Working with Images

Thu Feb 7 06:55:18 PST 2008

No problem sir, we are all human. Thank you for being a gentleman and replying to my post. 
Rick

  _____  

	From: Dennis Brunnenmeyer [mailto:dennisb at chronometrics.com] 
	Sent: Wednesday, February 06, 2008 2:11 PM
	To: TEI Melanson, Richard; framers at lists.frameusers.com
	Subject: RE: Working with Images

	Rick...

	You are very correct about my brashness. My apologies to all of you. I was anxious to try and squelch some misconceptions and got carried away. David Creamer was particularly incensed with me because he thought I was aiming the whole rant at him. This was not the case, of course, but I can see his point. in the meantime, he and I have called a truce, as we both have better things to do.

	Dude...
	******************************************
	At 06:26 AM 2/6/2008, richard.melanson at us.tel.com wrote:

		Dude, you may be the expert on this, and the info you supplied in your response is so good I am saving it, but how about a little respect for everyone on the list. I believe whatever anyone said in an attempt to help they believed to be accurate and helpful. To say and I quote you "Well, I've had enough of this nonsensical babble. None of you seem to understand what you are talking about when it" is a little strong. Life is too short, take a deep breath and enjoy!!
		Rick

		-----Original Message-----
		From: framers-bounces at lists.frameusers.com [ mailto:framers-bounces at lists.frameusers.com <mailto:framers-bounces at lists.frameusers.com> ] On Behalf Of Dennis Brunnenmeyer
		Sent: Tuesday, February 05, 2008 2:37 PM
		To: David Creamer; framers at lists.frameusers.com
		Subject: RE: Working with Images

		Rant begins...

		Well, I've had enough of this nonsensical babble. None of you seem to understand what you are talking about when it comes to dealing with screenshots and raster images, (a.k.a. bitmapped images) as opposed to vector or llne art.

		First of all, display devices, whether printers or monitors, have an upper limit on their ability to resolve (print or display) image detail, which by the way is what "resolution" is a measure of...meaningful detail. The best my aging but faithful laser printer can do is 600 dpi, while my uppity LCD monitor can display up to 100 dpi, with its1600 x 1200 native resolution on an LCD panel that is exactly 16" wide x 12" tall."  You cannot see nor capture anything and create a screenshot image with higher resolution than the display device. You cannot print anything with higher resolution than the printer can resolve. If you feed a high resolution image to a medium resolution printer, it will interpolate (resample) the image down to medium resolution quality. It has to, as it cannot put all of that information on paper. If you take an very high resolution (total pixel count) image of size 4000 x 3000 pixels (12 megapixels) and display the full image it on a monitor like
mine, you will
		not see all of detail in the image and hence you will not be able to capture all of the detail in a screenshot.

		Most of you seem to appreciate this, but some of you think you can improve resolution by artificial means. No, you cannot.

		A true measure of the resolution of an image is the original size of the image in total pixels, assuming it is true to begin with. That is, assuming a perfect digital camera with a perfect lens and the ability to produce a "raw" bitmap (rather than a compressed JPEG file), that 12 megapixel CCD image sensor will produce a significant improvement in the resulting image over a 2 megapixel CCD sensor. 
		That image quality is NOT described by either ppi or dpi. It is a function of the number of pixels in the X direction and the number of pixels in the Y direction.

		Now the plot thickens when I return to the subject of screenshots, because if I run my graphics card at 1600 x 1200, the type, icons and dialog boxes are uncomfortably small for me to read on the monitor, so I set the graphics card to display its images at 1280 x 960 dpi. 
		At this point, the maximum image size that can be displayed without loss of resolution is now 80 ppi. That's 1280 divided by 16. 
		[Unfortunately, since the graphics card's resolution doesn't match the native resolution of the LCD panel, the on-screen picture is not as crisp as it could be. This is a result of "aliasing" artifacts, but that's a topic for a different thread.]

		Note that in the above paragraph, I switched from dpi for display devices to ppi when describing image size. This is a meature of the physical size of a digital image (as printed or displayed) and should be described in ppi. The ability of a device to display or print an image should be described in dpi, or alternatively, lpi for lines per inch, or pixel spacing, as in 0.25mm. There is a tendency to intermix this terminology and hence confuse the issues you are discussing.

