# How many pixels are enough?



## GrandMasterK (Feb 28, 2006)

I spend alot of time around digital video, hardly no time at all with photography. The best we got is 2560x1600 monitors, but generally, for video, we're in 1080p 2 megapixel land. I was wondering if photography could help me figure out just how much further resolution with TVs has to go before they just don't need to get sharper.

I hear alot of 300 DPIs being tossed around, and I wonder if that's what's been determined as "it". Basically my question is how many pixels are enough. I know size of the image is a factor so lets take it to DPI. Lets use my screen as an example. My screen is a 24 inch 1920x1200 monitor, I think it's 90 DPI. It looks good, to be honest, 1080p doesn't look so great from where I'm sitting, it actually doesnt even look as good as a DVD does on a 50 inch from an average distance back. So where's the line drawn. I've got a 24 inch diagonal picture let's say. How many pixels do I need before adding a million more, or 10 million more, a billion more, just won't make a difference as far as a human being concerned. I guess this will help me figure out what quality I should have my 3D work printed as also.


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## Rob (Feb 28, 2006)

Circles of confusion may go some way to explaining things:
http://en.wikipedia.org/wiki/Circle_of_confusion

Rob


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## GrandMasterK (Feb 28, 2006)

that all flys right by me.


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## Rob (Feb 28, 2006)

The question you're asking does not have an answer. Perceptibly, the viewing distance affects the quality - i.e. if you sit two inches from a screen, you can see individual pixels. If you sit two inches from a print, you can sometimes see the dots. 

However, comfortable viewing distance from a print is more like 30cm and 300dpi at 30cm is enough to completely fool the brain that there are no dots/lines, only smooth colour.

A TV would have say a 1000x1000 lines at approximately 1Mb per frame at 24fps. This has a viewing range of say 6ft, not 30cm. To get a perfect image, to reach the equivilent of a photograph, would require a significantly more detailed image, more lines, greater image density and faster frame rate. It just isn't needed and is questionably difficult to capture in the first place. HDTV goes a long way to improve (double) quality, but there is a balance between what is technically capable, broadcastable and necessary.

The COC thing about viewing is at the bottom of that article.

Rob


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## GrandMasterK (Mar 1, 2006)

Can you tell me what goes into calculating the file size of an image? I thought it was pixels times the bits per pixel but I'm not sure.


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## Rob (Mar 1, 2006)

GrandMasterK said:
			
		

> Can you tell me what goes into calculating the file size of an image? I thought it was pixels times the bits per pixel but I'm not sure.



This depends on the image file. All files have a header detailing their contents which uses up an amount. Additionally, some image formats have native compression using various algorithms which normalise similar areas in the image. Most image formats however, have a value for red, green and blue, to a bit depth specified i.e. 16 bit or 32 bit, so you could bodge a formula using some examples. 

Rob


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## Alpha (Mar 1, 2006)

Here's the general rule that I go by:

The native resolution of film is around 3000dpi. Therefore, I scan my negatives at around 3000dpi as Tiff's. Whatever image size that outputs its just fine with me. It is f-ing huge though. A 2 and 1/4 by 3 and 1/4 color slide usually outputs to around 550mb.


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## bobaab (Mar 1, 2006)

Are computers limited by individual pixel sizes then?  So have they gone a step further to decrease pixel size, and increasing pixel density in high def TV's?


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## ksmattfish (Mar 1, 2006)

I don't know anything about monitor or TV resolution, but I know that 72 dpi looks really good on my computer monitor, but I need 240+ dpi to get a decent print.


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## GrandMasterK (Mar 1, 2006)

Well lets take my screen for example, compare it to a photo. My screen is 24 inches and at the farthest, my eyes are usually 2ft away from it. If it was a photo, how many pixels would you want the image to be made of knowing it's as sharp as it's gonna get as far as a human being is concerned.

720p xbox 360 games look better on the monitor then the 1080p trailers. I at first found it funny that they would make the 1080p look bad enough in compression that 720p 360 games looked better. My only floating theory on this is they compressed on smaller screens, and werent as aware of the picture degrade. It kinda sucks because while most people drool over 720p and 1080p trailers (since most people don't have hd-dvds and blu-rays yet), I sit here and go "meh". If I scoot back about 5ft though, well, that's a different story. I think that by having an understanding of what is necessary and is not necessary, I'll be able to see through the marketing nonsense with TVs. As far as I'm concerned though, 96 dpi from 2ft away definetly leaves alot to be desired. I feel like I'm stuckin my own (1080p sucks) universe while everybody else is like "thank god, ooooooooo thank god!".


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