questions regarding resolution and pixels and size

PenthouseFan · February 19th, 2010, 08:21 PM

Can I ask some questions regarding resolution and pixels and size that I don't understand ?

(1) I start out scanning a page from a magazine that is rich in color. Let's say it has 1 picture that takes up 80% of the page and a little insert photo that takes up maybe 10%. The rest is words.

(2) These scans are done using a pretty basic Canon printer/scanner. After I scan the page, they on average measure about 5000 x 6000 pixels (30 MM pixels). I am scanning at 600 dpi so I presume that the original pixel resolution would go down if I cut it to 300 dpi or 150 dpi -- is that true ?

(3) OK, I have my page scan and then I crop the 2 pictures. The bigger one (maybe 6x8") is maybe 3000 x 2000 and the smaller one (maybe 2x2") is 1500 x 1000 pixels.

(4) OK...I save them to Picasa and they each measure many megapixels....even the little one I see is 16 mbytes.

(5) Then...I export and resize....I use 1600 pixels and MAXIMUM on Picasa...and the pixel dimensions ARE THE SAME for the smaller picture but the size of the file is now just over 1 mbyte. WHAT HAPPENED ? How can the pixel dimensions be the same and now the file size is 1/15th what it was before ? I don't see any diminishment of quality in the picture when it fills my 19" monitor so what advantage did the 16 mbyte file/picture have over the 1 mbyte file/picture if it isn't any sharper/clearer at any size ?

Am I not loosing any resolution in these scans and crops and resizes because I originally scanned at a high-quality (600 dpi) setting and my scanner is giving me 30 MM pixels to work with ?

I have other photos that are like 320X240 and when I try and make those big on my monitor, you definitely see it get pixel-ated and less clear.

I guess I'm trying to ask when does more pixels result in 'overkill' and just a bigger file type, how can you make pictures maximum sharp without being so big that you can't see them on your monitor (or is there an inherent tradeoff there), and what should or should not be done with the original printer scan and the subsequent Picasa re-sizing that makes the picture good or bad ?

Any definite 'do's' or 'donts' ???

AdamApple · June 18th, 2010, 11:09 PM

As a general rule (and I'm a digital archivist of sorts so know what I'm talking about here) it pays not to conflate the two output choices when transcribing.

When scanning solely for the screen then a resolution higher than 150dpi serves little purpose unless you are magnifying a section of a page. Giant high-res images allow scrutiny but don't work well in slide shows and eat up space.

When scanning for repro/print your minimum resolution is 300dpi though you should scan higher for enlargements.

A scan for print use can be down resolved for the screen but rarely the other way.

Don't confuse resolution with size. Actual image size may be constant in terms of pixels but its display or print wil vary depending upon the specified resolution. Your screen resolves at somewhere between 72 and 90dpi (dep. on type) so a 3000pixel square image will have to be shrunk to display full screen. However, your printer will optimise at 300dpi producing a 10x10" image - much smaller than the screen equivalent but the screen creates an illusion of definition.

"Don't" No 1: DON'T use Picasa or any other widgets/gadgets/plug-ins.
"Don't" No 2: DON'T rely upon the scanner engine or bundled software other than to optimise what the scanner "sees".

"Do" No 1: DO read up on histograms and descreening.
"Do" No 2: DO use an accurate image editor such as the Gimp.

**Dekoda** · July 18th, 2010, 08:14 AM

When you scan a picture from a magazine, you need to decide what size you want that final image to be. Are you going to post the scanned image on the internet? Is that the only thing you want to scan the image for?

If you are scanning this picture so that you can post it on the internet, then you need to decide on the final output size. When I was scanning, I used the output size of 1024 pixels by 768 pixels. I used that size because back then, that was considered large. Most monitors could only display either 800 X 600 or 1024 X 768. I elected to use the 1024 x 768, since that was the up and coming size.

