Change File Size on Photoshop?

Not sure whatchyer problem is - have you tried resizing the image with Irfanview or PhotoShop and looking at the results?

There are a number of image filesize reduction techniques, but yeah 6k is pretty small and things like saving different parts of a jpg at different compression levels isn't gonna help much with an image of so small dimensions (max 90x100 px on able2know). For any image with those dimensions though, you can probably get the filesize smaller (and at a higher visual quality) as a gif than a jpg, if you know what you're doing (certainly not so with larger, photorealistic images). But you can always save in both formats and compare the size as well as the visual quality you had to sacrifice to get that size.

A couple pointers about saving gifs as small as possible (ordered by impact on filesize for the average gif):
- With animated gifs, share a single color palette across all frames, and remove any pixels within a frame that have not changed since the last frame.
- Reduce the color pallete as much as possible (i.e. don't use the available 256 color pallete if it looks okay with less).
- Don't use any dithering.
- Some programs that save gifs (especially animated gifs) like to save their company name and copyright information as a hidden comment in the gif. Turn off the option, or if that's not possible don't use the application.
- Don't allow transparency if you don't use any.
- Don't enforce saving black and white into the palette if you don't use any.

Also note that horizontal repitition compresses better than vertical repitition in gifs...e.g. a gif with horizontal stripes will be smaller than with vertical stripes. This probably won't help you get an existing image's filesize down, but it can help if you're aware of it during the image creation process.

For a jpg of that size, basically you've got the quality adjustment slider and the knowledge that more visual complexity equals larger file. With a larger jpg, you can get better results at a better visual quality out of fancy options like compressing differnet parts of the image at different quality levels as I mentioned earlier.

Photoshop can handle everything I mentioned except the stuff about animated gifs.


Edit: ordered by impact

Wow ok that points me in the right direction. Much appreciated.

You're welcome.

Some tips for JPGs (which I didn't really get into because I wouldn't recommend saving almost any 90x100 px or smaller image (A2K's allowed avatar size) as a JPG as long as you know how to set a GIF color palette and prevent dithering)...

- Adjust the quality to the minimum you find satisfactory.
- As mentioned earlier, you can save parts of a jpg at differing quality levels....these controls in Photoshop are under Save for Web. This will allow you to save parts that compress well anyway (i.e. sections with less complexity) at a higher quality than the rest, resulting in a better-overall looking image at a smaller filesize).
- Don't save an ICC color profile with the image.
- Don't let photoshop save a thumbnail with the image (you may need to edit Photoshop's file handling options in order to disable this).
- Choose Baseline Optimized rather than Baseline Standard as your jpg format option. Baseline Optimized offers less compatibility but I believe all modern web browsers support it.
- Use 8 Bits/Channel (usually the default) rather than 16 bits. 8 bits for each of the RGB color channels equals 24 bit color equals roughly 16.8 million possible colors.
- Use the RGB (usually the default, and better for screen display anyway) rather than CMYK (often preferred by professional printers, as ink comes in CMYK) color channels.
- If you have a grayscale image, manually switch to using grayscale as your color channel. (If your image is truly black and white or a limited number of shades of gray, odds are you can get if smaller as a gif.)
- Photoshop doesn't let you save layers or custom channels with a jpg, but it does keep vector paths (in the Paths panel). Remove any that exist before saving as a jpg.
- Don't add metadata (File > File Info), and remove any that exists.

Hope this helps. My knowledge of jpg and gif filesize reduction comes pretty much entirely from testing and my own optimizations for the web, as I've never found a good tutorial on the subject.