gif export question

[RTK]

Is there a difference in image quality between a gif exported at 75% from vectors and a gif which is rezised to 75% and re-exported?

I'm blind as a bat and can't tell. Is there a difference (even a mathematical one)?

Could someone enlighten me?

Risto

diri@videotron.ca

[RTK]

Is there a difference in image quality between a gif exported at 75% from vectors and a gif which is rezised to 75% and re-exported?

I'm blind as a bat and can't tell. Is there a difference (even a mathematical one)?

Could someone enlighten me?

Risto

diri@videotron.ca

[JF Slater]

And I also want to know how to resize a jpg and keep the same quality. If the first one was 70% quality when you you import it, would you export at 70% again or at 100%?

Obviously I'd use the original Xara files if i had 'em

Jessica

[mckinney]

Risto and Jessica - I think you are asking two different questions here. I'll make my stab at each.

Regarding the jpeg scaling:
As far as I know, it's not possible to scale a jpeg file and re-save it as a jpeg without the introduction of further image artifacts. If you have a jpeg that must be resized and file size is an issue, then I suppose I'd experiment with the compression setting on the jpeg export to get the best compromise between image quality and file size. If file size is not an issue, then I'd save the scaled bitmap as a tiff file! If you are saving a bitmap from original work that may be scaled down or edited later, then I'd recommend using a lossless format like tiff, since every time you resize a jpeg you are reducing the image quality.

There *are* ways of transforming jpeg files in particular ways losslessly (rotate, flip, crop, etc). A number of bitmap editing programs have included features or have plugins to do so - see http://sylvana.net/jpegcrop/losslessapps.html for a list. An example stand-alone application is JpegCrop at http://jpegclub.org/ .


Regarding the gif scaling:
In theory, saving a scaled-down .gif from a vector ought to yield better results than saving a scaled-down .gif from a bitmap representation of that vector, since you have the original line to work with and not a pixelated version of it. I believe the example below shows this to be true for Xara X.

I drew a simple, nearly diagonal line and exported it as a .gif at 100% and then again at 75%. I then imported the 100% bitmap and re-exported it at 75%. Before assembling the composite image below, all three gifs were scaled up 500% without anti-aliasing using a simple bitmap editing program (IrfanView) to reveal the individual pixels.

Notice that the 100% and 75% bitmaps saved from the vector both have a certain sharpness in that a number of the central pixels are quite dark (the line was drawn black). The gif that was re-exported has lost the dark pixels due to pixel averaging and therefore does not appear to be as sharp.

- Pete

[JF Slater]

The problem for me arises with thumbnails for the web which some-one else has made. Will check out your jpeg link.

Risto, I love the look of your new website. I can't wait until it's ready!
I thought the blue images with coloured rollover were a brilliant idea.

Jess

[mckinney]

Just noticed I mis-typed above when I said:

"every time you resize a jpeg you are reducing the image quality".

I suppose this is true, but the point I meant to make is that "every time you re-save a jpeg you are reducing the image quality"

Also, the JpegCrop tool I mentioned is freeware.

- Pete (who waited longer than the allotted 60 minutes to proof-read his message....) [img]/infopop/emoticons/icon_redface.gif[/img]

[RTK]

Pete, thanks for taking time going through all that for me. I think it makes sense that the quality would be better when exporting from vectors. The anti-aliasing would be "adapted" for that particular size of the objects.

Thanks, Jessica. I have to tell you that the blue thumnails are all gone... now I have something more me. The site will be a mix between the orginal and some ideas from rgremill's and Gary's commments.

Risto

diri@videotron.ca

[netspotz]

When you are creating graphics and haven't a clue as to what format you wish to save them in the future, do yourself a favor and create a .tif directory under your main directory, then always save the graphic as a .tif at FULL EVERYTHING--no compression--NO NOTHING!

Always save your graphic to your website's "graphics" directory as a last result by importing it into XaraX and then re-exporting it in the final format. You have a lot of control this way and can sample the various file sizes and looks. Plus, if you change your mind later, then you will always have your original .tif.

[pduggan]

<BLOCKQUOTE><font size="-1">quote:</font><HR>When you are creating graphics and haven't a clue as to what format you wish to save them in the future...<HR></BLOCKQUOTE>

Keep the .xar! Any bitmaps you've used in its creation will still be in whatever format they started in. [img]/infopop/emoticons/icon_smile.gif[/img]



Peter</p>



Peat Stack or Pete's Tack?</p>