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PPI and DPI
Digital images are made up of horizontally and vertically pixels. Photographs need a higher resolution than images for a website because images for websites do not need to be large.
PPI or pixel density is what digital cameras and scanned images produce.
- Not all file formats carry dpi information (pixel density along X and Y). For example, GIF does not but JPG does.
- To verify experimentally, use a third-party viewer that provides internal
information tab
tab ****************************************/ $files_array=array( "http://www.irfanview.com/ IrfanView", ); /*************************************** * Require ONCE ****************************************/ $filename_temp="/officeuseonly/code/Function_url_validate_array.php"; //Change to be the file to include file_exists("$docRoot$filename_temp")? require_once ("$docRoot$filename_temp"): $message="ERROR: File ($filename_temp) does not exist"; echo"$message"; Function_url_validate_array($files_array); //MAIN function ?> . Do not use the same software (Powerpoint) used to generate the file because the generating software may place proprietary information in the header, which only it can read.
DPI is output or what you print – dots on paper.
Requesting an image of 400 dpi is an incorrect way to request an image.
- An image should be ppi
- you must know the dimensions of the image. Any digital image is capable of being reproduced at 400 ppi. The outputted size will vary depending upon how many pixels the camera records, but even images taken by your cell phone camera can be output at 300 ppi – they’ll just be tiny. It would be far more helpful to photographers if editors requested images at a particular output size. Why?
The more pixels you have in an image the smoother the image will appear AT A PARTICULAR SIZE. For instance, the same scene shot with a 3 megapixel camera, and with an 8 megapixel camera, printed at a small size (say 3 x 5 inches) will look equally sharp. But that image won’t reproduce well at 11 x 14 from the 3 mp camera, but will look great from the 8 mp camera. This is called resolution.
Resolution refers to the density of pixels in an image. It is a measurement of height x width at a certain pixel density (ppi). But digital images have no real absolute size or resolution – only a certain number of pixels in each dimension. Change the PHYSICAL size of the outputted print, and the resolution changes.
Think of resolution (pixel density or PPI) as coffee. In a cup three inches across, the liquid is dense and the color dark and rich (pixels packed densely). Spilled on a table, it spreads out thinly and no longer looks good (your “low resolution” output). At points in-between, the coffee is still dense enough to look brown and rich – still a usable image, depending upon the size.
I’ve sold images taken from a 3 megapixel digital camera, and they look great, but only if printed a quarter to half page. If what the editors are saying is that they want images that will hold up across a two page spread, then they need to say so.
And where did 300 ppi come from? Who knows. People toss that number around as if it were always the ideal output setting. The fact is that in the type of printing magazines use – off-set printing – resolution is determined by the number of Lines Per Inch (LPI). PPI for offset printing should be 1.5 to 2 times the print press’s LPI. Glossy magazines are typically printed at 175 LPI, so your image of at least 263 PPI (175 x 1.5 = 263) are often usable.
Raw Images
Raw files are the files that higher end camers create of the image. RAW images are unprocessed images and are high resolution. The resolution can only be changed by converting it to another file format, such as a TIFF or JPEG file.
- JPEG compression is “lossy” but the data lost is apparently irrelevant to the final product and the human eye can’t see it.
- Opening or displaying a JPEG image does not harm the image
- Saving a JPEG repeatedly during the same editing session (without ever closing the image) will not accumulate a loss in quality.
- It is a good idea to sharpened images and to check brightness, hue and contrast in Photoshop.
Image Resolution
- DPI and Inches affect only the size of the image as it is displayed or printed, but the actual pixels is finite in a bitmapped file.
- DPI (Dots per inch): The number of 'dots' or pixels per each inch of a printed or scanned document.
- Inches: The actual size (either printed or scanned) of an image.
These three parameters have direct effect on one another. With any 2 of the parameters known a simple mathmatical formula will give you the third. Let's look at a simple example:
An image created in Photoshop at 300 x 300 (that's 300 pixels wide by 300 pixels high) with a DPI of 100 is exactly 3" x 3".
