What is the pixel count you want for online images? 

Understand that unless you're trying to give people images they can print as big enlargements, you probably don't need more than 1 to 2 megapixels in a "high resolution" image for viewing online.  Storing web images in too large a size just means they'll take more resources to download and people won't want to look at them as much.

Is this enough?  Too much?  It's 1400 x 1052 pixels (1.5 megapixels), about 800 kbytes.

http://Noel.ProDigitalSoftware.com/ForumPosts/DecentPixelCountForScree nViewing.jpg

-Noel

The file size is affected by the compression algorithm employed in creating the file. There is a trade-off of image quality for size reduction. However, there is often no significant perceived difference between uncompressed or lossless compressed images and "high quality" or "very high quality" lossy compressed images, while there can be significant or huge file size differences.

It's really as simple as this:

Pick a target set of pixel dimensions you'd like to publish your images in.

Process your files through Camera Raw and Photoshop, and downsample for publishing to the size you've chosen.

Choose a JPEG compression amount when you save your images for publication that looks good enough to you on screen, and provides a reasonable amount of compression so as not to make people wait too long for the download.  I suggest starting with quality level 9 or 10 (I believe I used 10 on the image I provided a link for above).

-Noe

Downsampling is what you do when you reduce the pixel dimensions in the Image - Image Size dialog with the [  ] Resample checkbox checked.  I'm talking about processing the images at the resolution out of the camera (or even higher) for best appearance, then doing Image Size right at the end when you're ready to publish them.

Yours are what I would call low to medium resolution.  585 x 400 pixels wouldn't give you a sharp full screen display even on a small monitor or tablet.

If you have full control over the HTML in your own web page, some time back I prepared a web page that uses HTML to downsample images for normal display at 100%, so that they stand up to being zoomed-into - e.g., on an iPad, or by using the zoom function in a browser.  Where's that URL...   Ah, here:

http://Noel.ProDigitalSoftware.com/temp/WebImage/Test.html

That's just a graphic, but the larger of the two, which will stand up to being zoomed in to 200% (and display really nicely on a Retina display) is 1000 x 1188 pixels.  The <IMG> tag initially displays it at 50% of its true size.  With this technique the user downloads a bit more data but the image stands up to close scrutiny much better.

-Noel

cma cma wrote:

 

... if I were using jpgs of say 877 X 600 px, they would be larger on the screen than my current jpgs,  but would the larger jpgs be higher resolution?

 

The resolution (pixels per inch) would be that of your monitor's screen and therefore the same for all displayed images.

It seems to me that they would have to cover more screen space, so doing Image Size at 877 X 600 would result in the same apparent visual resolution (fineness of detail) as my current 585 X 400 px images. What am I missing?

More pixels will contain finer detail, of course (unless you create the large image by upsampling the small image).

Just to add:  One thing you can usually do is with the larger pixel count images save them at a higher level of compression (lower Quality setting) and the sizes won't be 4x the size of the smaller JPEGs.

I have just updated the web page example I provided above to include an image as well as the graphic.  The much more detailed image is only about double the size as a JPEG file as the smaller one.  The Quality setting was 7 vs. 10.

-Noel

Not as much as you'd think.  See it for yourself on my example page.

-Noel