how to get the size of an image without downloading it?

Dpi, Pixels and Print size solved!?

• I finally have a basic understanding of this subject. I called a photographic printer, and he told me my analogy for Pixel/dpi was correct. In fact, he said he would use this analogy in the future for people (like me) who have been so confused about digital photography. Below is my anology.... First....Pixels and dpi are the SAME THING! Pixels and dpi are the number of "dots" or "squares" there are in an image per square inch. Imagine you have a balloon. You blow it up to the size of a soccer ball. With a felt tip pen, you put many dots all over the balloon -so there are 200 dots per square inch ( 200 dpi). You have a choice, you can either blow the balloon up bigger or let air out and make it smaller. If you let air out of the balloon, the dots (pixels/dpi) get closer and closer together - depending how much air you let out of the balloon. If you blow the balloon up larger, the dots (pixels/dpi) will get farther and farther apart (or stretch) depending on how much air you blow into the balloon. This same analogy follows with photographic prints made from a digital camera. If your camera and disk size are such that they make an image that has a large amount of pixels/dots per square inch (dpi) you can easily make a photo of most any size that has good quality. Usually, you don't want to go below 200 dpi. You can, but it is a good reference point to shoot for to get a quality photographic image when printed. There is a formula to use to see if you have enough pixels/dpi to make a certain size print. If you know the pixel/dpi dimensions of the digital image on your memory card (or on the memory of your camera) you can divide EACH dimension by 200 (the least dpi you want in the final product). My camera (on HIGH resolution) takes photographs that have the dimensions of either 3648 pixels x 2736 pixels (horizontal image) or 2736 pixels x 3649 pixels (vertical image). To see what size photograph I can get printed at 200dpi, I do two things. If I want to know what size finished photograph I can get at good quality (200 dpi), I divided the larger number, which is 3648 dpi by 200dpi. 3648 divided by 200 = 18.25 inches I do the same for the lower number: 2736 divided by 200 = 13.68 inches Now I know that the largest print I can get with 200 dpi with good quality will be a print that measures 18.25" x 13.68 ". Anything this size or smaller will give me a good quality print. If I go larger than this size, I will take the chance of losing quality. So, for me to go to the printer, and say... "Give me a 16" x 14" print with 200 dpi isn't possible!!! The larger the print is, there won't (and can't) be 200 dpi!! He can't MAKE IT have 200 dpi! All I can ask, is for them to please make the print 18.25" x 13.68" and I know it will have 200 dpi, because I figured it out with the above formula. Any print I get that is smaller than this, will also have good quality - and the smaller I go, the more dpi there will be. Hope this helped some like me who have been sooo lost in understanding the BASICS of digital photography! I know there are probably exceptions to the above analogy, but this helped me to at least begin to understand the basics. Good luck!

• Answer:

  Unfortunately, while your GENERAL understanding is okay, your terminology is all messed up. DPI = dots per inch Pixels are just that, pixels. Pixels (or dots) multiplied by DPI (dots per inch) = length (in inches) P x DPI = LENGTH 1200 pixels x 300 pixels / inch = 4 inches 1200 pixels x 72 pixels / inch = 16.67 inches Your general understanding is fine... Your picture must have enough resolution that if output on a specific device (that has its own DPI), there's a size at which you have to scale up the picture, which would make the image blurry. You CAN make a 1024x768 (0.8 megapixels) print on 16" by 12", but the picture at that physical size is a mere 72 dpi, but the output device is VASTLY superior to that (300, 600, even 1200 dpi), so the output will look VERY blurry. Whereas if you print the same picture on a 6" x 4", the DPI you calculate backwards, is 1024 / 6 = 170 DPI, which isn't THAT far from 300, so that output will not be so bad, but it'd be ideal if the picture is printed even SMALLER, so the calculated DPI matches the output device's DPI. THEN the output would be ideal, no scaling needed.