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Quality of Captured Image

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Jibz:
^ I'm pretty confused there Jibz :-[


* 1) I dont see any option to change bpp in Screenshot Captor(?)
* 2) I presume the default in SC is 24bpp?
* 3) all screenshots say 24bpp in the statusbar, yet you label #3 as 8bpp
* 4) what are the k numbers - I know k is a thousand ;-) but is it number of pixels? (240k etc)
* 5) is the idea that the optimisier reduces the image size, but keeps the quality?
Or is it simply to improve quality of lower quality images (#3 =>#4 above)?
I dont see any difference between images #1 & #2...-tomos (February 26, 2014, 10:30 AM)
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* 1) It took me a while to find this option as well. To me, the logical thing would be if there were some options while saving, or if the "Image File Format" tab in the preferences changed, oh I don't know, perhaps the image file format? But it doesn't, instead you have to go into the menu SpecialFX2 and select "Adjust color depth and DPI" to reduce the number of colors.

* 2) As per 1) above, quite ;D.
* 3) I can see how this might be confusing :-[, I opened a 24 bpp image in an image viewer, and took a screenshot of the entire image viewer window. The four images are the same screenshot saved in different ways.
* 4) They are image file size in kilobytes.
* 5) In the case of saving as 24 bpp (example 1 and 2 above), the image quality is the same, so you save space. In the case of reducing the color depth to 8 bpp (example 3 and 4 above), the image quality is better and the file is smaller when the color depth is reduced in an outside program.
I chose this image deliberately because it is "hard" to convert to 8 bpp and get a decent result due to the gradients. Screenshots of application windows, which usually consist of white background with text and a few buttons generally loose little quality from being converted to 8 bpp, and if you are sending several screenshots over e-mail it can make a difference if they are 1 mb each, or 200 k :).

Vurbal:
If you want to reduce the file size JPEG compression is generally a better option, quality-wise, than reducing the color depth.

Jibz:
If you want to reduce the file size JPEG compression is generally a better option, quality-wise, than reducing the color depth.
-Vurbal (February 26, 2014, 11:23 AM)
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That depends a lot on the contents.

JPEG is very good at compressing the type of data you see in photographs, but quite poor at reproducing text due to compression artifactsw on high-contrast details.

Here is the same screenshot, compressed to a JPEG file of the same size as the 8 bpp png above (32k):



As you can see, it handles the gradients better, but the text, icons, and the bright lines, show JPEG artifacts.

And this was a type of image that PNG has trouble with. If you take a screenshot of something like the configuration dialog from Screenshot Captor, you can really see how much better PNG handles these kinds of images:

Spoiler24 bpp PNG @39k:



JPEG @40k:



8 bpp PNG @20k:



JPEG @20k:

tomos:
Learning here :Thmbsup:

I'm curious -- what software did you use Jibz, in the examples above?

Example #2 is ~40% smaller than example #1 - I dont see any loss of quality :up:
That could be very helpful occasionally. Cant imagine myself going to the trouble of reducing the bit depth, but who knows, could be helpful too someday.

Vurbal:
If you want to reduce the file size JPEG compression is generally a better option, quality-wise, than reducing the color depth.
-Vurbal (February 26, 2014, 11:23 AM)
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That depends a lot on the contents.
-Jibz (February 26, 2014, 01:07 PM)
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That's very true. PNG, being just a compressed bitmap, is much better at spatial precision and of course being lossless makes it completely (compression) artifact free.

Of course, depending on the software you compress with, JPEG can also be tuned to avoid or obscure compression artifacts. OTOH having lots of sharp edges (like text) always means either ugly artifacts or poor compression.

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