After upgrade to 7.4.2 Build 4650, it began to seem to me that all the pictures in my >10-years project are a bit muddy/soapy. I looked inside CHM: the sizes of the images are set in inches in the IMG embedded style - I guess this is the reason.
You can change this the easy way by going to Configuration > Publishing Options > HTML Help > HTML Export Options and turning off the option for making your CHM compatible with high-resolution displays. That's not such a good idea, however, because then your CHM will only look reasonably good on old computer displays and old laptops. The Microsoft CHM system is ancient and internally massively obsolete (it hasn't been updated or even maintained to fix bugs since it was originally released with Windows 98). The new code generated for it by Help+Manual does everything it can to force it into the modern world, including handling images as well as possible.
Inches are used because those are the only units in CHM that allow something coming close to responsive adjustment. Your images are looking very slightly unclear because you have defined them with absolute dimensions in your old project (physical size) and there will always be a slight rounding error when converting to inches. You can avoid this problem by making the images genuinely responsive. To do that, double-click on the image in Help+Manual and in the Display Size: option choose "% of page width, maximum is physical width". If there is room for the image it will then be displayed at exactly 100% and will only be scaled down if it doesn't fit.
Important: If the image is in a table cell then "page width" refers to the dimensions of the cell, not of the page.
In the long run, however, you need to abandon the ideal of ever seeing images at an exactly 1:1 ratio ever again. That just doesn't happen any more. Displays no longer work with physical pixels because the physical pixels are now way too small. Except on really ancient displays, they are almost always grouped together to form "virtual" pixels, and how that is done differs from display to display -- some physical pixels are also oblong instead of square. This is further complicated by the display zoom of the operating system, which can be adjusted individually, plus the zoom setting of the web browser. Put all that together and the chances of any user seeing your images at an exact 1:1 representation of their original pixels on the pixels of the screen, even the virtual pixels, is very very remote.
This means that there is always going to be some scaling of almost any image displayed on any computer monitor. This is fine for photographs and even most graphics, which are now almost always generated larger than they need to be, which gives adequate leeway for scaling/zooming with acceptable quality. It's a problem for screenshots made on low-resolution screens because there are no high-resolution versions to be got. You can get around this to some extent by making your screenshots on a 4K screen and scaling them down, but that gives you larger files. Personally, I just don't worry about it any more: I use a low-resolution second monitor next to my main 4K monitor for making my screenshots and just accept that they're usually going to be a little unclear. They're still fine for reference purposes and that's all that really matters.
Regards,
Tim (EC Software Documentation & User Support)
Private support:
Please do not email or PM me with private support requests -- post to the forum directly.