		Now that I have set my graphics card to 1280 x 960 for this monitor, the maximum resolution of any image I capture from the screen is 80 ppi, regardless of whether I capture a whole screen or just a region of it. If I set the "resolution" of the screen capture program (Snag-It or HyperSnap) to 80 ppi, then the resulting image will be the same physical size as it appeared on the screen, 100%. If I set the capture "resolution" to 160 ppi, then the image will be half the physical size as it appeared on the screen, BUT IT WILL HAVE EXACTLY THE SAME NUMBER OF PIXELS. The resolution has not be improved, as no more detail has been added.

		Upsampling and/or downsampling using any kind of pixel resampling (a.k.a. interpolation), whether bicubic or otherwise, ALWAYS removes detail from the image. In either case, new pixels are created that are some kind of average of the original ones. They're guesses at what shoud be there at that point in the image, and not real information that wasn't there before. No new detail nor image improvement can be added by interpolation.

		Now, however, you can re-scale an image in programs like Photoshop by keeping the same number of pixels (do not interpolate) and altering the size of the image in the X and Y directions equally. For example, if I took the 160 ppi screenshot described in the previous paragraph and re-scaled it in Photoshop without  resampling the image, and if I prescribed a new size of 80 ppi, the resulting image would grow back to 100% in size and have still have exactly the same number of pixels as before. The resolving power of the image has not changed, and no more detail has been provided. This is a correct way to get an image to the size you want it in your document. Another way is to import it as is and resize it in Frame using the image's corner anchor points while holding the Shift key down.

		Don't mislead yourselves and others by thinking that the more "resolution" in your screenshot capture application you use gives you better results, and don't mislead yourselves by thinking you can add more resolution by upsampling (or rescaling, for that matter) to a different ppi or by adding more artificial pixels.

		Now, on another topic, there seems to be a rule of thumb that "most SVGA screens are 96dpi." Someone came up with the statement that a 20" screen with a 1280 x 1024 display is, of course, 96 dpi. That's utter nonsense. Given that screen size is measured on the diagonal, and assuming the old standard 4:3 aspect ratio, a 20" screen is 16" 
		wide and 12" tall...rather like my Samsung LCDs. With 1280 pixels in the X (horizontal) direction, the screen resolution is 80 dpi, not 96 dpi. Any way you manipulate the numbers, 96 dpi is not a result. By the way, here I assumed a 4:3 aspect ratio, which is the ratio of width to height. If I ran my graphics card at 1280 x 1024, circles would be egg-shaped, since that resolution calls for a screen with a
		5:4 aspect ratio. Of course, wide screens have a different aspect ratio, but the principles are exactly the same.

		I have no idea what David meant by this statement:  "Again, referring to my last post, monitor resolution only counts if capturing an entire screen." Monitor size DOES count if you're trying to calculate the resolving power of your monitor in dpi and hence the maximum resolution attainable in a screenshot. It's the horizontal resolution of your graphics card setting divided by the width of the display area in inches or centimeters, or in the example given,
		1280/16 = 80 dpi.

		End of rant ...

		Flame away...but be sure you know what you are talking about and quit misleading others if you don't understand this.

		Dennis Brunnenmeyer
		***************************************************************************************

		At 09:09 AM 2/5/2008, David Creamer wrote:
		> > How can SnagIt capture an image at a higher resolution than what the 
		> > screen is set to?  A 20" screen at 1280 x 1024, for example, is 96
		> DPI.  How do you
		> > get 200 DPI out of that?
		>
		>Screen size (20") is meaningless, only the monitor resolution counts.
		>Again, referring to my last post, monitor resolution only counts if 
		>capturing an entire screen.

		Dennis Brunnenmeyer
		Director of Engineering
		CEDAR RIDGE SYSTEMS
		15019 Rattlesnake Road
		Grass Valley, CA 95945-8710
		Office: (530) 477-9015
		Fax:  (530) 477-9085
		Mobile: (530) 320-9025
		eMail:  dennisb /at/ chronometrics /dot/ com _______________________________________________

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	Dennis Brunnenmeyer
	Director of Engineering
	CEDAR RIDGE SYSTEMS
	15019 Rattlesnake Road
	Grass Valley, CA 95945-8710
	Office: (530) 477-9015
	Fax:  (530) 477-9085
	Mobile: (530) 320-9025
	eMail:  dennisb /at/ chronometrics /dot/ com