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Old Mar 18, 2006, 10:57 AM   #1
Log
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When it comes to megapixels i can never quite understand how big they can be blown up. Does anyone know how large pictures can be blown up for 6,7,8,9, & 10 megapixel pictures without distortion? thanks
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Old Mar 18, 2006, 11:16 AM   #2
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Log wrote:
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When it comes to megapixels i can never quite understand how big they can be blown up. Does anyone know how large pictures can be blown up for 6,7,8,9, & 10 megapixel pictures without distortion? thanks
The real question is NOT how large they can be blown up without distortion - but rather how large can they be blown up to retain detail.

I have printed 16 x 20's of landscapes from a two meg sensor with stunning results. This is accomplished by using the "interpolation" feature of most image processing programs.

In other words, this was originally a 6 meg plus TIF file, interpolated up to 100 megs. Interpolation does not create detail, but it allows existing detail to be enlarged without the "jaggies."

The same technique on a close-up portrait would NOT be successful unless viewed from a large distance. It would look "fuzzy."

Dave

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Old Mar 19, 2006, 6:06 AM   #3
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A rule of thumb is to look at the pixel dimensions and aim for 300DPI so a 6Mp camera would be about 3000 x 2000 pixels whitch gives roughly 10x7 inches. However you can usually get away with 200 DPI so that becomes 15x10 inches.

As Dave say interpolation helps and also larger prints are usually viewed from further away so you can get away with even less real detail.

I project pictures using an 800 x 600 digital project up to about 4ft across. Close up the pixels look like bricks but from a normal viewing distance the result is fine. That equates to 4ft by 3ft from 0.5Mp projector.

So for normal print sizes say up to A4 a 2 or 3Mp camera is probably fine but more will give a better result and allow for more cropping while still retaining a printable result.

It's also worth bearing in mind that MP is a measure of area not a linear measure. For example a 3Mp camera is 2000 x 1500 and 6Mp is 3000 x 2000 so using 300 DPI as a guide you can print 3Mp to 7 x 5 not 5 x 3.5 as you might expect.
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Old Mar 20, 2006, 5:54 PM   #4
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ok I have been waiting to ask....what is A4...? is there any other paper size lingo that I should know about?
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Old Mar 20, 2006, 7:26 PM   #5
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It also depends on how many details are in the picture. For example portaits of faces can be blown up larger than an intricate landscape with detailed rocks, blades of grass, leaves and such.

For simple PPI calculations I have a calculator on my website (www.mattspinelli.com) that will show how a given camera of a certain MP rating will print. The math is simple but my calculator shows all the sizes at once and you may find it helpful in this pursuit. It also will allow you to compare cameras and see the differences in their PPI output for given sizes.
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Old Mar 21, 2006, 3:34 AM   #6
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dashboardgyno wrote:
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ok I have been waiting to ask....what is A4...? is there any other paper size lingo that I should know about?

It's a metric paper size 8.3 x 11.7 inches 210 x 297 mm. A3 is double A4 at 410 x 297 mm.
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Old Mar 21, 2006, 9:23 AM   #7
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If an image looks really good on a computer screen at 75 DPI, then why does it need 300 DPI when printed ?

Maybe 75DPI is a little low, but what would be wrong with 100 or 150 DPI ?
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Old Mar 21, 2006, 12:13 PM   #8
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me2 wrote:
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If an image looks really good on a computer screen at 75 DPI, then why does it need 300 DPI when printed ?

Maybe 75DPI is a little low, but what would be wrong with 100 or 150 DPI ?
This is because a printout involves 4 colors trying to fool the eye into seeing the entire gamut of color. Your computer screen is actually displaying ppi, not dpi. In other words, try to picture your printed image as 75 little squares, each being a seperate color. Now try to simulate these colors with your four color (or even six or eight) color printers?

Your monitor of course DOES display 16 million plus colors...

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Old Mar 21, 2006, 2:58 PM   #9
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Dave, while sort of plausible your explanation doesn't quite ring true. Firstly my monitor only display 3 colours Red Green and Blue and mixes these to fool my eye into seeing 16 million colours. This works because my eyes are only actually sensitive to three colours Red Green and Blue which my brain mixes and interprets as the whole spectrum. My printer on the other hand prints in three colours Yellow, Cyan and Magenta the complimentary colours to Red, Green and Blue plus of course the white paper and a black ink. My printer is 5760 DPI so each of the 300 dots of my image is made up of a mix of up to 28 individual dots of ink.

That said I don't have a better explanation and a 75 DPI print is not the same a monitor display.

Mind you I have a problem with the idea that the monitor is 75 DPI or 72 DPI. If I have a monitor that is 1024 x 768 pixels is that a 12 inch screen a 14 inch screen a 17 inch screen? There's no way they can all be the same DPI.


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Old Mar 21, 2006, 4:38 PM   #10
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What I think people are talking about is the use of 72DPI (not 75DPI) and how it relates to TV (I think its TV, not movies.)

That value has abosolutely no effect on how the picture is displayed on your monitor. It is flat-out ignored. You can change the DPI and nothing will happen to the image on screen.

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