Resolution

[markc]

If you want to compare them all at the same PPI, then you would have:

3.1 MP = 4.8" x 7.25" @ 300 PPI.
4.1 MP = 5.5" x 8.25" @ 300 PPI.
10.2 MP = 9" x 13.5" @ 300 PPI.

 

[RacePhoto]

If you want to compare them all at the same PPI, then you would have:

3.1 MP = 4.8" x 7.25" @ 300 PPI.
4.1 MP = 5.5" x 8.25" @ 300 PPI.
10.2 MP = 9" x 13.5" @ 300 PPI.

That's what I figured. My old Mavica 7 = 640x480 camera at 300 PPI will produce a 2.13" x 1.6" image size. :thumbup:

Nice if I wanted to print postage stamp size pictures.

 

[e999sam]

Again thanks everyone for the input.
After playing around with the different images I have come to the my own conclusion that dpi/ppi has little effect on the final printed image.
The 72 dpi image from my original post was a jpeg and when opened in Photoshop gave an image size of 31inchs x 23 inches this obviously way to big for 4.1 mega pixel image. If I reduced the image size to around 10 x 8 and increased the ppi to around 240 the file size is approximately the same as the original. So
I think the 72 dpi is just a quirk of the camera software because if I take a raw image with the same camera and convert it using Photoshop I get an image size of 10 x 8 with a ppi of 240.
Hope I have made myself clear.

 

[Alex_B]

Why are the resolutions the same for a 3.1 and 10.2 MP camera but much lower for the 4.1 camera?

because resolution is totally arbitrary ... unless you also include image SIZE, from the same MP digital image you can get any resolution you want if you just vary the size.

 

[EOS_JD]

Again thanks everyone for the input.
After playing around with the different images I have come to the my own conclusion that dpi/ppi has little effect on the final printed image.
The 72 dpi image from my original post was a jpeg and when opened in Photoshop gave an image size of 31inchs x 23 inches this obviously way to big for 4.1 mega pixel image. If I reduced the image size to around 10 x 8 and increased the ppi to around 240 the file size is approximately the same as the original. So
I think the 72 dpi is just a quirk of the camera software because if I take a raw image with the same camera and convert it using Photoshop I get an image size of 10 x 8 with a ppi of 240.
Hope I have made myself clear.

Read my post above again. The resoilution means nothing. When editing images look at the total number of pixels and compare that.

If the print size is 31x23 @72ppi that = 2232 x 1656 pixels.
A 10x8 @ 240ppi = 2400 x 1920 pixels.

 

[EOS_JD]

Debating industry semantics is a waste of time, and only clouding the issue for the original poster. PPI and DPI, when used to determine print size, effectively mean the same thing. If you scan a negative at 300 Dots Per Inch, it becomes a digital file. That digital file, in order to print at 300 Dots Per Inch must be set to 300 Pixels Per Inch in the software. The only confusion is in trying to differentiate between the two, when for all practical purposes, they mean the same thing.

You are doing nothing but adding to the confusion for the original poster.

Pixel dimension / PPI or DPI = Print Size. DPI and/or PPI are irrelevant until you decide to print, in which case you use that formula to determine the dimensions of your file.

OK I realise I'm probably hitting my head against a brick wall a bit here but as I say it's a very simple equation and I'm trying to get people to understand that resolution means nothing.

They really are not the same thing but I accept that they are taken as meaning the same.

Cheers
Jim
PS - To print at 300dpi you don't need a 300ppi image!

 

[EOS_JD]

While all the answers and the discussion was interesting and educational, can anyone answer the question? Why are the resolutions the same for a 3.1 and 10.2 MP camera but much lower for the 4.1 camera?

Is the 4.1 camera 75 PPI producing a much larger overall image, while the 3.1 is a smaller image with more PPI because it's smaller is actual size?

It's the number of pixels in the image that counts. Look at this


D30 is 3.1Mp = 2,160 x 1,440 pixels
1d is 4.1Mp = 2,464 x 1,648 pixels
300D is 6.3Mp = 3072 x 2048 pixels
20D is 8Mp = 3504 x 2336 pixels
400D is 10Mp = 3888 x 2592 pixels

Finally

a 1Ds MkII is 16.7Mp = 4992 x 3328 pixels

these are the number of pixels that these cameras produce. Higher pixel count = more resolution. Divide the pixel dimensions by the print resolution to get the image size.

