[raider]

Hi,

Quick question re. the dpi setting of photos.

I know the equation and relationship between photo resolutions and dpi. The question is, what sort of dpi should i at least achieve for submission to a photo competition? 300dpi? 200dpi? 150dpi?

Obviously 300dpi will give the best quality but this also make the actual print size a lot smaller. For instance, my K-7 can only yield 15" x 10" at 300dpi. If i go with say 200dpi, would i lose a lot of quality?

Opinions please?

Many thanks
raider

[Marc Sabatella]

If you know the relationship, then you know the dpi setting you choose is irrelevant,. Al that matters is the number of pixels. If you submit an image with a given number of pixels and they print it at a given size, the dpi *will be*given by the formula # pixels / print size, regardless of what dpi setting you put in the Exif header.

So the answer is, given them the number of pixels they ask for, and don't worry about the dpi setting, because it won't matter as long as it is the right number of pixels. If they don't tell you how many pixels they want (most do, in my experience), then give them all you've got.

[hcarvalhoalves]

The DPI only controls the output (print), so if you will be submitting a file it doesn't matter. Either if it gets printed to 72, 150 or 300 DPI, your file will still have the same amount of pixels (true information) in it - for a K-7, 14.6 megapixels. As such, the only parameter that affects which DPI should be used is the size you expect it to be printed. Higher DPI for smaller prints - and vice-versa.

All About Digital Photos - The Myth of DPI

EDIT: Marc beat me to it!

[cats_five]

One assumes you are submitting a print. Some printers give a better result with particular resolution files - read the printer's documentation to see if yours does.

A quick look at your Flickr photostream suggests you are using the SilkyPix software. I have no idea how good that is at resampling. I use Photoshop, once I've cropped as I want, then I resize (if I am going to print) to the correct size to fit A4 or A3 paper (I will have borders, unless the aspect ratio matches I will have a bigger border one side or the other) and it does a very good job of interpolating to give me the correct number of pixels.

The long and short of it is that you need to experiment. You also need to think about how you are going to present your print, and personally I wouldn't dream of printing borders for a comp like you have in your photostream - indeed, they would disallow the print for many comps as they identify you. Read the rules carefully - make your you present your print as they want. Maybe just the print will do, maybe it has to be mounted. If it has to be mounted I imagine there is a maximum mount size and I would go for the maximum. My own photos I surface mount, if you have the kit and ability to cut a window mount that looks far better.

[raider]

Thanks for all the feedback.

I am indeed submitting a print but they only tell me that the board size for the display must be 50cm x 40cm and it is up to me to submit a photo that fit this board size. So i can submit something as small as 10 x 8 for instance and up to the max board size.

Say if i do want to submit a photo as large as 50cm x 40cm, i will be looking at a photo something in the order of 20" x 16".

Assuming my understanding is correct (i am not sure now after all your feedbacks as my understanding could be all wrong), and assuming i did not crop my k-7 output, the result dpi if i ask the printshop to print will be 4672 pixels / 20 = 233.6 dpi. is this correct?

if so, this is less than the optimum and desirable 300dpi, is it not?

So if my understanding is also correct, if i really do want a 300dpi print and i want to print 20" x 16", my horizontal resolution would at least need to be 20 x 300 = 6000 pixels. This is also more than the megapixel count of the k-7.

[cats_five]

You don't want the photo to be too big. And 50cm x 40cm is almost exactly 20" x 16".

However an A4 print looks fine on that size board, so long as it's a good print of course. Tor the metrically challenege, A4 = 8.27" x 11.69".

But, I say again, the photo is best smaller than the mount. Quite a bit smaller. You will probably have pixels to spare unless you have done a lot of cropping. When they say 'a photo that fits the board' I suspect they are telling you that is the maximum size, not the required size.

For a competiton, you need to be prepared to make several prints - I hope you are doing your own printing. That lets you experiment with different dpi, and also look at different size prints on the mount board. The board is not only to stiffen it but to present it as well.

I do know that back in the days of the wet darkroom and B&W prints some people at least used to print onto a piece of 20x16 paper including the borders - the reason was that way the border was bound to tone with the highlights or lowlights in the print. But if you are doing a colour print, an off-white mount will probably work best.

I say yet again, it is more than fine for the photo to be smaller than the board. If you get the chance to see some previous competition entries before handing in that might help.

[raider]

Thanks for the helpful comment again, esp in regards to the image size.

Yes. I will not be printing 20" x 16" but was just referring that as an example. I will print much smaller in fact.

The thing is, i really do not know what size of an image to print which is the reason i am toying with using 300dpi as the benchmark to determine the print size. That 300dpi the way i understand it will end up with a print from the k-7 of 15" x 10" or so.