Inches = Pixels/DPI
300 / 100 = 3
If you look at the Image Size Menu in Photoshop you can see a little easier how these relate.
Notice the Resample Image check box. This determines whether you want to actually resize the image. With this box UNchecked, when you enter a new DPI, Photoop shwill automatically change the DPI to compensate and vice-versa.
DPI = Resolution – A common mistake
Many people think DPI is all that matters. They couldn't be more wrong! A person creating graphics for print often says "I need it at 300 DPI." That really doesn't tell us much. For example, if I am scanning something for that person that is 2" x 2" and I scan at 300 DPI, I will get an image that is 600 x 600 pixels. If my original was 8" x 10", I will get a result of 2400 x 3000 pixels. That is quite a difference in both resolution AND FILE SIZE. What else is missing here. Well, it doesn't really matter what the original size of the image is (in inches), what matters is what the size of the output will be. So if the person asking for 300 DPI also added that this image (when printed) will be 2" by 2", then we can do the math! We know know that they want a final resolution of 600 x 600 pixels! We can do the math when we scan based on the size of the original, or scan at a high enough resolution and resize it in Photoshop (or any graphics program).
How does this relate to PowerPoint?
Well that's where it get's a little tricky, because PowerPoint does not really give the user an option to set the DPI, although the format of the presentation File | Page Setup is done in inches. Moreover, Powerpoint actually changes (behind the scenes) the DPI it is working in based on the PowerPoint version and your Windows display setting (i.e. small fonts or large fonts). This has really nothing to do wiht what resolution you have set-up in slide show settings and therefore your images rarely are imported at the correct size.
Moreover, there are issues with the file types being imported. JPG files will sometimes have the DPI and inches in them, GIF's will ONLY have the pixel information, and PNGs will ALWAYS (when exported from Photoshop) change the DPI to 72 no matter what resolution you were working in with Photoshop.
If you are creating for an on-screen presentation only the ONLY thing that really matters is the Slide Show Resolution shown here in the Slide Show | Set Up Show Pull-down menu.
This is the resolution that you will be playing back in. In many cases, this is set to 1024 x 768. So if you create all your photoshop files at 1024 x 768 you are creating exactly what you want played back. BUT, I'm sure many have noticed that when you export an image from photoshop as a JPG, PNG, etc... and insert them into PowerPoint, they are still not sized correctly. This is where pptXTREME's comes in!
If your PowerPoint page setup is at the default of 10" x 7.5" and you are creating a show to be played back at 1024 x 768... then, once again, it is simple math. 1024 / 10 = 102.4 DPI - Ditto for the Height. So in the pptXTREME DPI setting set the DPI to 102.4.
Now the images imported using pptXTREME PSDImport or Import/Export tools, will first look at the actual pixels being imported, adjust based on your DPI setting and BINGO they are imported at the correct size.
About:
300 dpi, 72 dpi, EXIF and dpi, resolution, printing, 72dpi, 300dpi, dpi and ppi,
pixels, printerresolution, pixels per inch, dots per inch, camera and megapixels
(MP), dpi/ppi and photoshop
PPI is Pixels per Inch and is a unit of measure for the resolution of print. Unfortunately it is usually called dpi or dots per inch.
When it concerns the inking of prints, it means DOTS PER INCH. But it is used too for PIXELS PER INCH. Though in that case one should speak of PPI. But to make it even more confusing the term DPI is also used for PIXELS PER INCH. Alas. A better notation for PIXELS PER INCH would be: px/inch. Or when we calculate it into centimetres: px/cm. More: a copy of an article that earlier was on alpenglowimaging.com. 1 inch = 2.54 cm, 1 cm = 0.39 inch
The dpi-value in the EXIF is
meaningless. It is a fictitious number.
