how to reduce PNG file size ?

[Tobias Jung]

I just wrote: > Without visible loss in quality, that should be impossible. For GC or > any other tool. To be more precise, that's impossible IF it really had to be a PNG image. As Tony just pointed out, it can be reduced to that size if it's a JPG image -- which has a certain loss in quality but probably you won't notice. Regards, Tobias

[Zalman Lazkowicz]

True, I realize that. I did a test on CompressPNG.com, and the resulting image was excellent. I didn’t notice much loos in color. But I don’t need this type of compression on a daily basis. Just today. so it was ok. Thanks to all!!!Zal On Apr 16, 2015, at 4:05 PM, 'Tobias Jung' newsgr@tobiasjung.net [gcmac] <gcmac@yahoogroups.com> wrote:Zalman Lazkowicz zlazkow@yahoo.com [gcmac] wrote (Thu, 16 Apr 2015 14:42:19 +0300):> this is 11 mb. I need to make it less than 4 mb, without visible loss in> quality.Without visible loss in quality, that should be impossible. For GC or any other tool.As Tony Jackson suggested, you can reduce the number of colours (that's one of the things that those online tools you're mentioning do). That'll result in a file of about 2 MB, but of course, that will be visible, though to a lesser degree than you might suspect.Kind regards,Tobias Jung

[Tony Jackson]

Attachments : Re: [gcmac] how to reduce PNG file size ? Thanks Thorsten, but I need this in PNG. There are some sites that do that, but it takes quite some time uploading. Thought maybe GC has something like that, sort of compressor. In case it is helpful, you can convert it to a .gif, which is a similar, lossless format, but on this image it is much smaller.  (Convert it back to .png and it is big again!) Why does it have to be a .png? Here it is in .png with 32768 colours, instead of millions.  This gives 4.7 MB. or in 256 colours, it is 1.8 MB, but a bit less true, perhaps? -- Tony Jackson, Devon, UK.

[Zalman Lazkowicz]

Thanks Tony,I need png for Cafepress. It is not must, but recommended type, because it provides a better image quality, smoother, according to CP. I can of course use JPG, and will probably be using jpg, despite their recommendation. These posters files are really big, so I have no choice, and will be using jpg.  Zal On Apr 16, 2015, at 3:08 PM, Tony Jackson tony@you-me-and-us.com [gcmac] <gcmac@yahoogroups.com> wrote:Thanks Thorsten, but I need this in PNG. There are some sites that do that, but it takes quite some time uploading.Thought maybe GC has something like that, sort of compressor.In case it is helpful, you can convert it to a .gif, which is a similar, lossless format, but on this image it is much smaller.  (Convert it back to .png and it is big again!)Why does it have to be a .png?Here it is in .png with 32768 colours, instead of millions.  This gives 4.7 MB.<Yosemitec.png>or in 256 colours, it is 1.8 MB, but a bit less true, perhaps?<Yosemitecd.png>-- Tony Jackson,Devon, UK.<Yosemitec.png><Yosemitecd.png>

[Tony Jackson]

Hi Zal, >I need png for Cafepress. It is not must, but recommended type, >because it provides a better image quality, smoother, according to >CP. I can of course use JPG, and will probably be using jpg, despite >their recommendation. These posters files are really big, so I have >no choice, and will be using jpg. Where did the original file come from? At 150 dpi it will not be very sharp at 18" tall. I would normally say that 300 dpi is a minimum for acceptable clarity, but that one could achieve a much smaller file size at this size and 300 dpi. Was this originally a scan, which was then jpeg-compressed? If you can get to the original scan it should be possible to improve on what you have, bur remain below 4 MB. I don't know why the .gif was so much smaller, but this may well be acceptable, and will not need compressing further, yet holds the same information a your original (I think). Best, T. -- Tony Jackson, Devon, UK.

[Zalman Lazkowicz]

Hi Tony,I don’t have the original scan. When I purchased it, I didn’t know what was the dpi. But that’s ok, I’ll just use a smaller size, for smaller items.All the best,Zal On Apr 16, 2015, at 4:42 PM, Tony Jackson tony@you-me-and-us.com [gcmac] <gcmac@yahoogroups.com> wrote:Hi Zal,>I need png for Cafepress. It is not must, but recommended type, >because it provides a better image quality, smoother, according to >CP. I can of course use JPG, and will probably be using jpg, despite >their recommendation. These posters files are really big, so I have >no choice, and will be using jpg.Where did the original file come from? At 150 dpi it will not be very sharp at 18" tall. I would normally say that 300 dpi is a minimum for acceptable clarity, but that one could achieve a much smaller file size at this size and 300 dpi.Was this originally a scan, which was then jpeg-compressed? If you can get to the original scan it should be possible to improve on what you have, bur remain below 4 MB.I don't know why the .gif was so much smaller, but this may well be acceptable, and will not need compressing further, yet holds the same information a your original (I think).Best, T.-- Tony Jackson,Devon, UK.

[ilmionomeedjango]

IIRC gif can do LZW compression (which is lossless) and has a max color palette of 256 colors (color reduction is always lossy)But png also uses a ZIP-like compression, which is almost as good as LZW (depending on the content). So the size difference is likely because of the 256 colors.By the way there are excellent tools for png-size reduction:ImageAlpha (http://pngmini.com) and ImageOptim (https://imageoptim.com).ImageAlpha also does color table reduction (you can choose between 256 down to 2), ImageOptim is lossless (it cleans up the internal png data and refines the lossless compression).You should use it in the order 1) ImageAlpha 2) ImageOptim.GC can also save pngs with a reduced 256 colors table (checkbox "lossy compression" in the png settings).-- Tom