I am new to this forum and would like some advice. I understand that the pictures to be uploaded must be 800 pix at the longest side. However, there seem to be no restrictions on the oicture resolution. What is the optimal resolution of the pictures to be posted? For example, 72 dpi, 96 dpi, 250dpi or 300dpi?
It doesn't matter. (On the screen) 800px is going to be the same no matter what. It only matters when you print it. For 72 dpi, 6in would be 432px. For 300 dpi, 6in would be 1800px.
Well, there is no such thing as dpi when viewing onscreen. 800px at 72 is exactly the same as 800px at 72,000. The dpi means nothing. You can pick whatever number you like
There is actually no "optimal resolution" for uploads since they are displayed at what amounts to 100% magnification at the size you send - e.g. one pixel in the image displays as one pixel on the viewer's monitor.
This is another way of saying, "It doesn't matter." If you upload an image with 400 x 400 dimensions that has 72 dpi resolution and another version of the same file that you change to 300 dpi... they will look exactly the same on the screen. (The relationship between image size and resolution is important when you print.)
So the real question - at least in this regard - is simply what pixel dimensions to use. There are various thoughts on this, but one thing you could do is simply find an image here that seems about the size that you would like to use, download it, open it in your image editing software, and see what the dimensions are. (It would be appropriate to delete the image from your computer after you do this.)
My own "policy" about photographs that I post online is to make them rather small - the longest dimension of the photograph itself is 600 pixels. (So a typical DSLR shot that hasn't been cropped might have image dimensions of 400 x 600.) I add a border to this that includes my name and URL - not specifically for posting in this forum but as a general online posting policy. (I have reasons for this - but I'll only go off on that tangent if others are interested in hearing more.)'
I think that 800 pixels on a side is a pretty common size for posting as well - though users of common small laptops will have to scroll if you upload a vertical format image. Some post much larger and there is no question that a fine photograph displayed at larger sizes on a calibrated large monitor can be an impressive thing. However, there are reasons to consider not going so large - these include: many view on laptops and cannot see the full image without scrolling, some may have slower connections and the download times can be longer, when multiple images are included in a single post it can become huge, and you may not want large high quality versions of your images floating around in cyberspace. (Or maybe you do - and that is your choice.)
Other issues:
Color space matters - sRGB is the safest choice. (Some newer browsers are color managed and can accurately display other color spaces, but until all browser are color-managed you are taking a chance.)
8-bit jpg files are generally the best, most universal option for uploading.
The quality setting should be high enough to produce a good quality online image but probably not the very highest settings since they make very large file. I use a setting of "8" in CS4.
