The amount of times I have received requests for information on the ins and outs of printing resolution. I have read many an articles and to be frank none of the put it very simply. Here is my version.
You own a printer and you own a digital camera or have some digital images you wish to print just how big can you print and still have it look good. Well it amounts to several factors but the best one is whatever looks good to you. This sounds very amateurish and am sure some of you might wince at my short answer, but really if you are happy with the result then that’s an important factor. But if you are not happy then maybe you are viewing it too close, viewing distance is also another factor. Seriously do you look at an A3 picture from 10 inches away or do you stand back and admire the picture for what it is ? Well you should view it from a distance that is right for the size of image. If you’re too close then you may see the digital artefacts or pixels that the image is made up from, this is most likely to happen on larger photos than 10×8 inches or on posters
Printers often have an enormous printing resolution of for example 4800x 2400 dpi, dots per inch. You can immediately get confused if you try and equate this with the resolution of you image, for example your cameras resolution is 2816 x 2120 or 6 million pixels, so if you print the image using the printers maximum res. Then surely your image will appear less than an inch big ?? well yes but that is not what should happen. You cannot literally equate the two devices in this way, ill explain
Commercial printing presses used to publish books etc always request images at 300dpi as that what works for them, actually this is a good optimum printing resolution for us too, and this can be used as a base for our printing equation. Simply what ever your image is in size it can be printed at 300 dpi. Well actually its ppi or pixels per inch, as you camera or image is digital and in pixels, not dots like a printer. For example even a 640 x 480 resolution image can be 300 dpi but will only measure just over 2 x 1 inches achieved by simply dividing the dots per inch into the pixel size of the image. When we get larger images such as 2816 x 2120 we can see that at the optimum printing resolution of 300 dpi we spread those pixels over 300 pixels per inch and get a image size on paper of 9.4 x 7 inches.
The simple printing rule.
After your Photo Restoration is complete, scale you image across the page at somewhere between 250 to 300 pixels per inch to give you an optimum print. If you need to go bigger then just scale to 200 pixels per inch or even less. Do a test and see how it looks. If it looks good go for it.
When you set your printer going set to maximum resolution and use the best paper you can afford.
NOTE: Don’t get confused again with the maximum resolution of your printer being 4800 x 2400 dpi as this is just how much ink going down on the page used to print those 300 pixels per inch you scaled across the page earlier.
The continuing conundrum
I often speak to printers who tell me they need a large file size in order to print to a predetermined size. It is cast into the conversation "it must be at least 18mb". When asked why, the response is more often than not because I need it big to work with I know what I can do with a large file. My point I try to make is that I can make you a large file if you wish but do you actually need it. A typical TIFF of a 6 mega pixel image is 17MB. Anyway the print houses want large files but we can make them larger but the dimensions will remain the same so how will they benefit by having a larger file. If we convert the file to 16bit per channel in Photoshop the file size will swell enormously as the colour information contained in the image is now so much greater. I’m am certain that this will not benefit the printers in anyway as they still have the same 6 million pixel image we started with but a file size up in the 34mb region, then if we convert to CMYK it reaches a massive 46mb !!
Here is a break down of how this worked
6 MPixel 2816 x 2120 1.7 mb JPG 8 Bit/channel RGB
6 MPixel 2816 x 2120 17 mb TIFF 8 Bit/channel RGB
6 MPixel 2816 x 2120 35 mb TIFF 16 Bit/channel RGB
6 MPixel 2816 x 2120 46mb TIFF 16 Bit/channel CMYK
Photoshop converted the 16bit per channel. This was completely unnecessary but done to illustrate a point that a large file can be obtained fro 1.7mb JPG. Most software’s (in fact I don’t know of any) can’t edit a 16 bit per channel image, as there is just too much information to process, It is normally converted to an 8 bit per channel image 8 RED + 8 GREEN + 8 BLUE = 24 bit colour for RGB or 32 bit colour for CMYK which can then be processed by most editing software’s.
