image size

[Bionic Modeler]

When an image size is shown as 2540 x 3480 what exactly does that mean. Does this indicate the original paper size it was scanned from?

[peter taft]

Either the original scanned size or even a re-size of an image. The size you stated is quite large, especially compared to a 640 X 480.

[peter taft]

This might help with sizing and aspect ratio !

720x480-----3:2
1152x768-----3:2
1280x854-----3:2
1440x960-----3:2
2880x1920----3:2

___________________

320x240-----4:3
640x480-----4:3
800x600-----4:3
1024x768-----4:3
1152x864-----4:3
1280x960-----4:3
1400x1050-----4:3
1600x1200-----4:3
2048x1536-----4:3
3200x2400-----4:3
4000x3000-----4:3
6400x4800-----4:3

___________________

800x480-----5:3
1280x768-----5:3

___________________

1280x1024-----5:4
2560x2048-----5:4
5120x4096-----5:4

___________________

852x480-----16:9
1280x720-----16:9
1365x768-----16:9
1600x900-----16:9
1920x1080-----16:9

___________________

320x200-----16:10
640x400-----16:10
1280x800-----16:10
1440x900-----16:10
1680x1050-----16:10
1920x1200-----16:10
2560x1600-----16:10
3840x2400-----16:10
7680x4800-----16:10

___________________

2048x1080-----17:9

[Bionic Modeler]

except I don't know what aspect ratio is either. Sorry for being so dumb

[peter taft]

Look at a normal TV and you have a ratio of 4:3 that's 4 X Horizontal to 3 X Vertical - if this was a sheet of paper it would be almost square, a wide screen TV with 16:9 ratio in paper terms would be an image in landscape.

[peter taft]

Tim... you may find this handy !

Aspect Ratio Calculator (ARC)

[sgoti]

Originally Posted by Bionic Modeler

When an image size is shown as 2540 x 3480 what exactly does that mean. Does this indicate the original paper size it was scanned from?

It simply means the size of the digital image in pixels. In this case 2540 pixels wide and 3480 pixels high.

It does not necessarily translate into the original paper size it was scanned from. An 8.5 x 11 inch image at 300 dpi would have a pixel size of 2550 X 3300, but the same paper scanned at 72 dpi would have a pixel size of 612 x 792.

[airdave]

Originally Posted by Bionic Modeler

When an image size is shown as 2540 x 3480 what exactly does that mean. Does this indicate the original paper size it was scanned from?

The number means nothing in the real world unless you know the dpi.

Have you ever had to set your desktop resolution? to something like 1024x768
You are setting your screen to show a certain number of dots in a certain area.
The higher the numbers, the more dots (pixels) will be shown on the screen.

So its important to know the resolution first if you want to relate a pixel size,
like 2540 x 3480, to a sheet of paper.
The resolution is measured in dots per inch (dpi)

The higher the dpi number, the more dots of information, which equals a
higher resolution (quality) image.

So, if you know the image is 300dpi, then you can work out that the printed
size will be about 8 inches horizontally (2540 divided by 300 equals 8.4)
and about 11 inches vertically.

Note: for artwork, 300 dpi is an acceptable resolution.
For a photograph, 300 dpi would be very low quality.

Aspect ratio is the ratio between the horizontal and the vertical.
Think about your old TV versus your new widescreen TV.

[Bionic Modeler]

Thanks all for your help. Now I understand it better. I wanted to know becasue i never know how large I can print something without going beyond what it was intended to be. That calculator will donicely. Thanks again

[cfuruti]

Originally Posted by airdave

The number means nothing in the real world unless you know the dpi.
...
The resolution is measured in dots per inch (dpi)

The higher the dpi number, the more dots of information, which equals a
higher resolution (quality) image.

So, if you know the image is 300dpi, then you can work out that the printed
size will be about 8 inches horizontally (2540 divided by 300 equals 8.4)
and about 11 inches vertically.
...

Agreed with Airdave and Sgoti, with some additional caveats:

1. sometimes higher DPI doesn't mean better quality. Both cheap digital cameras and some scanners may interpolate pixels artificially boosting resolution without adding any new information and sometimes actually degrading quality
2. by the same token, if one simply opens an image in a raster editor like Paint or the GIMP and saves it in a bigger size, the result won't have better quality and might look blurry. For some purposes, like image restoration, this could have some utility. Don't confuse this with anti-aliasing by downsampling, where the original image is generated with higher resolution then reduced for the final result
3. it's well known that if two digital cameras have CCDs with similar physical size but different resolutions, the higher-res one will usually have worse image quality because each physical pixel will be smaller, receive less photons, be forced to use higher amplification and therefore be subjected to more electronic noise. This does not take into account lens quality and in-camera noise-reduction software
4. obviously, actual print size is also dependent on resolution

One of the biggest benefits of structured vector formats like SVG and PDF is that they include resolution information, therefore no matter where you show or print them, the size will be consistent; 1 cm on screen, 1 cm on paper, unless your system is badly calibrated. In other words, you worry about the resolution just twice: when you create or set properties for the documents, and when you import a raster into it*. For raster formats like JPG, you must worry whenever you print them.

*ok, I cheated. You also worry if and when you want to convert to raster.