going form 300dpi to only 72 dpi is less info, so of course it will be smaller. You are not spreading it out, you are reducing it.
Dpi and lpi are two very diferent things, research this.
If something is 300 dots per inch and you spread it out to only 72 dots per inch, shouldn’t that make the image larger?
why is 300dpi smaller than 72dpi?
you need to be looking at pixels and image size
shouldn’t that make the image larger?
The physical dimensions of the image (inches or centimeters) will increase if you have the resampling option unchecked in the image size dialog box.
This does not increase the size of the file.
If resampling is turned on, you have just reduced the numbers of pixels in the image and so the resulting file size will also be smaller.
Example:
Take an image which is (say) 3000 x 3000 pixels and the resolution is 300 ppi (PIXELS per square inch). Go Image>Size and you will see that the size is given as 10" x 10".
Now UNcheck "Resample Image" and change the resolution to 72 ppi. You will note that the size has changed to 41.667 x 41.667 inches.
The pixel dimensions, however, are still 3000×3000. – you have not changed the file in any way!
Hold Alt and click the RESET button to put things back as they were. Now CHECK the "Resample Image" box and change the resolution to 72 ppi. See, the image is still 10×10 inches – but at screen resolution. and the pixel size is now 720×720 pixels. So now you have interpolated (messed with the pixels) to reduce the size of the file.
You could, just as easily changed the image size at the same time to (say) 5×5 inches, in which case the pixel size would have been 360×360.
The important setting is the PIXEL SIZE.
Hope this helps you to understand what goes on when you change these settings.
Chris.
Sorry Cybe. Not trying to outdo you, just that you posted whilst I was still typing! Having re-read them however, the posts compliment each other admirably! <g>
Thanks for your help everyone 🙂
I was going to change the image to 72dpi, then resize for an 800×600 screen but the picture became too small. I see now that I was going wrong by leaving the resampling option switched on. Next time I’ll get it right. Thanks again for your prompt and useful replies
Fred5
Might also want to just use the Save For Web option, which does a pretty good job.
Art
You don’t need to change to 72 DPI/PPI/LPI/FBI/CIA for the web anyway. It’s true: pixels are all that matter. Save yourself the step.
You don’t need to change to 72
You do if you want to keep your file sizes down!
Um, no. That would be Pixels per linear inch
Um – thanks John. Dunno where that "square" came from. mental abberation I guess! <g>
You don’t need to change to 72 You do if you want to keep your file sizes down!
Actually you don’t. Nona is right on the button. A 320pixel x 320pixel 72ppi jpeg is exactly the same file size as a 320pixel x 320pixel 300ppi jpeg – and it won’t make the slightest different to the way it appears on a web page.
Chris.
and it won’t make the slightest different to the way it appears on a web page.
Actually had forgotten that! :-)Can you tell I work mostly in print? I was thinking of physical dimensions, and forgetting that browsers are going to display it at 72 ppi anyway.
Actually there is no such thing as 72ppi.
A web browser just displays pixels and has no clue about ppi.
So basically it is not correct to state that a browser "always displays at 72ppi". Since monitors have different sizes, the number wouldn’t have a meaning anyway.
I just wanted to add this after reading an interesting bit of info about the 72ppi myth. This page explains it quite well: <
http://www.scantips.com/no72dpi.html>
Should be mandatory reading to move that misconception out of this world. My 0.02
Most browsers recognize ppi when it comes to printing. If you tweak the CSS or HTML, you can physically scale a large JPG or GIF to a smaller height and width with greater resolution for print purposes. Of course screen display will not improve and may be worse as the browser recklessly tries to smash the image to a smaller size on the screen display.
Actually there is no such thing as 72ppi.
Thanks for that article, Faiser, but I can think of a very good reason for not putting Hi-Res images up on the web: Theives can download them and use them for print! Or am I wrong that?
I have come across Hi-Res images on the web, and have done just that (made prints, for comping only.)
John,
You’re right but nobody suggests you should put a hires online. Web images are to be resized, yes, but to a lower number of pixels, not to a lower ppi.
So when resizing, just lower the pixel dimensions and disregard the ppi.
eg. original is 3000 x 2000, for the web you want to resize to a mere 600 x 400 or so.
