Increase image size, affect image quality as little as poss

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PMK

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I'm sure it's pretty simple - but I rarely print my work and want to start: how I can increase the image size, without reducing too much of the quality of the image.

E.g - Flickr has the ability to do this automatically (once uploaded they provide different sizes - even the largest image is pretty good). It's something I'd like to replicate. Using Photoshop preferably.

Thanks in advance.
 
How large do you want to print?

I have printed up to A3+ straight from the camera from my old D70 (6.1MP) and the results look pretty damn good from normal viewing distance. It might be possible to see pixelation under magnification but who does that in real life?
 
Are you planning on printing at home?

If you want to use a lab to machine print your work, and you want to preserve much of the quality of your original image, you'll need roughly 250 ppi. You can get really acceptable images at less than that. The D40's images are 3000x2000 pixels.

12x18 is a nice size for many amateurs, in my opinion, so you'd like to have close to 4500 pixels on the longest side. 16 megapixels is ideal for a camera, unless you're into very detailed editing.

So, you could upsize your images in software to get a better result. But some will tell you to try at the native size first and see what the results are like. Some labs may use equipment that maps the images up to better suit a size that's far from the ppi ideal. Home printers can do well at that too I believe, but I only get lab prints done myself.
 
A friend has a printer they have offered, but I was considering Snappy Snaps.

But if I change the image size in PS to 12x18 the quality rapidly reduces? Whereas, in Flickr - with the same image, and increase - it looks fine.

Maybe it's a case of experimenting with what I currently have available to me - I do need to upgrade my camera, but things are a little precarious for me at the moment.
 
What PS version are you using?
How are you resizing - Can you go through each step and say what you are doing?
 
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okay, I'm confused by this question a little

the thing you have to get your head around is
DPI when printing (75dpi might be okay for a large canvas but for a smaller photo you need a higher DPI (250-300dpi maybe) because you'll see the item close up.

PPI when displaying on screen depends upon how many pixels there are your monitor of a certain size.

and ultimately it's down to resolution.

a recent example for me:
An image was supplied to me at 1800 pixels by 1200 pixels
so printing at 300DPI that gives me a lovely 6" x 4" image.
if I printed it out at 10" x 6" it would be around 200dpi (give or take)
still okay but not as highly detailed. But if it's being viewed with less scrutiny, then you can get away with it. The smaller the print the more people will look up close imho

FlickR take an image of a certain size and then reduce it I think
they don't take one and the blow it up, somehow retaining it's quality.
Happy to be wrong here btw.
but if you can, always start with the largest image size available, and work from there.
Too much detail is fine as that can be just lost in the printing process as the hardware & software scales it to the media size.

Too little detail and it isn't recovered, as much as interpolated so a single pixel is made to cover a larger range, or the computer takes two pixels, spaces them apart and then guesses as best it can would might be between them

remember, and people will disagree with me on this...but DPI is NOT an image size. it's a ratio. to give it any meaning you need
for example if you say you're travelling at 60 mph and you want to get there in an hour....fine...but it means nothing until you know your distance travelled.

here are some examples from the t'interweb
I havent' read them in detail but I think they cover the same thing
http://www.geniusprinting.com.au/howbig.php
http://www.photobookgirl.com/blog/w...n-or-dpi-for-photos-when-making-a-photo-book/
 
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PMK said:
CS4

Open the image > make any amendments (this is usually only a little bit of level balance, slight cropping).

Image > Image Size

Then amend the document size.
Click to expand...

Can you say what numbers are in all the boxes before you amend the document size and what they are after?
Also what option boxes have you got ticked?
 
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PMK, it's also worth doing an experiment or 2. Firstly, take an unresized file to your friend with the printer and run off a print. Now look at the print from a normal viewing distance. What do you and your friend think of the result? An unresized file from your D40 is (IIRC) 3000px x 2000px, giving an 18" x 12" resolution of 166.666666 dpi. Now try reducing that even further - say to 100dpi, then further still 75dpi maybe. By now, you may start to see a significant reduction in quality (on photo quality papers) but on other media (canvases for example) you'll get away with far lower resolution than you will on photographic paper.

For photos, the normal viewing distance is often quoted as being 1.5x the diagonal dimension of the print, so for that 18x12, about 33". A 6x4's NVD would be around 11".

If you do need to upsize your files, I've read that it's best to do so in PhotoShop in smallish increments rather than one large step. Using specialist upsizing software (whose name escapes me at the moment), you can do it in one step and the results are supposed to be superior to PS's.
 
Expanding a 3000x2000px image can never be as good as starting with a larger one in the first place. The 300dpi figure is a standard for magazine reproduction (among others) and is a point above which it's fairly pointless to go. You can easily get away with smaller for the real world - try it, you'll be surprised! If you're determined to stick to 300dpi, you'll have to be satisfied with 10" x 6 2/3" or interpolate which adds averaged pixels between actual ones so reduces ultimate quality.
 
At a 10" x 6 2/3" print size, a 3000px x 2000px image will be 300dpi. Screen resolutions vary but seem to be around 72ppi (note the difference between pixels per inch and dots per inch). If the 18x12 print isn't up to scratch, try an A4 print (slightly larger than your optimum 10x6 2/3). What you can get away with is dependent on the printer and paper as much as the image size (in pixels), there are obviously limits (for example a 3MP image isn't quite enough to go up to A4) but a smaller file will print surprisingly large. Look at billboards - close up, they're a mess of what appear to be random dots but step back a few yards and the image appears as if by magic. Some of them were shot with less than your 6MP!
 
Nod said:
Expanding a 3000x2000px image can never be as good as starting with a larger one in the first place. The 300dpi figure is a standard for magazine reproduction (among others) and is a point above which it's fairly pointless to go. You can easily get away with smaller for the real world - try it, you'll be surprised! If you're determined to stick to 300dpi, you'll have to be satisfied with 10" x 6 2/3" or interpolate which adds averaged pixels between actual ones so reduces ultimate quality.
Click to expand...

Interpolated pixels aren't averaged. You use a very complex filter.

Scaling is best done to multiples of pixels, not just random sizes.
 
Guys I think you're getting way too advance here.

To the OP, you need to separate thinking about the resolution and the DPI. Any size image can have any DPI. Talking about megapixel counts is also pretty unhelpful as the shape of the image matters with that too.

So what you need to establish is the size of you image in pixels. Assuming 3000x2000 here. Now if you printed that at 300DPI every line 300 pixels long will be a line 1 inch long on the print. Now if you print the same image at 100DPi that 300 pixel line is now 3 inches long.

So you can alter DPI to make the print size bigger, or you can resize the image to a physically larger size and print at 300dpi. You're unlikely to see the difference in prints whichever method you do, although if you resize it yourself then you can perform some additional processing if you wish that can alter the appearance, such as smoothing over less detailed areas etc.

Remember to change the resize mode when you do this. Photoshop doesn't give you a lot of options to work with, Paint Shop Pro gives you much finer control of this but most of the time you won't need it.
 
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