If you want a 240ppi print you'll get the following (you can divide each pixel count by whatever you like to get the print size.

D30 is 3.1Mp = 2,160 x 1,440 @240ppi = 9" x 6"
1d is 4.1Mp = 2,464 x 1,648 @ 240ppi = 10.26667" x 6.86667"
300D is 6.3Mp = 3072 x 2048 @ 240ppi = 12.8" x 8.5333"
20D is 8Mp = 3504 x 2336 @ 240ppi = 14.6" x 9.7333"
400D is 10Mp = 3888 x 2592 @ 240ppi = 16.2" x 10.8"

Finally

a 1Ds MkII is 16.7Mp = 4992 x 3328 @240ppi = 20.8" x 13.8667

Does this make any sense to you?

 

[EOS_JD]

Assuming a 2:3 ratio...

3.1 MP = roughly 1450 x 2175 pixels. At 230 PPI, that's a 6.3" x 9.5" print.
4.1 MP = roughly 1650 x 2475 pixels. At 75 PPI, that's a 22" x 33" print.
10.2 MP = roughly 2700 x 4050 pixels. At 240 PPI, that's a 11.25" x 16.9" print.

To do a real comparison, we need all the same print size or all the same PPI number. Let's say a 8"x12" print size.

At 8" x 12" print, a 3.1 MP image is about 181 PPI.
At 8" x 12" print, a 4.1 MP image is about 206 PPI.
At 8" x 12" print, a 10.2 MP image is about 338 PPI.

Now you can make an accurate comparison between the PPI (DPI) numbers, and higher means more quality. But that's only because the print sizes (in inches) are the same. You could also use 4"x6" if you wanted to, but all three would need to be figured at 4"x6".

Note that at the original numbers, the 10.2 MP camera gives you a much bigger print at the same PPI than the 3.1 MP camera does. This shows that it's the number of pixels that drive the quality, not just the PPI number.

Sorry Mark - Just noticed you did something similar. You are correct in all that you write. the ppi has no effect on the digital images quality. Only pixels count.

When you come to print, the number of pixels divided by the required resolution will determine print size and quality of likely output.

 

[Digital Matt]

PS - To print at 300dpi you don't need a 300ppi image!

No, but you need to know that your dimenesions will give you the size image you want at 300 DPI, and the easiest way to ensure that is to set the PPI of the image to 300 in photoshop, and see for yourself. I already know that a 1200x1800 will give me a 4x6 at 300 DPI. For most people though, it's easier to see a graphical representation of this. If I'm resizing a photo in photoshop, I'm not going to open calculator to figure out how big I need to make it for a 56 x84" print at 300 dpi. I'm going to change the PPI to 300, and set my pixel resolution accordingly, and I know I'll get a subsequent image that will print 56" x 84" at 300 DPI.

 

[Alex_B]

For most people though, it's easier to see a graphical representation of this. If I'm resizing a photo in photoshop, I'm not going to open calculator to figure out how big I need to make it for a 56 x84" print at 300 dpi. I'm going to change the PPI to 300, and set my pixel resolution accordingly, and I know I'll get a subsequent image that will print 56" x 84" at 300 DPI.

true,
but most people stumble over this whole dpi issue way too early, long time before they are going to print anything or even considered printing. in my experience that is part of the problem. some camera and some software and some file formats talk DPI to people long before it matters to them in any way... no wonder that they are confused then.

from my experience, once people start seriously thinking about printing things, then they start to understand the dpi concept anyway


this is just my experience from discussing with people ...

 

[EOS_JD]

No, but you need to know that your dimenesions will give you the size image you want at 300 DPI, and the easiest way to ensure that is to set the PPI of the image to 300 in photoshop, and see for yourself. I already know that a 1200x1800 will give me a 4x6 at 300 DPI. For most people though, it's easier to see a graphical representation of this. If I'm resizing a photo in photoshop, I'm not going to open calculator to figure out how big I need to make it for a 56 x84" print at 300 dpi. I'm going to change the PPI to 300, and set my pixel resolution accordingly, and I know I'll get a subsequent image that will print 56" x 84" at 300 DPI.

What I was getting at is I can print my 6 x 4 @300ppi on my printer at 5760dpi. That's the difference in dpi and ppi.