View Full Version : Resizing jpegs

John West
08-24-2006, 04:01 AM
Now that I'm posting a bunch of stuff here, I often have to reduce the size of my jpegs for posting elsewhere, or sending by email. Is there any loss of quality when I use Photoshop to reduce the size of a jpeg file?

John West

08-24-2006, 07:07 AM
It all depends on whether you choose to resize the picture to a smaller pixel area (by cropping), or if you choose to save it at a lower image quality (i.e., compress in the Save As menu). Resizing would be the way to go to keep the image as close to the original. As long as you keep the picture at the size you resize it to, and no higher, it will look fine. Say you have a shot at 1024x768, and you resize it to 800x600 to take up less file space. Theoretically, it should look just as good either size, same details except smaller visual translation. If you try and stretch the 800x600 out to 1024x768 though, and hold the two side by side, the pixels in the 800 one will be much larger than the 1024s original ones, and will translate to lesser image quality.

08-24-2006, 03:54 PM
John West asked:
Is there any loss of quality when I use Photoshop to reduce the size of a jpeg file?

When you resize a photo from 1024 pixels wide to say 600 wide for email purposes, Photo Shop has to interpolate a whole new set of pixels from the larger shot. There is going to be a loss of detail in this process. Also, any existing jpeg artifacts are going to be magnified.

If you were to save at the same jpeg level, there should be minimal additional increases in jpeg artifacting and color compression, but every save in jpeg does decrease quality. Also, to save bandwidth, I generally reduce the quality from 12 to about 6 when I save for email. Many email programs won't accept emails greater than 1 meg. Displayed at screen size, the losses are minimal visually, but of course, if you tried to restore the shot to 1024 you would have garbage.

If you really want the best possible quality in your downsized images, you should probably make the 600 dpi image from your original TIFF, but for email, why bother? If you want someone to really see the image at its best, send it to them at 1024, after you are sure it will go through.

Michael Allen

08-24-2006, 08:45 PM
every save in jpeg does decrease quality

Exactly right. In short if you open and save a jpeg repeatedly, you decrease quality. Opening and saving as photoshop or similar file will not, so its a good idea to save edited images as psd files as well, in case you ever want to make additional changes.