Resolution?

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Posted By
E_Nolan_Brown
Sep 8, 2007
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370
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6
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I have a Dell Photo AIO All In One Printer 922; includes printer, fax and scanner. According to the literature, it can print up to 4800 dpi. However, the scanner that’s built in can only scan up to 300 dpi (or I guess that should be samples per inch) which seems a little odd to me. Also, I created a 3" by 5.33" Photoshop file at 4800 ppi to test the quality of the print, but it is a huge 230 MB file. Not sure I want my files taking up this much space.

The 4800 dpi just sounds wrong to me. Does 4800 dpi sound normal or are they using the term out of context; i.e. really meaning that it will print a total of 4800 dots across the entire page?

Also, please let me know if you recommend any good books, tutorials, etc on the topic of image, scan, print and display resolution that could help me understand all of this.

I’m a novice regarding this topic, so it is very confusing to me at this point.

Thanks,

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C
chrisjbirchall
Sep 8, 2007
DPI and PPI are two totally different things.

DPI (DOTS per inch) relates to the number of dots a printer is capable of spraying per inch of media (paper). 1440 DPI is considered as High quality in ink jet terms 2880 DPI as Very High or Photo Quality.

PPI relates to the number of PIXELS per inch in an image file.

Although 300 ppi has become the norm for high quality printing, most ink jet printers will produce exceptional quality from images with a resolution of 240 or even 180 ppi.

The printer driver converts the pixel information PPI into signals which are fed to the (seven or more) jets, translating them into dots DPI.

Want to learn more? Spend half an hour or so at <http://www.scantips.com/>
EN
E_Nolan_Brown
Sep 8, 2007
Thanks for the info.

So, ppi and dpi don’t correlate on a 1:1 ratio? i.e. 100 horizontial pixels = 100 horizontal dots.

This is more complicated than I thought.
J
Jim
Sep 8, 2007
wrote in message
Thanks for the info.

So, ppi and dpi don’t correlate on a 1:1 ratio? i.e. 100 horizontial pixels = 100 horizontal dots.

This is more complicated than I thought.
On most printers, a given dot can only be one color. Hence, it takes at least a 3×3 matrix of dots to form a pixel.
Dots aren’t pixels.
Jim
DP
Daryl_Pritchard
Sep 9, 2007
Nolan,

No, ppi:dpi is not 1:1 and I suggest you not really even try to compare the two. Any time you see DPI referenced, treat it as meaning PPI if the device of interests is anything other than a printer. Unfortunately, many manufacturers will still use the DPI parlance when, indeed, they really mean either pixels or samples per inch. Meanwhile, "dots" at least makes some degree of sense if you think in how a printer creates an image by laying down "dots" of ink. The smaller the dot and tighter that multiple dots can be sprayed onto print media, the higher the apparent image quality.

But, if you talking about scanners, digital sensor resolution, display devices, or computed file sizes, all of these deal strictly with pixel data. Digital sensors (in cameras) are one new area in my opinion where the waters have been muddied even more, given how they are quoted as having a resolution of X megapixels when resolution more commonly defines a certain number of something per unit of measure. Just as DPI and PPI are used in ways that confuse an individual, the same is true of "resolution" itself.

And actually, at least in my opinion, it is not complicated at all. Just think pixels and PPI, and forget you ever heard the term DPI. True enough, DPI is important with printers, but most photo-quality printers by definition have the DPI you need, so I think it can be ignored for the most part.

Regards,

Daryl
KV
Klaas Visser
Sep 9, 2007
Daryl’s advice is excellent, and I’ll offer my experience as an example.

I have an Epson 1290, which is capable of printing up to 2880 dots per inch. However, within Photoshop, I usually work in 240 pixels per inch for output to the printer.

When going to print, I select the media type I’m using, and the printer driver selects the dots per inch it wants to use for that particular type of paper. For example, printing to Premium Glossy Photo paper, the driver will set itself to 1440 dpi, and printing to Colorlife Photo paper (a semi-gloss satin finish), the driver sets itself to 2880 dpi. It does this to allow for coverage and drying, absorption into the paper, etc.

So I don’t worry about the printer’s DPI, and just focus on the image’s output setting in PPI, having established, through a little bit of trial and error, that 240 PPI provides for excellent output on my printer.
T
Talker
Sep 9, 2007
On Sat, 8 Sep 2007 14:21:37 -0700,
wrote:

I have a Dell Photo AIO All In One Printer 922; includes printer, fax and scanner. According to the literature, it can print up to 4800 dpi. However, the scanner that’s built in can only scan up to 300 dpi (or I guess that should be samples per inch) which seems a little odd to me. Also, I created a 3" by 5.33" Photoshop file at 4800 ppi to test the quality of the print, but it is a huge 230 MB file. Not sure I want my files taking up this much space.

The 4800 dpi just sounds wrong to me. Does 4800 dpi sound normal or are they using the term out of context; i.e. really meaning that it will print a total of 4800 dots across the entire page?

Also, please let me know if you recommend any good books, tutorials, etc on the topic of image, scan, print and display resolution that could help me understand all of this.

I’m a novice regarding this topic, so it is very confusing to me at this point.
Thanks,

Hi Nolan! To make it simple, I would suggest that whenever you want to print an image, make sure that the image has a resolution of 300 dpi (or ppi which are interchangeable). You can get away with 240 dpi, but I prefer 300 dpi. Keep in mind that this is the resolution of the image itself.
Now when you print the image, the printer will have different dpi settings also, but most of them will usually give you the option of printing "Average….Good……Better….Best" or something like that. If the printing software allows you to enter ina specific number, like say 1200 dpi or 1440 dpi, then enter in the highest dpi that gives you the desired quality. You don’t necessarily have to enter in the highest setting that the printer has, just the setting that gives you the best results.
My printer has a 1200 dpi setting that I’ve used twice, and it uses a lot more ink than my usual 600 dpi setting, yet the 600 dpi setting results in excellent photo quality prints. I used the 1200 dpi setting on two small prints that seemed to have a trace of banding in them. This was the only time this occurred, and hasn’t happened since, so I never need to use the 1200 dpi setting.
When you scan a picture, then the dpi means something different. If you scan a picture that’s 2 inches high by 3 inches wide, and you want to print it out at 2 inches by 3 inches, then you should scan it at 300 dpi, since that’s what the printer needs to print it out as….2 x 3 at 300 dpi.
If you are going to scan this 2 x 3 picture, but you want to enlarge it to 4 x 6 inches when you print it, then you should scan it at 600 dpi. If you scan a 2 x 3 inch picture at 600 dpi, then resize it to 4 x 6 inches, then the picture will resize to 4 x 6 inches at 300 dpi. If you do this in PhotoShop, you will need to go to "Image"…."Image Size", and check the "Constrain Proportions" box, and uncheck the "Resample" box, then enter in the new size of 4 x 6 inches. When you do this, you will see that the "resolution" box will change from 600 pixels/inch to 300 pixels/inch, but that the "Pixel Dimensions" sizes at the top of the window will remain the same. What happens is that the picture had 600 pixels per inch and it covered a 2 inch by 3 inch area. When it’s resized, it now has 300 pixels per inch but it’s now covering a 4 inch by 6 inch area. It still has the same number of pixels, but they are spread out over a larger area, so you end up with less pixels per inch. Since you needed an image that was 300 dpi to send to the printer, the resulting 4 x 6 picture is now 300 dpi.

Talker

How to Master Sharpening in Photoshop

Give your photos a professional finish with sharpening in Photoshop. Learn to enhance details, create contrast, and prepare your images for print, web, and social media.

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