Megapixel vs print size


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merkava74

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#1
I have a question:

If I have a 6mp camera, I was told that the largest output size is A3.

But why is it that when I go to photoshop to make an A4 canvas, and then I drag my photos over, they cannot even fill up the A4? I had to scale and stretch it to fill it up.

Will I lose resolution? And why does this happen in the first place, when 6MP is supposed to give me A3?

Appreciate some clarity, please.. Thanks!
 

Ah Pao

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#2
6MP at A3, but at what resolution? What's the DPI (dots per inch) resolution of your A4 canvas?
It's actually quite pointless to talk about image dimensions and print size without the resolution - one of the 3 variables are missing.

If you are printing at 300 dpi, then your 3072 x 2048 (6MP) file will occupy at 10.24" x 6.83" which is smaller than a piece of A4 paper. If you are printing at 150 dpi (most photo labs' resolution, IIRC), then it will be double that size.
 

merkava74

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#3
Ahhh.... my A4 canvas was set at 300dpi, same as my image.

Now, would the picture still be as clear if I reduce the canvas to 150dpi?

You said that photo labs are set at 150dpi? In other words, I have been redundantly setting it too high when in fact the printer can print the same detail at 150?
 

d7t3

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#4
if you go to the various labs' websites, you'll see some minimum figures for prints. if you work it out, some are as low as the 150ppi (pixels per inch) region. some even lower.

additional info: the ppi requirements depend on the printing technology. the standard inkjet figure is 300ppi, but some epsons have had 240ppi as their 'base'. for dye-subs and commercial minilabs, the figure is lower.

printing dpi (dots per inch) is not exactly the same. let's say the printer has 1440dpi. if you give it a 240ppi image, it will print 1440/240 = 6 ink dots per image pixel.
 

mastermind

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Just count the dots. 6mp = 6,000,000 pixels. While print quality of 300dpi means 300 dots per inch. A4 size = 297mm by 210mm or roughly 8,700,000 dots. If 1 pixel is 1 dot in your print, then you need 8.7mp for a borderless A4 print.

Of course, 1 dot may not be the same as 1 pixel as some interpolation/extrapolation may take place and the horizontal dots may not be the same as vertical dots. In fact my HP printer can do up to 2400 x 1200 dpi prints (how the heck they do it)

There's much science involved here and I guess only the engineers can explain the details.

It gets depressing to know that for all the megapixels we are getting, we can't really print large high quality photos.
 

ob1canob

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mastermind said:
Just count the dots. 6mp = 6,000,000 pixels. While print quality of 300dpi means 300 dots per inch. A4 size = 297mm by 210mm or roughly 8,700,000 dots. If 1 pixel is 1 dot in your print, then you need 8.7mp for a borderless A4 print.

Of course, 1 dot may not be the same as 1 pixel as some interpolation/extrapolation may take place and the horizontal dots may not be the same as vertical dots. In fact my HP printer can do up to 2400 x 1200 dpi prints (how the heck they do it)

There's much science involved here and I guess only the engineers can explain the details.

It gets depressing to know that for all the megapixels we are getting, we can't really print large high quality photos.
Sorry for my mistake earlier.
 

mpenza

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#7
Ah Pao said:
If you are printing at 300 dpi, then your 3072 x 2048 (6MP) file will occupy at 10.24" x 6.83" which is smaller than a piece of A4 paper. If you are printing at 150 dpi (most photo labs' resolution, IIRC), then it will be double that size.
actually if u print at 150dpi, it'll be 4 times the size (area), not double.
 

loudhailer

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merkava74 said:
Ahhh.... my A4 canvas was set at 300dpi, same as my image.

Now, would the picture still be as clear if I reduce the canvas to 150dpi?

You said that photo labs are set at 150dpi? In other words, I have been redundantly setting it too high when in fact the printer can print the same detail at 150?
let me try to answer ur qn.

A4 canvas at 300dpi....its 8.27" X 11.67"....which equals 2481 X 3501.
Your 6MP DC produces a 2000 X 3000 image.
So your image straight out of the DC is already smaller than the canvas.

usually the photolabs print at 150dpi AFAIK...or maybe the photolab that i send my pix to uses 150dpi. the extra pixels are used for downsampling the pix to 150dpi just before printing by the photolab. this is done by the photolab.

printing a 150dpi or 300dpi image at 150dpi should be the same, subjected the downsampling algorithm used.
 

#9
6.0MP can print very clear at A3 i have done it many times, dunno what the resolution was, but its crystal sharp no pixilation at a native size of 3000X2000, so therefore A4 and A3 no problem unless you have cropped too much past the 3000X2000 mark.
 

roti_prata

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#10
wildstallion said:
6.0MP can print very clear at A3 i have done it many times, dunno what the resolution was, but its crystal sharp no pixilation at a native size of 3000X2000, so therefore A4 and A3 no problem unless you have cropped too much.
consumer or pro? got diff 1.
 

wind30

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this kind of question is VERY SUBJECTIVE. There is only one answer, take a 6meg file and print it whatever size you want. Or find a similar size print made from a 6meg file and view it. Different people has VASTLY different standards for sharpness.