(A photo has no dpi, only pixels)
You can find the properties of
your digital photos in a photo editing program, but also in the
Windows Explorer. Do a rightclick on your file and next: Properties > Summary > Advanced.
These properties are called the EXIF-data. Or short EXIF. In that
row also a value for dpi is given, f.e. the number 72, 180, 300
etc. This is a number without any meaning, it is an invented number! A
box (field) has to be filled in, so every producer simply invents
a number. Don't get confused, it is nonsense. A
photofile in a camera or (stored at) a computer has no size in centimeters
or inches. So no ppi (or dpi). Such a file only has a subdivision,
a resolution, in pixels. From the moment you are going to print
there is the matter of size, given in inches or centimeters. Only
then you can speak of pixels per inch (ppi, regrettably
ususally called dpi).
See fifth paragraph of: www.scantips.com/no72dpib.html#6.
Resolution is a confusing conception
RESOLUTION is just like DPI a confusing term. It has several meanings. So watch out in which contexts DPI and RESOLUTION are used.
Dpi and photoshop
Dpi (actually ppi) is only important
in case of printing. When you open a picture in Photoshop a dpi-number
is mentioned. Don’t pay attention to it. It doesn’t tell you anything,
you can change it in any number you want, it doesn’t change anything
of the picture. But beware: you have to uncheck the resample-box!
Resampling means calculating a new amount of pixels. The moment
resampling is off, you can change the dpi-number, the according
printing-measure is given. It also works the other way around: change
the printing-measure, the dpi-number of the picture will be shown.
Calculate the dpi
DPI is calculated by pixels (height or width) divided by inches (heigth or width) is dpi.
Computer Monitors
Many computer monitors are set to a resolution of 1024 x 768 pixels. Images are expressed in pixels (w x h).
An image on internet or a monitorscreen is not 72 dpi
For
example: a photo sized 512 pixels wide on a 1024 pixels-wide screen,
covers half of that screen in width. It doesn’t matter how large
your monitorscreen is measured in centimeters or inches. A photo
on a screen has only a 'size' in pixels. Of
course you can try to find out with a ruler how many centimeters
or inches that very picture on that very moment measures on your
screen. But it is useless, your videosystem works with pixels only,
not with centimeters or inches. So
forget this 72 dpi.
More information: www.scantips.com/no72dpi.html
A pixel of an image takes up the space of exactly one pixel of the screen. For example: the image below is 512 x384. On a computer monitor set to a resolution of 1024 x 768 pixels, the image below should cover 1/2 of the screen.
What gave birth to the 72 dpi-myth?
The dpi (px/inch) of the PRESENTATION of an image on the screen is identical to the dpi of that screen. So on a screen of 72 dpi the presentation of that image is 72 dpi too. But the image itself is not 72 dpi. Put it more strongly: such an image hasn’t any dpi, only pixels. And as computerscreens formerly often had a resolution of 72 dpi, the misunderstanding arose that an image on a screen or on a website is always 72 dpi. But on a screen of for instance 100 dpi is an image on that moment 100 dpi too. On a screen of 96 dpi is the image 96 dpi etc. etc. But only on the moment of presentation. The image itself has no dpi, but only pixels.
Explanation: The image is reproduced 1 to 1 (pixel on pixel), that’s why it has the same dpi (ppi) as the screen on which it is shown on that particular moment.
To determine the dpi(px/inch) of a screen:
Calculate the screenresolution (width x height in pixels). Determine
the size of your screen in one direction (width or height). Now divide
the pixels (in width or height) by inches (in width or height).
Photoshop and Save for the Web (72 dpi? No)
Why does Photoshop indicate 72
dpi at Save for the Web? Simply because a box has to be filled in.
But it is a fictitious number. Other software for example mention
96 dpi or 120 dpi.
See: www.scantips.com/no72dpib.html#6
The picture on the right side
of this page was 1063 pixels wide. I wanted it to fit in the right
column, so I resampled it with Irfanview to 178 pixels wide. With
Photoshop you can do this by means of Save for the Web. (With this,
other changes are possible too, but are of no importance for this
argumentation.)
