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Thoughts of Zero One - The Print is the Thing
Typical scenario, camera A with its 14 megapixel sensor is just rubbish, look at all that noise, camera B with 6 megapixels is so much better....blah blah blah. Why do camera makers add more pixels it just makes things worse, jeeze these camera designer blokes must be idiots, and on it goes.
Now I don’t want to be rude, but this is my website so I guess I am free to express an opinion, but these forum posters really haven’t got a clue regarding photographic reality.
I will admit that any image that looks sweet at 100% view on screen will likely print well, providing that there are actually enough pixels in the image, but that does not mean that a noisy image will automatically look crook. In fact the noisy image may well look better once printed than the pristine clean image.
Lets just explore the problems at play here.
First of all most serious image makers don’t shoot images to simply look at on screen, we shoot to print. If in fact all we wanted to do was create on screen images then a 2 to 3 megapixel camera would be all that is needed at most, because anything greater than this cannot even be fitted to the highest resolution computer screen without downscaling to match the lower pixel count of the monitor.
For most purposes the print is the final product and that is what we should be judging.
There are so many variables with on screen views, lets look at them.
The resolution of computer monitors is quite variable, in the distant past monitors had as little as 640 by 480 pixels, then it was 600 by 800 and these days it could be up to around 1900 by 1200, though it is usually less. If we assume that 1920 by 1200 is about as far as we can normally go, then at most we could fit approximately a full 2 megapixel image on the screen at one time, or in other words at a 100 percent view.
Screen pixel count however has little to do with the size of the screen; we can have smaller laptop screens with 1920 by 1200 pixels and larger 24-inch screen with the same resolution. Clearly then the size of the pixels will be larger on the larger screen and thus a bit coarser, this is why some high end laptop screens look so sharp, the pixels are much smaller and have less gaps between them (known as pixel pitch).
A monitor is very different from a print and not just in terms of the pixel versus in dots concept, but rather it has a different set of limitations. Images on a monitor can display a very wide dynamic range, in other words whites can be really white and blacks very dark. This is simply because the screen is its own light source. A print on the other hand is made on paper, it can be no darker in the blacks than the ink/dye used and lighter than the base of the paper and on top of that it relies on the use of an external light source to provide light so you can actually see the reflected image.
Noise in print images often has more to do with the print engine and the printer than the file itself, I have found some printers exaggerate the noise present and some smooth the noise by default, sometimes differently dependent on the print size. I have for example printed files on Canon Pixma Printers that were for all intents clean yet printed noisy, then made the same print again with the printers noise reduction turned on and got smooth toned prints that were sharp and noise free. The lesson, you need to experiment with your printer and realize there is a considerable amount of synergy between files, printers, drivers, papers and profiles. All is not as straight forward as that 100% on screen view may have you believe.
The colour of on-screen images typically looks punchier with pure colours such as reds and yellows not being limited by issues of dyes and inks and paper bases.
One of the major issues with looking at images on screen is scaling and although Adobe have addressed this somewhat with the latest version of Photoshop CS it is likely to remain a bugbear for some time to come.
The issue is simple enough, when we have an image that has more pixels than the screen has the image has to be scaled down by the program in use and the video card in the computer so we can fit it to the screen real estate. The problem is that scaling creates little errors and can make images look soft or jagged or over sharpened and just plain horrible depending on the scaling percentage and the processing method employed to do the scaling. It is for this reason that the only way you can judge the clarity noise and quality of a photographic file is to view it at 100% so that scaling is removed from the equation. It should be noted that 50% and 25% views also give reasonably accurate representations and if I recall correctly the engineers of Adobe Photoshop recommend 50% as the best view to judge the file on for printing.
It is generally true that the higher the megapixel count of the image capture from a digital camera the higher the noise level at a pixel level will be, this is pretty much an accepted fact but I must say the latest crop of high megapixel compacts don’t necessarily support the concept as they are for the most part very clean at low ISO’s.
The flip side is that higher megapixel counts make it possible to record vastly more detail.
Clearly a higher megapixel count also means that you can print far larger before the image starts to look mushy, or lacking in detail.
So here is the choice we could have a low 2 megapixel file that is clean as a whistle at a 100% view but lacks detail and can only be enlarged to say 5 by 7 inches or we can have a 15 megapixel image that might have some noise at 100% view on screen but can be enlarged to A3 and larger without a loss of detail.
If, for example, we took the 15 megapixel image and printed it as a 5 by 7 it will likely look quite a bit sharper and the noise is very unlikely to be an issue as compared to the actual print size the noise components are utterly tiny, so you won’ t see them. Despite the fact that at a 100% view the image may look a little rough.
If on the other hand you enlarge the small 2-megapixel file to A3 it will be very soft and will also display odd artefacts and textural noise created by the interpolation process. If you resharpen the 2 megapixel file to compensate for the loss of clarity you will most likely create odd halo effects around details. The 15 megapixel image will of course look fine.
Strangely enough if you really want to make your 2-megapixel image into a nice big print, and trust me it can be done, you are actually going to have to add noise to the file to even out the tonal variations and help synthesize some semblance of detail.
Here’s a tip, take a 2 or 3 megapixel image and interpolate it up to the same resolution as the 15 megapixel image and then view the 2 side by side at 100% views, what you may well find is that the 2 meg one looks far nosier or rougher than the 15 megapixel original.
Another aspect not properly considered is viewing distance of the resulting print. If you take a low megapixel file and print it to a 6 by 4 inch print it will look fine of course and your viewing distance will be quite close. If we take a higher megapixel file such as 15 and make an A3 print we are not expecting it to be looked at from 18 inches, the whole idea is to make it a viewable hanging on a wall. In fact the larger we go, the greater the intended viewing distance, so noise in the file, even if present, is unlikely to be an issue at any viewing distance appropriate for the image once printed and used in real world applications.
Computer monitors are different of course because the viewing distance remains the same so as we enlarge the file to its 100% max view it is always going to bias towards the low megapixel file for all the above reasons, but hopefully as you can see this has little bearing on the final intended use.
So I hope this helps put the concept of prints versus on-screen view into perspective for you.