Some view a A3 print 5 cm away from their nose...

oh an megapixel does not equal to resolution. not every pixel are created equal. Depends on the lens, lighting. So to judge whether 6meg is enough, make sure that the 6meg file is taken with a SHARP lens, under good lighting.
 

merkava74

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#13
Thanks for all the various perspectives.

Actually, the question assumes a few things constant:

1. Image clarity
2. D70s at jpeg fine 3008 x 2000
3. Paper quality
4. Printer quality

The output from the camera is at 300dpi. If I set the A4 canvas at 300dpi, the image does not fill the page.

So, don't even have to think about 300dpi at A3 size...

The question is, if I were to print A4 at 150dpi, does image quality degrade? I assume yes. By how much? I assume 100%? Since now it takes 2 pixels to form the same line (assuming line is 1 pixel)...

But having said all that, I am led to think that the difference when printed is not visible to the naked eye, unless seen from close...

Care to verify the above statements? Would be good if some could post some pics as example...
 

#14
merkava74 said:
Thanks for all the various perspectives.

Actually, the question assumes a few things constant:

1. Image clarity
2. D70s at jpeg fine 3008 x 2000
3. Paper quality
4. Printer quality

The output from the camera is at 300dpi. If I set the A4 canvas at 300dpi, the image does not fill the page.

So, don't even have to think about 300dpi at A3 size...

The question is, if I were to print A4 at 150dpi, does image quality degrade? I assume yes. By how much? I assume 100%? Since now it takes 2 pixels to form the same line (assuming line is 1 pixel)...

But having said all that, I am led to think that the difference when printed is not visible to the naked eye, unless seen from close...

Care to verify the above statements? Would be good if some could post some pics as example...

why would the quality degrade? A4 is smaller than A3, quality would be better right?
 

d7t3

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#16
1. the output from a digital camera is pixels, not dpi. dpi can be changed without changing the image at all.

2. it depends on the printer you use. some inkjets require 300dpi, some commercial minilabs only require 150. so if you print 150 dpi on an inkjet, it will look worse than 150 on a minilab.

3. my wife won a prize in a competition and the organisation blew up the winning entry (taken with d70) to something like A2. from a jpeg.

4. how can we post pics to show print quality???
 

merkava74

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#17
d7t3 said:
1. the output from a digital camera is pixels, not dpi. dpi can be changed without changing the image at all.
I know that... it's fine on the pc, but changing dpi definitely changes print quality, which is what I was try to find out: by how much...

d7t3 said:
2. it depends on the printer you use. some inkjets require 300dpi, some commercial minilabs only require 150. so if you print 150 dpi on an inkjet, it will look worse than 150 on a minilab.
Thanks. Now I know.

d7t3 said:
3. my wife won a prize in a competition and the organisation blew up the winning entry (taken with d70) to something like A2. from a jpeg.
They go through another process (drum scanning) to get A2 from a 6MP. print the jpeg at highest quality, drum scan it, then reprint at much higher resolution. Not possible straight from jpeg.

d7t3 said:
4. how can we post pics to show print quality???
What I meant was if someone was willing to go through the trouble of printing in both 300 and 150 dpi, and then rescan them equally, post it and see the diff. But I guess that's too much trouble.
Thanks for your reply anyway.
 

zoossh

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#18
newbie here. newbie method, dunno works for y'alls or not.

mine is nikon D50, shot at raw 3008x2000 pixels. i open the raw on adobe photoshop and default dots per pixel is 300. then i alt-I-R-I to go under image, resize, image size. then i will change the DPI but maintain the same no. of pixels so that the actual print size will change to the size i want.

i routinely goes to word document to see what's the size of the ISO i want. after a while familiar with A4 size is 210mm x 297mm, so i will try to change the DPI at the same pixel size of 3008x2000 to reach the size i want, for example, A4 210x297mm.

wonder if that works?
 

Ah Pao

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#19
merkava74 said:
I know that... it's fine on the pc, but changing dpi definitely changes print quality, which is what I was try to find out: by how much...
Really, it's a subjective judgement and you have to decide whether you are willing to accept the loss of quality. And this again will depend on the output device and the final application of the output, as written in the posts above. Do a simulation with Photoshop if you want - play with the image size and DPI settings.

They go through another process (drum scanning) to get A2 from a 6MP. print the jpeg at highest quality, drum scan it, then reprint at much higher resolution. Not possible straight from jpeg.
Nope, it doesn't quite work that way.

There's only so much information in the original image; it doesn't matter if you printed it out and then drum scan it or if you do a direct file-to-print. Whatever "extra" data that comes out from the scanning are extrapolated and not extracted from the original file.

Commerical printers do drum scanning to digitise prints and slides at high resolution, not to enlarge them. It's like cutting a piece of square cake into 2 x 2 vs 4 x 4, 8 x 8, 16 x 16...but the amount of cake doesn't change.

And so it depends on the application. As wind30 said, some may view an A3 poster 5cm away, but the sane majority won't do that.
 

#20
Ah Pao said:
And so it depends on the application. As wind30 said, some may view an A3 poster 5cm away, but the sane majority won't do that.
I can view my A3 from 30cm to 5m quality looks nearly identicle to me, i seriously think no problem printing 3008x2000 at A3, quality is fine, but if your not sure just go have some prints done, its only going to cost like $15, print one at A4 and one at A3 size, then you will know what the quality is like!!!
 

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