When you have saved this picture and you open it again in Photoshop,
the imagesize-box will show you 72 dpi. When you uncheck resample,
you will be able to change the dpi according to your wish, the pixelsize
remains the same, and the printsize changes. The reverse is possible
too: change the printsize, the dpi changes. But this printsize and
the dpi have no significance if you want to put this picture on
the web. It’s only the pixelsize that matters.
That this picture is not 72 dpi, is visible when you look at Windows
Explorer or Windows Viewer. The Exif (properties box) mentions here
96 dpi. So Photoshop invents 72 dpi, and Windows thinks: let’s make
it 96 dpi.
What printers have problems with, is that people get pictures from
internet to have them printed. In case of the picture on this page:
Suppose I want to print the picture of 178 pixels wide at the size
of 10 cm wide
(= 3,9 inches). Then the dpi is 45,2. This is of course far too
low. The difference with 300 is also too big for resampling (see
below the paragraphs Dpi and Printing and Numeric Example).
But my dear printers:
this picture wasn’t and never has been 72 dpi as you always maintain.
This picture has far too few pixels for a good print at the size
of 10 cm, and far too low dpi at 10 cm (45), but never has been
72 dpi.
(Addition: When I
want to print this picture of 178 x 248 pixels at the size of
6,28 by 8,25 cm (= 2,47 by 3,44 inch), then the dpi is exactly
72.)
Dpi and printing (300 dpi and printed matter)
For printing is usually 300 dpi
required. With Photoshop you can calculate if your picture conforms
to this requirement (uncheck the resampe box!). When this is not
the case (too little dpi), you put the dpi at 300, check the resample
box, and your picture is ready to be printed. However pay attention:
when your picture is too far under 300 dpi, you might try to resample
it to 300, but what you get then is a inferior print. Too much difference
is not allowed. So consult with your printer. It is also better
to resample a picture that is far higher than 300 dpi. This has
advantages for the printer, moreover you won’t be able to see the
difference with the naked eye when printed.
300 dpi? No! Pixels, thats's what it's all about.
An example:
A 4 MP camera produces (ratio 3:2) photos of about (rounded) 2300
x 1500 pixels.
When made with a Nikon camera, you read: 2300 x 1500 pixels, 300 dpi.
When made with a Canon camera, you read 72 dpi instead.
(With the newest Canon cameras it’s usually 180 dpi.)
These photos are to be sent to the printshop, and both are to
be printed in the same size.
The Nikon photo will be accepted because it is 300 dpi, which
is according to the demands of the printshop. The Canon photo
will be returned because of its resolution, which is too low,
and its too bad quality to print. According to the prinshop,
this photo doesn’t meet the requirements because the dpi is
far too low to get a good print.
MADNESS! THIS IS NO EXCEPTION, THIS IS THE RULE.
This is because one doesn’t understand what dpi/ppi really is. That
photo by Canon has exactly the same quality as the one by Nikon
(perhaps it is even better, f.e. a sharper, better exposure,
less noise) and can be printed in the same size as that one
by Nikon. Because the Canon photo has the same amount of pixels.
Only Canon chose at random the number 72 to be put in the dpi-box,
while Nikon chose number 300 in the same way. Kodak took 230.
Another manufacturer chose 180, etc.
But such a number has no meaning whatsoever. You can rub or
cross this number out and replace it by another number (as
it is a digital data, you can of course not rub or cross it
out really, you must do this by means of Photoshop).
And when you change in case of the Canon photo the number
72 into 300 in Photoshop (or Irfanview) (uncheck the resample-box!),
you save this photo and send it to the printer, he/she will
say: 300 dpi, perfect photo.
This while the quality of the photo hasnt’ been changed
at all! Same exposure, same number of pixels, nothing
has changed. