RIOT Forum

Radical Image Optimization Tool

1. Alan Drabke
   Member

   (1) My first virus free PNG file attachment is a cover image I made in Inkscape.
   I set the (File -> Document Properties) document size to: A5, 148 x 210 mm.
   Then I exported the work to a PNG file at 300 dots per inch. As you can see,
   this slims the final product down to 427 kilobytes, and the image is nice and
   sharp.

   (2) My second attachment is a copy of the PNG file I scaled to 600 x 900 pixels in GIMP
   and then saved as a jpeg. In this case, the image trimmed down to 241 kilobytes
   and it stayed sharp and crisp.

   (3) My third attachment is a copy of the PNG file I scaled to 600 x 900 pixels in RIOT
   and then used the 'Compress to Size' function to bring it down to 62 kilobytes. This
   is the best 62 kilobyte image I can produce. As you can see, it is not as good as
   the previous two copies.

   I have to, must be able to, end up with a 600 x 900 pixel file weighing in at 62
   kilobytes. That's the standard set for me by the people at Amazon. If I want to
   publish a book as a Kindle download, it has to come in line with these numbers.

   It seems to me that jpeg files are supposed to support compression ratios of 10
   to 1 without a loss of image quality. If that's the case, what am I doing wrong?

   Posted 12 years ago #

2. luciansabo
   Key Master

   I am pasting you the answer sent by email:

   If you need 600x900, there is a problem because scaling proportionally needs 910 as height, so in fact you have a 600x910 pixels images.

   Short story: I am attaching you the image compressed at 62 KB and provide you some tips.

   Long story:

   For example, using your image I made the following settings:
   - resize using the lanczos filter to 600x910 px
   - select JPEG
   - turn off jpeg chroma subsampling by selecting Chroma: none
   - set jpeg encoding to Progressive
   - click on Compress to size and enter 62
   - the result will be an image with a JPEG quality of 51 having 61,46 KB which looks very similar to the original

   If it wasn't the globe, you could have chosen PNG with a 256 colors palette and a best compression.

   As you can see, RIOT is a powerful tool , but you need time to get the most out of it. If you use it at work please consider a small donation to support further development.
   The future version will contain an automatic optimization mode which will automatically choose the most suitable settings for your images and allow you to tweak them manually also.

   JPEG compression of 10:1 without quality loss is not possible, simply because JPEG is lossy even at 100% quality. JPEG only can produce non-noticeable image quality loss for the naked eye at quality settings over 80, with a low chroma.

   A quick note about chroma. You should set Chroma to none or low. Set it to none if you have few colors and to low if you have many colors to obtain the maximum similarity with the source image. Then play with the quality slider until you are happy with the result.
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   Posted 12 years ago #

3. Alan Drabke
   Member

   Do I understand the issues? It seems to me you are telling me that a PNG file offers the most flexibility. That PNG files have the widest possible dynamic range. Much better than jpeg files. Is that correct? Also, I'll be working with your suggestions for a week or two.

   Posted 12 years ago #

4. luciansabo
   Key Master

   PNG has a lossless compression scheme. So, when talking about image quality, yes PNG is the clear winner, but JPEG creates smaller files for photographic images. You should read more about JPEG and PNG here then return if you have some questions.

   Posted 12 years ago #

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