Do image dimensions effect picture quality?

[Liamsford]

My Canon Rebel XS shoots photos at the dimensions of 3888 x 2592 (when horizontal) and it seems like because of that, the photos are also a really big file size. I've only uploaded 29 pictures to Flickr, and my month's limit was already reached.

Does the dimensions of my pictures effect the quality they are? Seems like my friend who also shoots, his pictures are 1/3 my size and his pictures are a lot sharper.

Thank you! & if the answer to the title is yes, is there a way to change this to make my pictures not so big? & what size is suggested?

 

[Garbz]

Only when you view them full size. No one will do that on flickr typically. I resize them to about 1024 pixels wide. KEEP THE ORIGINALS, DON'T SAVE OVER THEM.

 

[Big Mike]

Remember that the basic purpose of a camera, is to create photos, which for a very long time, meant that you wanted to end up with a print. To create a print from a digital photo, you need pixels and plenty of them.

The usual rule of thumb, is that you want 300 pixels per linear inch of print. So you your file size, that's just over 12" x 8". That's a good sized photo, but it's not huge. You can easily make bigger prints, but the quality of the print goes down as the print gets bigger.

So that's why your camera gives you all those pixels....but you don't need them for viewing on a computer screen. Screen resolution is usually around 72 PPI, so you file on a screen (at 100% magnification) would be 54" wide. Obviously, you view the image at a lower magnification to see the whole thing on your screen.

So if you figure out how big you want your image to be on the screen, you can figure out how many pixels it needs to be. For example, something like 800 pixels wide by 600 pixels high would be a nice size. It would also make a much smaller file size.

So to finally get to the point...you can reduce the file size in two primary ways. The first is to resize the image to fewer pixels (set the PPI to 72), and the next is to set the compression/quality level. When you save (save-as) a JPEG image, you can set the compression level. You can probably set it as low as 50% without noticing much or any degradation in the image.
So by resizing the image, and setting the compression level, you can greatly reduce the file size.

Photoshop has a 'save for web' tool that does all this in one step.

I'm sure that most other image software has the option to do this as well.

And yes, ALWAYS SAVE A COPY, so that you don't overwrite your original large file.

 

[JG_Coleman]

Does the dimensions of my pictures effect the quality they are? Seems like my friend who also shoots, his pictures are 1/3 my size and his pictures are a lot sharper.

Thank you! & if the answer to the title is yes, is there a way to change this to make my pictures not so big? & what size is suggested?

A couple things...

First off, an image of reduced size almost always looks sharper than the larger source image from which it was created. Slight flaws in focus, motion blur, and camera shake become less and less apparent as you reduce the size of the photograph. So, for example, some photographs seen on Flickr at such a small size may not be as technically excellent as they seem. Reducing a digital image to 1/3 of it's original size will very often have the effect of making it appear sharper... simply because it's so heavily reduced in size that flaws in the level of sharpness can no longer be easily discerned. It's more of an optical illusion, really.

An image that looks super-sharp in Flickr may not always make the nicest 12" print (when printed using the original source file). When a large print of an image is made, problems in overall sharpness become more and more apparent... and sometimes images that look superb on Flickr at reduced sizes make downright terrible prints when the each individual pixel of the source image is called upon to produce a full 240 - 300 ppi for a large print.

That being said, I resize my photos to be just large enough to fill the available display space on most of Flickr's pages. So each photo I upload has been reduced to roughly 600 x 400 pixels (the same aspect ratio as my camera's originals). There's really no need to make them any larger than that unless you specifically want people to be able to see a larger version. Resizing them in this way will save you a TON of space.