Okay, once you have determined what size you want the final picture to be, you need to figure out what size you need to scan the picture at so that you will end up with the size you want. If the picture is a full page picture, then scanning it at 75 dpi will usually work. Of course, that's if your end result will be the 1024 X 768 size.

The idea is to not scan the picture at a huge size....like 600 dpi. If you scan at 600 dpi, then you will need to resize the picture so that it will fit on your monitor. Downsizing a scan from 600 dpi to whatever size you want, will cause the scan to lose a lot of quality. It will look soft.

I see a lot of people scan magazine pictures at high resolutions. There is no need to do that. You are just creating a huge file that serves no purpose. I don't think I ever scanned any picture at more than 300 dpi. Of course, if you have a really small picture and you want to end up with something like a 1600 X 1200 picture, you might need to scan at more than 300 dpi, it depends on what size you want to end up with.

The scanning software that I use for my Canon scanner, allows me to type in any dpi I want. What I do is to do a pre-scan, then, when I see the picture in the scanning software, I outline the picture, and the scanning software tells me what size the output will be. By adjusting the dpi, I can then get an output that is the size I want the final picture to be.(1024 x 768).

If the picture in the magazine is the size of a matchbook and you want the final picture to be 1600 X 1200, then you need to determine the correct dpi to scan the picture at to result in a 1600 X 1200 final size. My scanning software does that. All I have to do is type in a dpi size, and it shows me what the final output size will be. I would think that most of today's scanners come with scanning software that will do that. I usually increase the dpi to give me a resulting scan that is slightly larger than what I want the final picture to be. That allows for cropping and slightly reducing the size of the picture to give me the desired size I want.(that's the 1024 X 768).

Let me say that this is my technique. That doesn't mean that it's the only technique out there, it's just the technique that I use. Others may have their own technique that works for them.

February 19th, 2010, 08:21 PM	#1
PenthouseFan Senior Member Join Date: Jan 2010 Posts: 201 Thanks: 110 Thanked 3,166 Times in 185 Posts	questions regarding resolution and pixels and size Can I ask some questions regarding resolution and pixels and size that I don't understand ? (1) I start out scanning a page from a magazine that is rich in color. Let's say it has 1 picture that takes up 80% of the page and a little insert photo that takes up maybe 10%. The rest is words. (2) These scans are done using a pretty basic Canon printer/scanner. After I scan the page, they on average measure about 5000 x 6000 pixels (30 MM pixels). I am scanning at 600 dpi so I presume that the original pixel resolution would go down if I cut it to 300 dpi or 150 dpi -- is that true ? (3) OK, I have my page scan and then I crop the 2 pictures. The bigger one (maybe 6x8") is maybe 3000 x 2000 and the smaller one (maybe 2x2") is 1500 x 1000 pixels. (4) OK...I save them to Picasa and they each measure many megapixels....even the little one I see is 16 mbytes. (5) Then...I export and resize....I use 1600 pixels and MAXIMUM on Picasa...and the pixel dimensions ARE THE SAME for the smaller picture but the size of the file is now just over 1 mbyte. WHAT HAPPENED ? How can the pixel dimensions be the same and now the file size is 1/15th what it was before ? I don't see any diminishment of quality in the picture when it fills my 19" monitor so what advantage did the 16 mbyte file/picture have over the 1 mbyte file/picture if it isn't any sharper/clearer at any size ? Am I not loosing any resolution in these scans and crops and resizes because I originally scanned at a high-quality (600 dpi) setting and my scanner is giving me 30 MM pixels to work with ? I have other photos that are like 320X240 and when I try and make those big on my monitor, you definitely see it get pixel-ated and less clear. I guess I'm trying to ask when does more pixels result in 'overkill' and just a bigger file type, how can you make pictures maximum sharp without being so big that you can't see them on your monitor (or is there an inherent tradeoff there), and what should or should not be done with the original printer scan and the subsequent Picasa re-sizing that makes the picture good or bad ? Any definite 'do's' or 'donts' ???

