Posts Tagged ‘Resolution’

I was pointed to a couple of blog postings yesterday, one called The Myth of DPI and the other titled Why DPI Does Not Matter.

Their arguments are logical and faultless. Their reasoning is sound. The message they are trying to get across is correct. But they are both wrong.

So why are they wrong?

Because they are writing about images on the web, and mentioning DPI. When you set the image size and resolution in Adobe Photoshop you never have the option of choosing the DPI of an image. This is what you get if you choose inches as your preferred units:

and this is what you get if you choose metric:

The option you have is of choosing “pixels/inch” or “pixels/cm”. Not “dots/inch” or “dots/cm”. Adobe Photoshop is concerned about your digital file. It doesn’t give a monkeys what you intend to do with it later. So it offers you ppi, NOT dpi, which is used in printing terminology. 300 pixels per inch equals 118.11 pixels per centimetre.

Our earnest bloggers are absolutely right in that ppi is irrelevant when you’re showing images on a screen. But dpi is relevant when you print those images, because then you can figure out how large you can print the image before those annoying little pixellations get in the way and become visible. 300 dots per inch is generally enough for the human eye to be tricked into seeing continous tone.

fotoLibra has always demanded that images uploaded to its site should be 300 ppi, for two perfectly valid reasons — and one utterly compelling one. You can read about them here.

I agree with my friends Ben Gremillion and Svein Wisnaes that resolution counts for nothing on the web. So it generally doesn’t matter, until you come to selling your photographs. When you are selling photographs to book publishers who need to print them at 300 dots per inch, it’s common courtesy to supply them at 300 pixels per inch.

Otherwise they might buy them from someone who took the trouble to go the extra step.

Gwyn Headley

by Gwyn Headley

Managing Director

300 ppi. That’s the resolution we demand for images uploaded to fotoLibra.

Lots of people say 300 dpi instead of 300 ppi. That’s dots per inch, which is what printers use, but digital images appear on digital screens, which use pixels. So we say 300 ppi.

As soon as you know a little bit about digital photograpy, you will learn that the resolution of an image makes not a blind bit of difference to the quality or size of the image. The majority of cameras deliver their digital images at 72 ppi, whether you choose the RAW or the Basic mode.

Why then is fotoLibra so cussed as to insist members go through the palaver of converting their images from the perfectly adequate 72 ppi to 300 ppi?

We do so for two perfectly valid reasons. And one utterly compelling one.

Firstly, I’ll answer the question our poor Support team has to fend off more than any other — How do I convert my images to 300 ppi?

It’s a doddle. You can probably do it with the software that comes with your camera, but as they all differ I’ll describe the process in Adobe Photoshop. Don’t have Photoshop? Try Adobe Elements. Don’t have Elements? Irfanview is free and does the same thing, and much more besides. If you have a digital camera and you intend to sell photographs through fotoLibra, then you must have image processing software. It’s your darkroom.

This is what you do in Photoshop: go to Image> Image Size> UNCHECK the Resample Image button, and change the Resolution to 300 pixels / inch. Save the image. If you go to File> Automate> Batch… you can easily apply this to all your images.

That’s it.

If you see 118.1 instead of 300, you’ve chosen pixels per centimetre instead of pixels per inch. It’s exactly the same.

We don’t often reveal the first two reasons why we impose a resolution of 300 ppi (no more, no less), because when we do we usually manage to upset both buyers and sellers. This doesn’t apply to YOU, of course. So apologies in advance.

  1. Our buyers, who in the vast majority of cases will be printing the images they buy at 300 dots per inch, do not care for the extra work involved in carrying out this operation, and they complain when they get an old 72 ppi image which they have to convert. So we like to supply them with the resolution they prefer.
  2. It makes members think before uploading the moment they snap an image, and to look carefully at their photographs to see how they can be improved, and if they are uploading truly saleable pictures.

I know you know all this, and I know your images are always 300 ppi and you’ve never had any problems uploading, but spare a thought for a few of your fellow members in difficulty. I hope this helps to explain things.

In the background I can still hear whispers. “It’s really not relevant. Why make such a song and dance about it?”

OK, here’s the cruncher.

Have you ever discovered porn on fotoLibra?


Yet it’s the world’s first Open Access image library. Anyone can upload anything.

Why is there no porn? Because 99.9% of it falls at the first barrier. What self-respecting porn merchant is going to go through the admittedly very minor hassle of converting his 72 ppi images (which are only ever viewed on a screen) into 300 ppi so he can upload them to fotoLibra? He’s going to go somewhere less stringent, less careful. Somewhere he can harvest mugs. He won’t find them on fotoLibra.

We also check every image uploaded. One or two may get past the 300 ppi barrier; they won’t get past our picture vetters.

Since the first upload to fotoLibra in March 2004, we have only had to reject four images.

We must be doing something right.

And that’s why we ask for this tiny imposition on your time.