JPEG / dpi resolution

[Anon]

Hey Guys,
I'm a PHP programmer and i'm working on a project which will involve alot of image resizing and sampling. Thankfully, with PHP4/gd2 i can use imagecopyresampled() and imagejpeg().

My only problem is the fact that it seems that imageJPEG() exports it in 300dpi rather then just 72dpi (since we cant see more details on monitor screens). I've been doing tests, and bring down the resolution of images (to 72 dpi in photo editor) which are created using PHP, decreases the size of the image dramatically while keeping the quality (on the computer screen) EXCATLY the same.

Is there a way to do that using PHP/GD ?

HELP!

Bedig

[[deleted]]

Does JPG even HAVE a DPI setting?

[Anon]

Vincent! I'm not sure...
You see, when i open the picture in MS photo editor and go to properties, there it gives the dpi, and you can change it. Its the same in Photoshop i believe.

I'm suprised there aren't any messages posted about this on the web. I guess its more for designers then programmers.

[[deleted]]

Editors do let you set the DPI while editing the image because they don't know what you are going to do next (save it as PSD, print it, resample it), but as far as I know, the JPG file format does not include a DPI setting, it's just a cleverly compressed bitmap that the browser puts out at the default 72dpi.

[Anon]

JPEG does appear to have a dpi setting. It's called xdensity and ydensity.

I found information about it here:
http://www.w3.org/Graphics/JPEG/jfif.txt