Re-sizing images for the web

I would avoid saving the LightRoom files as Jpegs and opening them in photoshop for editing. Jpeg is a finished format and shouldn't be used for editing.

Lightroom also has an 'Edit in Photoshop' option which works similar to the back and forth editing in Illustrator and photoshop. It'll place the file in photoshop with all the tweaks you made in light room without saving and editing a JPEG. Whenever you finish in photoshop just save it as a PSD or Tiff and it'll go back in Light Room with all your Photoshop edits and layers, then you can finish up in lightroom and change it to whatever format you want. (or if you were finished in photoshop you could just save it as a JPEG instead of a Tiff or PSD)

Just some suggestions.
 
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PPI refers to the number of pixels viewable on a screen. There is no correlation between the resolution of digital data (ppi) and the resolution of a printed image (dpi). A dot is a droplet of ink on paper and a pixel is a ray of light on your monitor.


Jon
This is not correct. Actually, it is an over simplification.

There is pre-press and there is continuous tone.

Dpi is used for pre-press printing, which is not photographic image quality.

Ppi is use for web and continuous tone printing of photographic images.
 
Thanks, Peano.

Your explanation makes sense, except for one thing:

If the middle, 'Document Size' box refers only to printing and not the screen image, why does it indicate 'Resolution: 72 pixels/inch (when pixels are relevant only to screen resolution)?

You're confusing two kinds of pixels: image pixels and screen pixels. The screen resolution of your monitor is a function of screen pixels -- the little dots of light on the panel that make up what you see on your screen.

Image pixels are the little bits of data that make up the digital image. No matter how you change screen resolution (screen pixels), you aren't changing image pixels. The best thing you can do at this point is to stop thinking that "ppi" has anything to do with the quality of the image on your monitor.

Maybe this will help make it clearer ...

pixels.jpg


Is it just a poor choice of words from Adobe?

No, Adobe has it exactly right. The "document" referred to here is the print. The dimensions are the dimensions of the print (for example 4 inches x 6 inches). The resolution is the ratio of image pixels per printed inch.
 
And regardless, 72 PPI is still the standard for screen viewing. The reason being, not that it decreases file size, but that it more closely correlates to the actual dimensions that it will be presented on-screen with at that resolution. An image resized to 600x600 pixels is going to be the same size, yes, but if you say that the resolution is 72 PPI, it'll be displayed differently than if you said it should have a resolution of 300 PPI. Similarly it changes the defaults for printing when you import the image into, say, a word processor. At 72 PPI, the image is going to take on a large document size (our 600x600 would take-up 8.33x8.33 inches) initially until it's resized down. At 300 PPI, it'll be rendered much smaller on the page and be useful for printing (2x2 inches).

Edit: Um, yeah. Basically what Peano said.
 
And regardless, 72 PPI is still the standard for screen viewing. The reason being, not that it decreases file size, but that it more closely correlates to the actual dimensions that it will be presented on-screen with at that resolution.

No, you're confusing image pixels with screen pixels.

Edit: Um, yeah. Basically what Peano said.

Right. ;)
 
hi Jon
This whole ppi thing is really confusing.
Like Peano, I pretty well ignore what it says in that box.

But..... I think what it means is that Size, Height and Width would be the physical size of the image ON YOUR SCREEN - assuming the resolution of your screen works out to be 72 pixels / in. I think the 72 ppi is an old standard though as most screens have more pixels now. Generally I think the 72 ppi figure may be useful for web-page layout.

I got used to just setting my "pixel dimensions" with the constraint on. For web-posting in galleries, I use 1800 pix on the long side and 700 on the long side for Emails - maybe 300 on the long side for sticking in a forum post (that would give me roughly 4" on the screen, right?)

Careful! .....If you change only the figure in the Resolution box you will resize the image to fit the figures in the dimensions boxes which stay fixed. So changing from 300ppi to 72ppi would greatly shrink your image size. Its a similar situation when you change a Height or Width figure.

Try changing the ppi figure to what you want then, before hitting OK, re-enter the original pixel deminsions into the upper box, hit OK and then the correct physical size shows up in the middle box without shrinking your image. For example, opening a 1800 X 1200 pixel image with the Resolution set for 300 will give me 6" X 4" (a good print size). When I change the Resolution to 72ppi, the image size indicated is 432 X 288 pix. Without hitting OK, if I change the top image size boxes back to 1800 W and 1200 H, then the dimention figures change to 25" X 16.7" - thats a big photo on your screen.

For printing, you want to watch this box that is at least 200ppi or more for the physical size you want.

- sorry for the long wind.

Hope that helps, .............. Dave
 
I think what it means is that Size, Height and Width would be the physical size of the image ON YOUR SCREEN - assuming the resolution of your screen works out to be 72 pixels / in.

No, one more time: The resolution setting (ppi) in the Image Size dialog box doesn't affect the size of the image on your screen. Look at the two images I posted earlier. 72 ppi and 300 ppi display at exactly the same size.

Careful! .....If you change only the figure in the Resolution box you will resize the image to fit the figures in the dimensions boxes which stay fixed. So changing from 300ppi to 72ppi would greatly shrink your image size.

That happens if you change the resolution and also resample the image. But when sizing for the web, there is no reason to change the resolution. Simply leave "Resample" ticked, change the pixel dimensions in the top box to the size you want for the web, and hit Enter. Pretend that the "Document Size" adjustments don't even exist.
 

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