house along hallways that do not even allow the viewer to get more than a few feet from the print, and I opt for 300ppi or more for any prints that hang along these walls.
It should be noted that if you do not have much resolution to start with, say 8mp or less, then there is no point in trying to preserve detail with 300ppi. With such a low starting resolution, your some eight times lower than you need for such a large print. No matter how you massage your pixels, they will never enlarge well enough for a 300ppi print...or even a 200ppi print. Your better off sticking with 150ppi, and saving yourself the trouble. If you are not starting out with 16mp or more, maybe even 18mp, you might not want to bother with 300ppi either, and just go with 200ppi. Once you move beyond a 3x enlargement, its extremely difficult to preserve fine detail. You might be able to handle a 4x enlargement from 16mp to 69mp, but its going to require a lot of effort. Finally, don't bother enlarging beyond 150-200ppi if there is not much fine detail to start with, or if fine detail does not matter. Landscapes, macro shots, bird and wildlife and the like usually have a ton of fine detail. Architecture, sports, most man-made objects, portraits, etc. generally do not contain the kind of fine detail that you need or want to preserve, so stick with the lowest resolution and save yourself time and effort.
I have written a small study on using iterative bicubic scaling to achieve extreme enlargements here on PhotoSE: Emprical Study: Extreme digital upscaling. You can use iterative bicubic to preserve fine detail, or you can try using one of the several enlargement programs tested to preserve fine edge detail (S-spline and fractal scaling do well maintaining edge definition, where Bicubic breaks down.)
When I printed a big canvas the company said their canvas printer was 150dpi. I had to enlarge my 10Mp image slightly (from 100dpi to 150) and it still looks really good. you will be going from 79dpi to 150 dpi with your image and intended size.
What you can do is measure your monitor and view it at a zoom level so it shows the right amount of pixels per inch on your screen - first 79 and then resize 1.9x and step away form the monitor and see how it looks. Lanczos algorithm is a good algorithm to use for this.
If your image is really good, I think it is safe to resize up to 2x before printing, for canvas due to the texture nature and you want to step back for a good view maybe even x3-x4, but do it yourself, not the printer, so you have control over the algorithm. But if it has lots of noise and the sharpest areas are still kinda blurry, you already used the grace to get the original size.
Canvas prints are often easiest to print when compared with prints to be made on high art or glossy photographic paper. The reason is that the texture of the canvas removes some of the need to show super sharp detail. The detail becomes subsumed into the material texture of the canvas to an extent. The weave coarseness can help the photographer where insufficient pixels are available within the captured image. Another factor to consider is what the viewing distance will be. The general rule is that the observer should be standing (at least) between 1.5 and 2 times the distance of the image diagonal, away from the canvas.
The appropriate resolution will always be based upon viewing distance and how much detail you want to be visible to the observer. Your chosen resolution of 240ppi mandates that the 60 inch side will need to contain 14,400 pixels and the 20 inch side will utilise 4,800 pixels. These numbers are derived by simple multiplication. 60 x 240 and 20 x 240. One more simple piece of arithmetic multiplies 14400 and 4800 together (the answer is 69,120,000) and we can see that you will require 69 megapixels to achieve your target resolution.
This is usually way beyond what can be easily managed by skilled hobbyist photographers. My own camera is a full frame, compact, mirrorless model and it does not manage to capture more than 24.3 megapixels. It was quite recently updated and yet it still only manages to capture 42.4 megapixels. We could look at medium format and we see that the medium format Leica only captures 37.5 megapixels. Hassleblad does produce 50 megapixel files and by some multi-shot pixel shifting it can produce 200 megapixel files. Now we are getting somewhere but the dollar costs are stratospheric.
What can the ordinary photographer do? There are many techniques for increasing the apparent resolution of an image inside Photoshop, until we get to the point where there are enough pixels in the image to permit printing. There are also software solutions which claim to be able to increase image size. What is happening is that these methods use interpolation... which is a smart method of saying that photographer's invent more pixels between the ones that we actually do have. Falsifying the pixel count can work, if the viewing distance is sufficient and there is not too much detail to be seen.
Another commonly seen technique is to reduce some of the image detail so that the image tends towards emulating a water-colour painting. This can work well because it does not require the observer to see any of the image detail in great depth. One piece of interpolation software that I have had some successes with is Resize Sense... A batch image resizer. It was not very expensive at $11 and it does a reasonable job. It may only be available for the Mac.
Your first question requires you to have a 69 megapixel sensor in your camera. Failing which you need to find a way to quadruple your available image resolution. (I have assumed that you are using a camera with a resolution minimum of around 18 megapixels) Your second question about maximum size of enlargement must depend on why you want to enlarge the image from the state it was in when first captured. Web resolution is generally around 100 ppi and it can be as low as 72 ppi if you can be sure of how it will display in many different browsers and operating systems.
When printing, you should take into account the surface of the print, the viewing distance, the purpose of the print, whether it will be under glass or in the open, ink specifications, dot gain, screen angles and ink coverage. It is generally a safe rule of thumb to assume nothing less than 300ppi is going to be good enough but 240ppi and 180 ppi are acceptable resolutions where the viewing distances are sufficiently wide enough to assist the observer with seeing a continuous colour image. Banding and pixels are not going to be acceptable artefacts.
My past experiences have shown me that all images, destined for a professional printing house; should be supplied as PDF files. This ensures that the image will appear just as you had laid it out and the print house will not be able to mess with it in any manner. Any textual elements will not require you to send your own fonts (for which you have paid) to the print shop. They will be able to prints all text as it is. Embedding the colour space in the file (to match that used by the print house) will also guarantee that The image on your screen is precisely what the printer will print. Check before laying up the final file to be sent to the printer any of their own requirements for specialist coloured inks (Pantone CMYK or Hexachrome etc) registration marks, colour separations and flattened files that can be read by the printer.
Ensure that all work is formally proofed and signed off by you before agreeing to the final print run.
If the picture is meant to be viewed as a whole, 6mp is enough for every size of the printout. The human eye does not have a better resolution if the viewer is far enough away to see the whole image.
However, if you print e.g. a landscape and viewers are expected to look at small details by getting close to the picture, then a higher resolution is required.
