Enlarging digital photos

[Steviekid]

If I took a photo with a 7 megapixel camera, roughly how big could it be enlarged before it started to look cack?

[AndyT]

At least A4 bud. Probably more.

[Steviekid]

At least A4 bud. Probably more.

 

Ah, I was hoping it would be more like A1! Shows how much I know about this sort of thing!!

[michael]

At 300dpi (magazine quality) you'd be looking at something like 20x30cm / 7x10" at 3000x2000 resolution.

 

You could go bigger and the pic would still be fairly acceptable to most human eyes.

 

Edit, this might be of interest...

 

First - Most cameras are not exactly 3, 4, 5, etc megapixels.

So you want to look at the Maximum Resolution.

The camera maker may state that max resolution for a 3 megapixel

camera is 2048 x 1536.

 

That means 2048 pixels x 1536 pixels

 

When you print a photo, you talk about dpi (dots per inch).

A printer set to print at 300 dpi will produce an excellent photo.

A printer set to print at 150 dpi will produce very good photos.

 

For this exercise you relate pixels and dpi as being the same thing.

 

Divide 2048 by 300 = 6.8 inches

Divide 1536 by 300 = 5.12 inches.

 

So you will get an excellent 6.8 x 5.12 inch print if you printer is set for 300 dpi.

 

....................................

 

Working backward - you want an excellent 8 x 10 photo.

 

That is a problem because that is a ratio of 4 x 5 (width to length ratio)

You digital camera most likely will produce a 3 x 4 ratio.

 

That means you will have to crop the picture to create a 4 x 5 ratio result.

If you don’t want to crop, you have to accept a 7.5 x 10 inch or 8 x 10.67 inch photo.

 

Lets choose the 7.5 x 10 inch photo.

 

Multiply each number by 300 and you get 2250 x 3000 (or 3000 x 2250).

So you need a camera that has a maximum resolution of 3000 x 2250

 

A six megapixel camera is 2816 x 2112

An eight megapixel camera is 3264 x 2448

 

So my guess is, you would need a seven megapixel camera (minimum), but I don’t think anyone makes a seven megapixel camera.

 

...........................................................................

 

But reality is a bit more squishey that that:

 

Lets say you have a 3 megapixel camera - 2048 x1536 maximum resolution.

Now let us use Photoshop or some other digital photo manipulation software,

and resize/resample that 2048 x 1536 photo to a size of 3264 x 2448.

 

After you resize/resample the photo, you then use a software tool (unsharp-mask) to sharpen the photo.

 

You now have a photo file that you can print at 300 dpi and get an excellent 7.5 x 10 inch photo.

 

From http://forums.cnet.com/5208-7593_102-0.html?forumID=58&threadID=26876&messageID=301967

[Steviekid]

Cheers for that

[AndyT]

Very nice Michael. Thanks for the info too.

[colsoop]

I have enlarged some digi pics to 30 x 40 cm and they came out very good. (Max quality on a canon eos 350 d)

 

Michaels answer is comprehensive but this link is from a company who print photos and gives an idea of what is needed for certain sizes:

 

http://www.photobox.co.uk/static/resolution_guide.html

[PJ]

If you want to blow a picture up to poster size or larger you could always Rasterbate it, then print it out on multiple sheets and stick it all back together, can look kind of funky and you can go to huge sizes. Probably not what you are looking for but can be quite fun.

 

http://homokaasu.org/rasterbator/

 

I think you can blow up an image to 20 metres or something like that.