> Posted by: "David Riecks" da...@riecks.com davidriecks > > A screen capture will likely have > > poorer quality than the file it displays.
> Ed:
> What documentation do you have to support this claim?
I may be wrong, but was assuming that if you displayed a higher quality jpeg on a monitor, that the full gamut and file quality does not translate to the screen. Do you think most monitors being used today show 100% of what is in a file, regardless of the PS quality level chosen?
>I may be wrong, but was assuming that if you displayed a higher quality jpeg >on a monitor, that the full gamut and file quality does not translate to the >screen. Do you think most monitors being used today show 100% of what is in >a file, regardless of the PS quality level chosen?
Okay, there's something getting lost in this discussion: A screen capture has nothing (or very little) to do with the quality of your monitor. What a screen capture does is record what is in the memory of your video board. And, that's the data from whatever image file you are displaying.
-- Ernest
-- Ernest H. Robl, Durham,NC,USA Stock photos; photojournalism; writing Specializing in transportation and travel subjects for more than 35 years. mailto:e...@mindspring.com Phone +1 (919) 401-9480 Fax 402-0721 Web site: http://www.robl.w1.com "I'd rather be on the train." Intermodal Container FAQ: http://www.robl.w1.com/Transport/intermod.htm
Ed Verkaik wrote: > I may be wrong, but was assuming that if you displayed a higher quality jpeg > on a monitor, that the full gamut and file quality does not translate to the > screen. Do you think most monitors being used today show 100% of what is in > a file, regardless of the PS quality level chosen?
Ed:
I just ran a test, as I wanted to test your assumption since I didn't know either.
I found a page of my website with an image that contained fairly bright saturated colors that I could measure and compare. I then did a series of screen grab from Microsoft Internet Explorer on Windows, and Safari and Firefox on Mac.
I then opened up the un-profiled jpeg (originally was sRGB if I recall) from my site (the original file that was being displayed in the screen grabs), and dragged and dropped it on to each of the screen grabs, and then set the layer mode to "difference."
On the windows version, the file completely blacked out, meaning that the color values and edge definition were exactly the same.
On both of the mac screen grabs, most of the image blacked out, though there seemed to be issues with getting the file to line up directly on top of each image. Thus there was a small amount of edge detail showing. My guess is that this may be due to the slight differences in base screen resolution between mac and windows. I'll put together a composite of these if anyone is interested in seeing what I'm talking about.
As a double check I used the color sampler tool in Photoshop and tried to measure the same color patches including a few elements from the website. Without exception, they were all within 1 or 2 RGB point values, which I would attribute to my not being precise enough in measuring the same area of the image. I saved these values in an Excel spreadsheet if anyone wants to see that, just let me know.
This would be much simpler to verify with a series of color and gray patches and that's what I would use if I was going to repeat this as a "scientific" test.
So, unless you are talking about posting preview images that are in another colorspace such as Adobe RGB, I don't think your assumption holds true.
On 1/9/07 10:52 AM, "David Riecks" <da...@riecks.com> wrote:
>> >On the windows version, the file completely blacked out, meaning that > the color values and edge definition were exactly the same.
>> >On both of the mac screen grabs, most of the image blacked out, though > there seemed to be issues with getting the file to line up directly on > top of each image. Thus there was a small amount of edge detail > showing. My guess is that this may be due to the slight differences in > base screen resolution between mac and windows. I'll put together a > composite of these if anyone is interested in seeing what I'm talking
This is quite interesting and I wouldn¹t have expected this result. My assumption was that, as on the PC, the file would be pixel-for-pixel, level-for-level, identical. Thanks for doing this test. I would be interested to hear if you come up with any firmer conclusions about what is happening in the mac to account for this behavior.
>> >So, unless you are talking about posting preview images that are in > another colorspace such as Adobe RGB, I don't think your assumption > holds true.
Even though the image may be displayed in the wrong color space, a screen capture in no way captures a damaged file (at least on a PC!). The user simply has to apply the correct profile or any other profile that looks ³correct² or pleasing.
Jonathan Clymer
[Non-text portions of this message have been removed]
> > I may be wrong, but was assuming that if you displayed a higher > quality jpeg > > on a monitor, that the full gamut and file quality does not > translate to the > > screen. Do you think most monitors being used today show 100% of > what is in > > a file, regardless of the PS quality level chosen?
> Ed:
> I just ran a test, as I wanted to test your assumption since I didn't > know either.
A screen capture on a Windows machine will capture the exact contents, pixel for pixel, that one sees on the screen. The Windows GDI has its own function to do this, BitBlt.
I have no idea how the Mac does it, but I would expect it to be very similar.
If one is really worried about theft of their images, one can display them in a movie file. Many (most?) PCs today have graphics cards with some sort of hardware accelerator which renders the movie in a different part of video memory that will not be captured by BitBlt.
You can try this yourself. Go to CNN.COM, play any of the videos, then press PrtScr. Go to PAINT, then press Paste (Ctrl-V).
If your video accelerator is on, you'll see a perfect screenshot with blacked out video. If the accelerator is off (or if you don't have it on your PC), you'll see whatever video frame was playing when you pressed PrtScr.
Most PC users are not aware of this and anyone with hardware acceleration usually has it on by default. For the truly paranoid, this would probably be more effective than gimicky "encryption" software that preys on the technologically ignorant.
I should be clear that there are ways to capture movie frames from even an accelerated card using specialized screen capture software. I think SnagIt does it. But many simpler software that use the base BitBlt function will not work.
