A question about camera resolution!

[romero]

Hello! Yet another new member here. Firstly, an apology - I am not a photographer, but an artist who paints in oils and has to take photos for his website. My question is probably a simple one to answer as far as you are concerned, but having read numerous threads on the subject, I'm still baffled. I have a Sony Cyber-shot 7.2 mp digital camera (told you I wasn't a photographer!) and wish to have the highest quality images possible on my website. I have the camera set on the maximum capacity, which supposedly provides images up to A3 size, far larger than I need for the site. The maximum size I use on the site is 540 x 680 pixels and the photos are imported into my Mac at 72 ppi. I have been assuming that although the screen resolution is around 72 - 98 ppi, increasing the image resolution to 300 ppi as I reduce the pixel size will give an improved image. I use Gimp software, which has "Sinc (Lanczos3)" interpolation. I would really welcome some guidance from you experts. Many thanks.

[Colin Southern]

Hello! Yet another new member here. Firstly, an apology - I am not a photographer, but an artist who paints in oils and has to take photos for his website. My question is probably a simple one to answer as far as you are concerned, but having read numerous threads on the subject, I'm still baffled. I have a Sony Cyber-shot 7.2 mp digital camera (told you I wasn't a photographer!) and wish to have the highest quality images possible on my website. I have the camera set on the maximum capacity, which supposedly provides images up to A3 size, far larger than I need for the site. The maximum size I use on the site is 540 x 680 pixels and the photos are imported into my Mac at 72 ppi. I have been assuming that although the screen resolution is around 72 - 98 ppi, increasing the image resolution to 300 ppi as I reduce the pixel size will give an improved image. I use Gimp software, which has "Sinc (Lanczos3)" interpolation. I would really welcome some guidance from you experts. Many thanks.

Hi Romero,

PPI is really only relevant to a paper print ... on a monitor the pixels are physically set by the manufacturer at around 100 PPI for a modern LCD screen. If you chuck a "300PPI" image at a monitor, one of two things will happen (or a combination of both) ... either the image will be displayed at 100% magnification (ie one pixel in the image is represented by 1 pixel on the screen) - in which case the image will appear 3 times wider and 3 times higher than you want - or - (if the image is displaying at the right size) then the monitor will only display 1 pixel in every 9 from the original (1 in 3 times 2 dimensions) (ie 1 in 3 vertically and 1 in 3 horizontally).

If you're wanting 540 x 680 pixel images for your website then simply down-sample the full resolution images to this size ... and the quality will "be whatever it is" (don't forget some output sharpening though). The ONLY way to get higher quality images is to provide an image with more pixels in it - have it normally display at a modest size - but have it expand if clicked ... like my image below (click on it to expand it).

Hope this helps

[xpatUSA]

. . far larger than I need for the website. The maximum size I use on the site is 540 x 680 pixels and the photos are imported into my Mac at 72 ppi. I have been assuming that although the screen resolution is around 72 - 98 ppi, increasing the image resolution to 300 ppi as I reduce the pixel size will give an improved image. I use Gimp software, which has "Sinc (Lanczos3)" interpolation. I would really welcome some guidance from you experts. Many thanks.

I would recommend that you forget about ppi - which only relates to how your image file will get printed, as in - on a printer. How it appears on-screen is much more simple and you could almost forget the word "resolution" (I'm going to get jumped for saying that).

So as you are an artist, should I now be cracking pointillist jokes, ho ho?

OK - say your screen has 96 dots per inch. Another way of saying that is each dot is 0.264mm wide. My screen is about 86 dots per inch, BTW.

If you are posting 540x680px images on your website, they will show up on your screen at 5.63" x 7.08" (I divided the pixels by the dots per inch). On my screen, your image will show up at 6.28" x 7.91".

When you said that "the photos are imported [from the camera] into my Mac at 72ppi", that ain't really so - trust me. They come in at whatever JPEG size in pixels you set in your camera. Any setting that mentions "ppi" has only to do with printing. And "increasing the image resolution to 300ppi" will make your printed image smaller, and will make no difference to your website image size.

The sinc(Lanczos3) interpolation is a better quality method for re-sizing images but has nothing to do with ppi per se, other than the fact that a re-sized image will obviously be bigger or smaller on-screen.

NOW, if you take your 540x680px image and set it to 72 ppi and print it, the print will be a certain size. If you then double the image pixel size but print it at 144 ppi, it will print at exactly the same size as before. Of course, the image will now be double-size on-screen.

Hope that helps,

[romero]

Thanks for your input guys. So, if we ignore the printing issue, you both appear to be saying that whatever I do on my Mac (apart from the 'sharpening'), the image quality will not change. Even if I had a larger image link, and accepting there would be more pixels, the quality would surely remain the same. It seems the answer is a higher quality photograph to begin with, and this being so, which is the most effective way of me accomplishing this please? I always seek good daylight and keep still when taking the photographs. Do I need a better camera? Maybe one with a larger lense?

Oh, and by the way, I understood 'pixels per inch' to relate to screen resolution and 'dots per inch' to print.

[Geoff F]

Yes (I think); you now clearly understand the theoretical difference between ppi and dpi.

And increasing the size of an uploaded image, to a monitor, doesn't make any difference to how that image is displayed on the monitor (quality wise). Providing the image is at or beyond the capacity of that monitor.

So uploading a photo at 5000 pixels wide, no matter what resolution, will not show any better than a 1000 pixel image; if your monitor is limited to 1000 pixels. Actual max sizes will vary depending on the monitor used.

Which helps to explain why some of my images look better in a print than on my monitor.

However, uploading massive files to the internet will take extra time to transfer all that data, and could cause problems if you have a max file size limit.

Printing on the other hand is a different matter; where more pixels mean a larger print, providing you have sufficient pixels to comply with the printer requirements.

For instance an image for printing with a resolution of 300 ppi will print fine at the designated print size. Setting the printing resolution (for the computer) at 1000 ppi would not improve the print quality. However trying to print at a large size with too low a resolution, let's say a specified print size which gives 100 ppi or less will produce a poor result, slightly depending on the actual image and paper.

A specified print size at 200 ppi should print OK for most papers.

Printer dpi tends to work around 360 dpi for cheaper soft papers rising to 2880 dpi for the finest quality gloss prints. But this is really another subject entirely.

[Colin Southern]

Hi Geoff,

You're on the right track, but nothing is ever cut and dried I'm afraid.

In reality, DPI doesn't so much define print quality as it does minimum viewing distance. If you take a couple of real-world print examples of say 75 DPI and 300 DPI - BOTH will look sharp when viewed from 3m away.

In summary it comes down to the common question of "how big a print can I make from a ABC Camera" -- whereas the answer is "as big as you like", but at some point the degradation in quality will become visually obvious.

With regards to monitors, if you feed an image to a monitor that has a higher resolution than the screen then the image will probably be down-sampled by the browser - and down-sampling affects sharpness. In that regards you'll normally get a better result where the image is the right size to start with and is correctly sharpened for that resolution.