if you use Save For Web in photoshop, a GIF file will always be smaller than a PNG-8 file of identical options. Now...this isn't any good reason to be using PNGs if a GIF does the exact same thing.
Anyway I went out searching for how to optimize pngs and found the program <a href="http://pmt.sourceforge.net/pngcrush/" target="_blank">pngcrush</a>... here's its startup options:
usage: pngcrush [options] infile.png outfile.png
pngcrush -e ext [other options] files.png ...
pngcrush -d dir [other options] files.png ...
options:
-already already_crushed_size [e.g., 8192]
-bit_depth depth (bit_depth to use in output file)
-brute (Use brute-force, try 114 different methods [11-124])
-c color_type of output file [0, 2, 4, or 6]
-d directory_name (where output files will go)
-double_gamma (used for fixing gamma in PhotoShop 5.0/5.02 files)
-e extension (used for creating output filename)
-f user_filter [0-5]
-fix (fix otherwise fatal conditions such as bad CRCs)
-force (Write a new output file even if larger than input)
-g gamma (float or fixed*100000, e.g., 0.45455 or 45455)
-iccp length "Profile Name" iccp_file
-itxt b[efore_IDAT]|a[fter_IDAT] "keyword" "text"
-l zlib_compression_level [0-9]
-loco ("loco crush" truecolor PNGs)
-m method [0 through 200]
-max maximum_IDAT_size [default 8192]
-nofilecheck (do not check for infile.png == outfile.png)
-n (no save; does not do compression or write output PNG)
-plte_len n (truncate PLTE)
-q (quiet)
-reduce (do lossless color type or bit depth reduction)
-rem chunkname (or "alla" or "allb")
-replace_gamma gamma (float or fixed*100000) even if gAMA is present.
-res dpi
-save (keep all copy-unsafe chunks)
-srgb [0, 1, 2, or 3]
-text b[efore_IDAT]|a[fter_IDAT] "keyword" "text"
-trns_array n trns[0] trns[1] .. trns[n-1]
-trns index red green blue gray
-v (display more detailed information)
-version (display the pngcrush version)
-w compression_window_size [32, 16, 8, 4, 2, 1, 512]
-z zlib_strategy [0, 1, or 2]
-zmem zlib_compression_mem_level [1-9, default 9]
-zitxt b[efore_IDAT]|a[fter_IDAT] "keyword" "text"
-ztxt b[efore_IDAT]|a[fter_IDAT] "keyword" "text"
-h (help and legal notices)
-p (pause)
anyway...using this program I was able to save 25-30% size from all my PS-generated PNGs, and every one was smaller than the corresponding GIF.
You can get the OS X binary here
<a href="http://us.dl.sourceforge.net/sourceforge/gnu-darwin/direct_download/packages/ppc/graphics/" target="_blank">http://us.dl.sourceforge.net/sourceforge/gnu-darwin/direct_download/packages/ppc/gra phics/</a>
Oh also...Save For Web and normal photoshop save as (in PS 6-7) makes PNGs that are too dark. Using the "-rem alla" option fixed this problem in all my pngs. Not sure if this is a gamma issue or ICCP issue.
<small>[ 06-14-2002, 03:38 PM: Message edited by: OoklaTheMok ]</small>
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