Photo Compression

KR
Posted By
Kelly_R
Nov 2, 2005
Views
361
Replies
8
Status
Closed
I work for a screen printer and I noticed some photos that people send us Look great no matter what size i make them and they are small file sizes. how can you scan a picture and have it look great/ high quality at any size and still keep a relativly low file size??
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DM
Don_McCahill
Nov 2, 2005
What kind of files are they?

I think the smallest compression you can get is from the jpeg format. This is a lossy format, however, so it should only be used once (don’t save a jpg as a jpg over and over, or it deteriorates). A good non-lossy compression is TIFF, but the files are much bigger than jpg. If a file is composed with mainly solid colors, GIF will probably be smaller than jpg.

Don
D
deebs
Nov 2, 2005
Kelly R: that, in a nutshell, is the 64,000 USD question.

It’s the Holy Grail of image processing how to create a small filesize and maximise image quality at the same time?

At one end of the scale is BMP at the other….

Well, there are lots of options.

Limited color range = try GIF
For swift downloads = try JPEG
(BTW JPEG has been around for years and people such as digital camera brand holder have latched on to it that should say something about how good the JPEG spec is. Not many file format/specs last quite so long with so few revisions)

If it can be vectorized = use a vector format but the trade off is lower filesize = potential for greater delay as the vector information is decoded, rendered, displayed.

Is there an easy solution?
(Ans: probably not)
KR
Kelly_R
Nov 2, 2005
thank you for your reply!

I was sent an illustrator file with a black and white photo alread in it. It was rather small it was about a door hanger size piece of material. and i was able to size it to a 4ft x 8ft sign which the photo turned out to be about 2ft wide at least.

So what does resolution have to do with the quality and file types…. the file for print must me 300 DPI
so is this to say that file type is more important then the DPI? this photo is really making me think…
D
deebs
Nov 2, 2005
Thinking is (IMHO) good for you 🙂
DM
Don_McCahill
Nov 2, 2005
Illustrator is a vector format. Vectors can be scaled indefinitely. As for the photo in it, black and white will scale better than color, and it may have been that this particular image scaled nicer than others would.

The DPI (more properly PPI except in actual printing) is very important. If you start with a 300 ppi image, you can enlarge it three or four times and it will appear sharp online, since that only represents about 72-100 ppi.

It is not true that for print an image must be 300 ppi. It depends on the line screen that it will be printed at, and usually the ppi needs only be 1.5 times the line screen. Thus most printing will work well at 200 ppi.

Don
BO
Burton_Ogden
Nov 3, 2005
JPEG 2000 is much better than JPEG at high compression ratios. For a dramatic comparison, see the LuraTech website <http://www.luratech.com/>.
KR
Kelly_R
Nov 3, 2005
ok this might sound dumb but what is PPI?
DR
Donald_Reese
Nov 3, 2005
Pixels per inch

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