Most monitors will display at 72
ppi., unless adjusted, but that is generally dependent on the graphics card. Printers print at whatever it is told to print. If you want it to print at A3 it will adjust the
dpi to suit. This could mean printing at 1200 DOTS per inch or 50
dpi.
(although I dont think many printers will print at 1200 dpi, it has been a while)
When you look at the properties on most camera for resolution, they will display something. Canon are 240 dpi, Nikon if I recall are 72. Neither matter without the other two dimensions (number of pixels recorded length and breadth)
As a general rule of thumb, to work it all out, use 200 dpi (dots for printing) as a minimum, and 150 as an absolute minimum if you are desperate. Take the resolution of the image (right click on the file and go to properties). Divide 200 into the dimensions, and that will give you a good idea of physical size that you can print up to. For canvases, as these can give an effect of softening the image anyway, we used to warn customers if we couldnt get 150 dpi out of an image for the size they required. The software though, was very good, and could manage to interpolate from an equivalent of 80 dpi.
To make the maths simple on an 18 mp camera, let's say pixel dimension of the sensor is 6000x3000 pixels = 18,000,000 pixels
.
For a high grade art print (galleries etc), I would not print larger than 20 inches by 10. (6000/300dpi and 3000/300dpi).
Regular prints (for the house etc). 30 inches by 15 (200dpi)
Canvases 40 inches by 20 (150dpi)
There is an additional consideration. If you are considering a massive print, you generally look at it from a distance, so dpi becomes less of an issue. Look at a billboard up close, and you can see how low the dpi can go, yet still be effective. (I have read of as low as 6-8 dpi).
Wet printing a digital image (as you would get at Jessops, Boots etc), is a completely different ball game using lasers, dyes and photographic paper and is a lot more forgiving. This is not used for printing canvases though.
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As far as 'improving' the image, I would consider cropping into a square format or portrait format, as there is a too much dead space on the left and right of the image. If it must be a landscape format image, try cropping out the right hand side grass, leaving some on the left for Oscar to 'look into'. The image is sharp and focused on my screen. My monitor is no longer calibrated, so I cannot say anything about the colours.