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Resizing Images

Do some file formats (gif,jpg,bmp,etc.) lend themselves better to resizing then others?  I seem to have alot of problems trying to make images smaller without losing clarity.  I have been using the resize/resample function in irfan view to attempt to do this.  Mostly they are screen shots that I am trying to make smaller so they can appear in user manuals.  I have used GIF and JPEG and there doesn't seem to be much difference in those.  Any ideas.tips appreciated!
1 Solution
Hi, snyperj,

When working with a typical screen capture (of around 72 DPI), I don't think you will have much different success with one format over another.  BMP is the best to START with as it is the original image representation without any prior loss of quality due to image compression (as in JPG or GIF).  Since JPG and GIF have already been compressed once (with who-knows-what-kind-of-quality-loss), compressing again further deteriorates the quality.  And so-on and so-on each time you edit it and save it again.  

Not sure how much your are resizing but a small amount should be too bad...say, 10% reduction.  If you start moving down to 50% and higher, I think it's hard for any program to do a successful interpolation.  Let me give a drastic example.  Let's say you have a sword (held at a diagnal) in an image and to show that sword, the image uses 200 pixels along one edge.  BUT, now we shrink that image by a BUNCH.  So much so that now the image only has 10 pixels to show the edge of a sword that used to be delineated with 200 pixels.  I'm thinking that sword edge is going to be REAL jaggedy.

That's a drastic example but done to show what I mean.  Everytime you shrink an image, pixels are discarded and the algorithm does its best to condense the remaining pixels to show the image the best it can.  And not always successful.


-> small amount should be too bad

Should read:  "small amount shouldN'T be too bad"

Assuming you are using these images for print, I think resolution makes more difference than format. Before resizing, try upping the resolution to at least 300, then resizing. You may want to sharpen afterwards too. (assuming you have photoshop)

But remember, its ALWAYS better to go big to small when resizing than it is to go small to big.

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Another thing that should be mentioned is that the application you are using to resize the image DOES make a difference. Different programs have different algorithms for resizing images, and some are clearly better than others.

Adobe Photoshop is obviously one very good program when it comes to resizing images. If you compare the results from several different programs, you should be able to notice some quality differences.
Jose ParrotGraphics ExpertCommented:

I am a heavy user of IrfanView. It is a superb piece of software. The resizing algorith embedded in it is very good, even to enlarge images.

For captured screenshots, my recomendations are:
1. Capture and save as BMP in full color 24 bits per pixel. No compression and no loss. Large file.Delet it later, after reduction
2. Open ithe image with IrfanView. Improve contrast and saturation, within Enhance Colors.
3. Reduce to desired size with resampling option chosen.
4. Chose PNG format to save. Why?
   a. No resolution losses due compression algorithm, as occurs in JPG
   b. No color losses due format limitation, as occurs in GIF
   c. Widely accept, as both jpg and gif

If possible, try to reduce by modulo 2, that is, half size. The maximum efficiency on quality image is achieved in that relationship between original and final image. Lets here consider if the image is for a printed manual or for a  manual to be seen at screen. For printing, the higher the resolution, the better printed image. So, a image sey, 1200 x 1200 pixels, if printed at 1200 dpi, will be 1 inch x 1 inch of very good resoltion quality. If you will use Microsoft Word to prepare documents for printing, you can insert the full size images, and let Word to resize it. Word's algorithm to reduce images at Word document works fine. Really fine.

For screen viewing, things are simpler, because you watch the actual image as in the future document, for exemple, a home page.

So take on count of the viewing proccess and the resolution sets you are working on.

If you prepare a number of images for reductions of same ratio, you car run IrfanView for batch execution. Not bad.

So, remember: for printing don't reduce images, do use of printer resolution (600 dpi to 2400 dpi).

A hint more: if a text is 24 pixel high, if you reduce with resampling, antialiasing algorithms will de applied, but even in this case, if the reduction is in a ratio of 3.5, for instance, the readness will be affected for sure!

make sure you select the correct image quality level before saving.
there you should have a slide:  "lowest"  to "best"

go for best and check out the image quality now.


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