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June 18th, 2010, 11:09 PM	#2
AdamApple Member Join Date: Nov 2009 Posts: 76 Thanks: 563 Thanked 3,330 Times in 129 Posts	As a general rule (and I'm a digital archivist of sorts so know what I'm talking about here) it pays not to conflate the two output choices when transcribing. When scanning solely for the screen then a resolution higher than 150dpi serves little purpose unless you are magnifying a section of a page. Giant high-res images allow scrutiny but don't work well in slide shows and eat up space. When scanning for repro/print your minimum resolution is 300dpi though you should scan higher for enlargements. A scan for print use can be down resolved for the screen but rarely the other way. Don't confuse resolution with size. Actual image size may be constant in terms of pixels but its display or print wil vary depending upon the specified resolution. Your screen resolves at somewhere between 72 and 90dpi (dep. on type) so a 3000pixel square image will have to be shrunk to display full screen. However, your printer will optimise at 300dpi producing a 10x10" image - much smaller than the screen equivalent but the screen creates an illusion of definition. "Don't" No 1: DON'T use Picasa or any other widgets/gadgets/plug-ins. "Don't" No 2: DON'T rely upon the scanner engine or bundled software other than to optimise what the scanner "sees". "Do" No 1: DO read up on histograms and descreening. "Do" No 2: DO use an accurate image editor such as the Gimp.

July 18th, 2010, 08:14 AM	#3
Dekoda Vintage Member Join Date: Jul 2010 Posts: 823 Thanks: 20 Thanked 24,261 Times in 822 Posts	When you scan a picture from a magazine, you need to decide what size you want that final image to be. Are you going to post the scanned image on the internet? Is that the only thing you want to scan the image for? If you are scanning this picture so that you can post it on the internet, then you need to decide on the final output size. When I was scanning, I used the output size of 1024 pixels by 768 pixels. I used that size because back then, that was considered large. Most monitors could only display either 800 X 600 or 1024 X 768. I elected to use the 1024 x 768, since that was the up and coming size. Okay, once you have determined what size you want the final picture to be, you need to figure out what size you need to scan the picture at so that you will end up with the size you want. If the picture is a full page picture, then scanning it at 75 dpi will usually work. Of course, that's if your end result will be the 1024 X 768 size. The idea is to not scan the picture at a huge size....like 600 dpi. If you scan at 600 dpi, then you will need to resize the picture so that it will fit on your monitor. Downsizing a scan from 600 dpi to whatever size you want, will cause the scan to lose a lot of quality. It will look soft. I see a lot of people scan magazine pictures at high resolutions. There is no need to do that. You are just creating a huge file that serves no purpose. I don't think I ever scanned any picture at more than 300 dpi. Of course, if you have a really small picture and you want to end up with something like a 1600 X 1200 picture, you might need to scan at more than 300 dpi, it depends on what size you want to end up with. The scanning software that I use for my Canon scanner, allows me to type in any dpi I want. What I do is to do a pre-scan, then, when I see the picture in the scanning software, I outline the picture, and the scanning software tells me what size the output will be. By adjusting the dpi, I can then get an output that is the size I want the final picture to be.(1024 x 768). If the picture in the magazine is the size of a matchbook and you want the final picture to be 1600 X 1200, then you need to determine the correct dpi to scan the picture at to result in a 1600 X 1200 final size. My scanning software does that. All I have to do is type in a dpi size, and it shows me what the final output size will be. I would think that most of today's scanners come with scanning software that will do that. I usually increase the dpi to give me a resulting scan that is slightly larger than what I want the final picture to be. That allows for cropping and slightly reducing the size of the picture to give me the desired size I want.(that's the 1024 X 768). Let me say that this is my technique. That doesn't mean that it's the only technique out there, it's just the technique that I use. Others may have their own technique that works for them.