Is this a good size for the 50x40 board? this is a little bigger than the A4 size that u quoted.

Unfortunately i dont have a large format printer at home and so i have to bring this to a photolab and the one i went to at least have the decency to tell me that their printers are colour cailbrated to their screens and so i am giving a few trial runs yesterday. I am not sure if their colour calibration matches mine at home.

But i am still unclear about which dpi to use. Comments please?

[cats_five]

Do you have a photo printer of your own? If you do, doing your own prints is by far best IMHO for competitions. You can make a print, have a very good look at it and do another if it's not to your likeing. If you do this via a photolab it can be a tedious and expensive business.

Remember there is no compulsion to print a 'standard' size print. Mine are all sorts of shapes, I crop the image to suit the image then worry about the paper afterwards.

Also I suspect that if you read the rules carefully, there is a maximum and possibly a minimum mount board size. Here in the UK 50x40 is the maximum as the clubs all have a display stand made to a standard and that's the biggest mount it can cope with.

My advice - print it yourself if at all possible. A4 or slightly smaller (obviously there will be some borders to trim, a rotary trimmer is the thing) is fine on a 50x40 board so long as it's a good image. 'as big as possible' isn't always best for a competition print - it will emphasise any flaws such as softness in the wrong places, distractions and so on.

I'm curious though - what sort of competition is this? Presumably not a photo club as they would give you all the information you are asking us for. Is it a competition where you all gather and the judge gives each image it's 15 seconds of fame as he / she gives the marks? How long before you have to hand-in?

[raider]

Thanks for the comments again.

No. I do not have a photo printer at home so i am not able to test out the images but i did send 2 images to the photo lab yesterday just to have a feel what kind of dpi i should be looking at. i got the photos back this afternoon.

The first image is a direct output from K-7 and so i selected 15x10 as this gives exactly 300dpi. i resized the photo to 4500 x 3000. The output is quite good and the details are nice.

The 2nd image is a direct output from my older k100D and i choose a print size of 12 x 8 so this gives me a little less than 250dpi. i would have expected that many artifacts will be seen but to my surprise, this is actually still quite good. so i think i have a certain confidence now in printing 250dpi.

I am going to try to push the k-7's output to print 18 x 12 250dpi just to see if i am right. i hope so.

I have also bought the matte board 50x40cm. i reckon 18 x 12 size is the biggest i will print to fit that board as like u say, bigger is not always better.

The competition i am trying to get into is a local council annual photo competition. while i do not think i will win, i will be happy if my photos are displayed in the public gallery as this will give me a bit of confidence boost i guess. I still have much to learn.

[artobest]

Image resolution is best expressed in pixels per inch (ppi). Dpi relates to the printing resolution, ie the output capability of your printer.

Most printers can do a pretty good job with image resolutions from about 240ppi or even less - the optimum resolution depending largely on print size and the intended viewing distance. For example, larger prints can be obtained from modest-sized files because the prints will usually be viewed at a greater distance than, say, portfolio prints.

In general, 240ppi should suffice for perfectly decent prints. You may be able to mitigate any visible dottiness by choosing matte paper, which has great dot gain (ie ink bleeding) than glossy.

[cats_five]

What is the advice from the photo lab about ppi? Also IMHO 15x10 is more than large enough for the 20x16 (50x40cm) board - I wouldn't go any larger.

[raider]

@artobest
Yes. The 2 prints that the photolab recommends me to do 2 days ago are both matte prints. I think their intention is exactly the same as yours. I am happy with the output quality. Good choice.

@cats_five
I did ask the photolab what size should i do. But I didn't get conclusive answers.

I send another 6 prints to the photolabs yesterday and i will get them back this morning. I will report back how the others go.

[cats_five]

If you intend keeping doing print competitions, getting your own printer is highly recomended! It doesn't have to be expensive - the prints from my Canon all-in-one are pretty acceptable.

[raider]

okay. i just came back from collecting my prints and as i am experimenting with printing sizes, this is what i did yesterday.

I use a couple of photos from the older k100D. These are 3008 x 2008 pixels. After doing all the photo processing using silkypix, i exported the file to tiff. then load up photozoom to enlarge the image to 4500 x 3000. in the photo shop, i print these photos to 15 x 10.

I am expecting to see a lot of artifacts on the prints this morning but to my surprise, the image look just fine. I can't tell (maybe an expert can) if that image has been enlarged in the PC or not.

So my conclusion so far (not a professional one by any means) is that a good print can result from 250 dpi onwards and it is okay for a 6 MP shot to print 15 x 10 by enhancing using software first.