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i have a bunch of images which are way too big i need to decrease their size from 30 kb to 10 or 5 kb without loosing quality. I tried to change the dpi and pixels with no succeed. The images got blurred, and as they have text i can't read anything after the changes. Is there anyway i can accomplish this without loosing quality? I have almost a dozen images in my application.

Thanks in advance and have a nice day.

madcoderz
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    What file format are the images in? What is the nature of the images (are there large blocks of a single colour?) What are the dimensions of the images? – Alex Howell Jan 12 '11 at 12:36
  • They are in png i heard that i can change them to jpg but the difference is not big – madcoderz Jan 12 '11 at 12:38

4 Answers4

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for batch resizing I use IrfanView (despite it's "lite-ness" it's very powerful). It has a nice batch dialog, with a lot of options.

If you're working with png files try using better compression, and/or different color depth settings (if you're not using transparency you could try converting them to jpeg, although you might lose some quality)

changing color depth/range/compression might not affect image quality (not visibile anyway, if used with moderation) and it will decrease the size of the picture - in most of the cases anyway

if you want to stick to Gimp (I never personally used it), it should have some export features where you can select some settings for the image, like format and options

Andrei S
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You cannot leave out data without reducing quality. Data has meaning.

You may try to use improved compression, pngcrush is the tool that automatically tries several approaches for you and picks the best.

Reducing colour depth will reduce the file size (while reducing colour quality). You can also turn on dithering in some image editors, but that's another loss in quality.

If your image has photographic content rather than graphical, convert to JPEG and use the JPEG quality settings, experiment with them a bit.

foo
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  • Dithering can actually make a file bigger, since the lossless compression will be less effective. – Mark Ransom Sep 16 '11 at 21:36
  • True, depending on file format - for JPEG, it won't, but for PNG it generally does make the file bigger. – foo Oct 04 '11 at 01:43
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    even for JPEG it might increase the high-frequency components and result in a larger file. I've seen it happen. – Mark Ransom Oct 04 '11 at 02:24
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It seems that if I have a large png of 2500px wide and I want to resize it down to 100px wide, If I scale the image all at once the the desired size the image becomes way to distorted to use.

However If I scale the image in small increments of 200 pixels and repeat until you reach the desired length the image does not get as distorted. So if Im at 2500px then I would scale the image to 2300px then to 2100 and so on. The smaller the scale the less distortion.

Mike
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Any resize method will have some loss, no matter how small. Following steps will make you lose quality.

steps for a single layer

    layer->scale layer
    image->scale image
    image->fit canvas to layer
    file->export as

steps for multiple layers

    layer->new layer group
    move all layers to layer group
    select layer group
    layer->scale layer
    image->scale image
    image->fit canvas to layer
    file->export as
cppRohit
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