Saving JPEG Files

[Jason Newton]

Hi everyone,

I know this will be a rather simple question for some people but I cannot find an answer anywhere.

If I have a jpeg with a file size of 570kb and then I perform something like change levels and then save the file, how can I make sure that the file is saved roughly at the same size as the original?

Is there any advantage to saving at a larger size?

For example, taking a file 0f 500kb and saving it as 1mb. How does this change the image?

I don't really understand about the compression. Ideally, I would like to be able to save the file at the same size as it was originally rather than compressing it.

Kind Regards

[Per Berntsen]

The jpg format uses lossy compression, which degrades the image to a certain extent.

Every time you save a jpg, the quality is reduced, and it's possible to destroy the image if you save it enough times.

In addition, jpg files are 8-bit, and editing will also reduce the quality, the histogram will quickly start to look like a comb, indicating that there are missing levels (tones if you like) in the image.

The file size of a jpg depends on two things - the amount of compression used (quality setting) and image content. Images with a lot of sharp detail generally means a larger file size, images with large flat areas generally means smaller file size.

Jpg is designed to be a final format - you can open the file and look at it, or print it.

If you have to edit a jpg, open it in Camera Raw, and do your edits there, Camera Raw does non-destructive editing.

(Right click the file in Bridge, choose Edit in Camera Raw)

After editing, click Open in Camera Raw, which will open the file in Photoshop. If you plan to do further edits in Photoshop, make sure that that you have chosen 16-bit in Workflow options (click the link at the bottom of the Camera Raw window), and save the file as a Tiff or Psd in Photoshop. 16-bit files can withstand heavy editing without losing quality.

As for file size, unless you are creating images for the web, forget about it, and concentrate on quality instead.

I've written some articles that you may find helpful -

File formats

What is a digital image?

[Jason Newton]

Thanks for your long and detailed reply. It is most helpful.

I will have a look at your articles too.

Thanks again.

Jason

[Stephen_A_Marsh]

I’d watch the following movie if you are going to use ACR to “edit” JPEG or TIFF files:

http://getmadcat.com/video/64039/Tip-64-JPEG-and-TIFF-in-Camera-RAW.html