Re: JPG compression question

Lombardi wrote:
Canon 350D
PSP X 02
RSP 2006

New to digital so will need a little help along if help posting are not off topic in this NG.
My camera is set to L+Raw but have decided to cancel the L & just shoot in raw then convert to tiff or jpeg.I need to know what the best compression rate is for jpg's.I will be Emailing most of them but need good quality to be sent.I open psp > choose my raw file> save copy as> save as (jpg)> options> save options window (need best settings here).If choose jpg opttimizer (I need best settings here)
Hope this is to long & rambling.
Thanks for help


There are actually a couple of thing you need to consider here. At the end of the day, to email a photo, you want to have a reasonably sized file, say about 50-150 kbytes as a crude target. But you need to consider what type of connection the receiving party has. If dial-up, shoot for really small files, while if DSL or Cable, they can be bigger, like maybe 300-500 kb. But how many are you going to attach? My email service starts choking at around 2 mb of total attachments.

Next, what is the purpose of the files, from the receiving party's perspective? If they are to be viewed on-screen, you should resize them to smaller pixel dimensions. I don't know the (pixel) size of files from your camera, but would guess them to be about 2000 x 3000 pixels, giving about 6 megapixels. Many people would consider 1024 x 768 to be an average size screen, with some running at 800 x 600. Depending on whether your shots are landscape or portrait, you should resize them (use the highest quality algorithm your program offers) so they fit on the screen.

If they are to be printed, at what size? Ideally, you would want around 300 pixels per inch (ppi) for the highest quality print, so a 4 x 6 print would need 1200 x 1800 pixels, but 250 ppi will usually give a decent print, and even 150 - 200 ppi is OK for snapshot quality.

As far as jpg quality, it's a balancing act. Use the highest quality you can to get the file size you need to get to, after you've resized the pixel dimensions, per your intended use. How's that for vague? Sorry, but there's not just one right answer. However, be aware that in any case, you cannot significantly reduce a file size by only cutting jpg quality without resizing it smaller first. If you do, you will see noticeable damage:loss of quality and gross artifacts - sometimes banding in the sky, or other areas with little detail.

One final thought: If your files have an embedded profile of Adobe RGB 1998 (this would result from a setting in your camera), convert them to sRGB before sending them out for general use and viewing. If you don't, they will look dull and lifeless when viewed in any application (most of them) that doesn't support color management.

So essentially, your steps are:

1: Convert to sRGB, if necessary.

2: Resize to pixel dimensions depending on intended use.

3: Save at highest jpg quality possible to get the size file you can reasonably send. If the file will not be resaved multiple times, even a quality of about 40-50% of max (don't know what type of scale your progam uses) - can be reasonable.

As a final thought, since you're new to digital, get into the mindset of thinking in pixel dimensions. Inches are meaningless for the most part, until you go to print. At that point, use the 300 ppi (or 250, or ...) x paper dimensions, but for everything else, just think in total pixels. Every program I've ever seen gets all hung up in meaningless dimension hell. Is a screen 72ppi? 96? My 4x6 file looks too big, or too small: is it at 72ppi, 120, 300, 89,352.43??? Who cares, and so what. Just think in total pixels and don't get lost in the other stuff. It just doesn't matter. Hope this helps.

Good luck.
Mike
.

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