Quality of Captured Image

[LiDale]

I use SC each and every day. Thanks so much for the support with this fantastic product. I am probably ok, but just one question. I use SC to save text and images sent to me from my family. Most of the time it is captured from an email and from time to time it is captured from a web site. I understand the quality of the captured image relies on the quality of the image I am attempting to capture. I take each captured image and post it, along with family comments, in a blog type site. Sometimes for printing and sometimes just for reading for all other family members. I basically use SC with most all default settings and it does a great job. I just want to insure I have the 'settings' correct to give me the best possible color and resolution of the captured images and/or text.

Sorry for rambling, my question is "what settings / options should I have SC set to insure the output image (jpg, pdf and png) is the highest color and resolution possible."

Thanks in advance for your time.

[tomos]

Hi LiDale,
I think png is the default filetype - this is the best quality for screenshots anyway. Avoid jpg completely here (files are smaller but quality is worse).

You mention PDF - are you using PDF anyway? - or are you asking if it's better quality than the others? If the latter, again, I'd say just stick with the png filetype.

Here's my settings -



The dpi and colour are default - no need to change them (dpi may vary according to your monitor).

[mouser]

What tomos said.  As long as you save in PNG format (which SC uses by default) your images will be 100% perfect, exactly what you see on screen.
It's only when you save in a "lossy" format like jpg that files can degrade in quality from the original.

[Jibz]

If the size of the image file matters, it can be a good idea to use one of the many png optimizers available. Here is an example to illustrate this:

Saved as 24 bpp png from SSC, 240k:



Optimized version, 149k:



Saved as 8 bpp png from SSC, 72k:



Optimized version (note that it also has better colors), 32k:

[tomos]

^ 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...

[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)

• 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 .
• 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)

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 artifacts^w 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:

Spoiler

24 bpp PNG @39k:



JPEG @40k:



8 bpp PNG @20k:



JPEG @20k:

[tomos]

Learning here

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
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)

That depends a lot on the contents.

-Jibz (February 26, 2014, 01:07 PM)

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.

[Jibz]

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

-tomos (February 26, 2014, 01:28 PM)

For the examples above, I was using RIOT, which has a simple interface (and is used as a plugin by IrfanView).

It looks like it is a bit hehind other tools though, here is the 47k PNG produced by pngquant:



There's only slight banding in the big gradient, and there is visible dithering, but otherwise it's impressively close to the original.

[tomos]

It looks like it is a bit hehind other tools though, here is the 47k PNG produced by pngquant:

-Jibz (February 26, 2014, 02:31 PM)

all I need is a GUI ;-)
but I do have IrfanView installed (thanks for the info).

[mouser]

Maybe someone can make a SC tool file for one of these png compressors so it's easier to access from SC tool menu?

[mouser]

My coarse rule of thumb for file formats:

Photographs: JPG (usually i use quality options of 90-95% in whatever program i'm using)
Anything else: PNG

[lanux128]

i would like to add PngGauntlet to the list of PNG compressors. recommended by [user]justice[/user] here.

Spoiler

[Jibz]

Since we've discussed tools to optimize image size and quality here, I thought I'd mention Mozilla's recently introduced JPEG optimizer project mozjpeg.

[Jibz]

mozjpeg 2.0 has been released

Thanks to CMake it built without problems on Windows here .

[tomos]

For the examples above, I was using RIOT, which has a simple interface (and is used as a plugin by IrfanView).

-Jibz (February 26, 2014, 02:31 PM)

this was updated in 2016 - there may be better out there in terms of compression, but it has a good interface:

Quality of Captured Image

it's slow with hi-res files, but does offer to reduce resolution as you open the file.
I'm happy, e.g. the file in image there got reduced from 280 to 85KiB
[note I didn't reduce the resolution of the file]

(Note that higher compression makes very little difference but takes much longer.)