Creating JPEG's Making an image as small as poss

  darkjedimistress 09:41 09 May 2003

Hi there. I want to scan a couple of photos and turn them into JPEG's, I want the photos to be of a reasonable quality but I am limited to only 50kb per picture so I am wondering what the tips are when scanning etc so get a picture file size down while trying to maintain a decent quality of image. I presume changing the number of colours would be a good starting point but does anyone have any GREAT tips for helping out with this?

  Gongoozler 10:06 09 May 2003

Hi darkjedimistress. The first consideration when scanning the pictures is what you want the pictures to be used for. The number of colours doesn't have much effect on the file size, but the number of pixels does. If you have graphics processing that gives you control of the jpeg compression factor, this will enable you to get smaller files even with a relatively large number of pixels, but even basic software such as Irfanview enables you to resample to a smaller number of pixels. If the scanned photo is to be viewed on a computer monitor, match the resolution to the monitor, i.e. if the monitor resolution is 1024 x 768 pixels, then there is no point in going higher than this, and 1024 pixels from a 6 inch photo is only 170pixels per inch. If the photo is to be printed at 6 inches x 4 inches, then the same resolution will also be enough, and equates to nearly 1Mp from a digital camera.

  DieSse 13:45 09 May 2003

The are two aspects to "size" for pictures. One is the size of the picture in terms of the number of pixels it contains, and the number of colours. How you affect this, as is described above, depends on what you want to do with the picture. For displaying on a screen only, a pixel density of above 100 dots per inch is virtually wasted. A 17" screen at 1024x768 has approximately this dot density - thus a picture scanned at 100 dpi would appear on the screen at around it's actual size. For prinitng, around 300 dpi for scanning is likely to produce a better finished result.

A 6x4 picture scanned at 100 dpi will contain 240K pixels if scanned in black and white - in 16 bit colour, 3.84Mb. An A4 picture scanned in 16-bit colour at 300dpi will produce a file of over 100Mb (all figures approximate).

That produces the starting point. To get the file size down - you need to compress the picture - the standard compression is jpeg - this is used all over the web and for email, and in most digital cameras. Now the amount of compression when coverting a file to jpeg is variable - you can set it yourself in the program. The more compression, the smaller the file (NOT the image) and the poorer the quality. The fairly standard settings chosen in most programs, unless you change it, reduces a file to around 10 to 20% of it's original size, with no big loss of quality. for a 6x4 picture sacnned at 100dpi this would reduce to about the size you want.

Most photo handling programs have options to convert, or save, in jpeg format - and you can get at the options to try different compression ratios. You can experiment to see the resulting quality and file size very easily.

But - to re-iterate, it all depends on the size of your oringinal, and what the end use of the picture is to be.

  DieSse 13:58 09 May 2003

I should have added, how you go about all this also depends on what version of Windows you have, what scanning software you use, and what phot-manipulation software you hae. Scanning and sending to eamil is particularly easy in Win XP, for instance.

  Pesala 14:02 09 May 2003

Photos usually compress well with little loss of quality. See this earlier thread for some sample images at different compression ratios: click here

  brittas 14:30 09 May 2003

I happened to have the same probs the other day so experimented with hp scanning software and photoshop. Scanned at best quality in hp and saved as jpeg THEN opened in photoshop and saved in jpeg but in medium size (no 4 on the scale that it shows you) which halves the size but keeps the quality. I tested by opening before and after in acdsee 32 viewer ( you can use what windows defaults to ) and both looked the same but with the finished article being half size !!!
sorry it sounds long winded !!!

  darkjedimistress 14:48 09 May 2003

Windows ME, using a standard flatbed UMAX scanner that allows me to choose DPI to whatever I wish it and am formatting images using Paintshop Pro 7. I am only wanting to view the images on the screen and they are not for printing, I just want to create an image on screen about 3 inches by 4 inches at most and for it to be as clear as possible. Thanks for the help so far, I'll have to try a few of the tips at home this evening.

  Gongoozler 15:28 09 May 2003

Hi darkjedimistress. 4 inches on a 17 inch monitor screen with 1024 pixels is only about 300 pixels. If you are scanning a 6 inch wide photo, you will only need 50dpi. This should give a very small file size when saved as jpeg. If you have the option to select the compression factor you can experiment to see how far you can go before you can see the degradation.

  woodchip 15:54 09 May 2003

If you are wanting to send these images over the net 50KB will be OK. But you are not going to get anything like quality at that size unless the picture is very small even in jpeg, This also depends on the subject matter ie is there a lot of detail in the image. My own from Digital camera are from about 80kb to 125kb A4 at medium resolution

  darkjedimistress 09:26 12 May 2003

Excellent as always. Thanks everyone, I got the image I wanted, quality was great. Hope this query helped others to!

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