Images in Pictures folder

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Images in Pictures folder

Unread postby Gillian Tronson » Fri Mar 02, 2018 2:22 pm

Please can someone explain: I had a lot of .bmp images that I was using in my project which was compiling to a chm file of size 4600kb
Some of them were very big and I thought that by replacing them with much smaller .png files I would reduce the size of the .chm file.
But it has actually grown to nearly 8000kb.
Is there some setting I am missing?
Many thanks, Gillian
Gillian Tronson
Posts: 9
Joined: Wed Nov 15, 2017 7:30 am

Re: Images in Pictures folder

Unread postby Tim Green » Fri Mar 02, 2018 2:56 pm

Hi Gillian,

Paradoxically, using BMP files will often get you the smallest possible output file size. This is because BMP is almost never used directly, and even when it is (in PDF) it can be compressed very efficiently. It is also ideal for converting to other formats like PNG and JPEG, because since it is lossless and doesn't have any compression there is no additional "fuzziness" from existing compression, which makes compression much harder. PNG files are just inserted in your output as they are, and cannot be compressed any further. Also, depending on the graphics program you are using, PNG files will often be quite a lot larger than other formats, particularly if they have more than 256 colors.

  • You will generally get the smallest possible files with BMP using 256 colors. They will compress efficiently and can be converted optimally to any other format.
  • If you insert PNG directly they will not be compressed further, so you need to check the size before using them, adjusting your graphics program's save settings if necessary.
  • You can find the conversion options for graphics in CHM and WebHelp in Configuration > Publishing Options > HTML Help/WebHelp > HTML Export Options. Converting everything to PNG will give you the best quality but larger files. The best compromise is usually the option to convert True Color to JPG and 256 colors to GIF, and then experiment with the JPEG compression setting to find the best compromise between file size and quality.
  • Only use PNG for PDF output if you absolutely must have images with alpha transparency. Otherwise, BMP is generally a better choice there as well. You can find settings for image compression for BMP in Configuration > Publishing Options > Adobe PDF > PDF Options
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Re: Images in Pictures folder

Unread postby Gillian Tronson » Sat Mar 03, 2018 1:41 pm

Thank you so much Tim - eish will have to reconvert to .bmp
Gillian Tronson
Posts: 9
Joined: Wed Nov 15, 2017 7:30 am

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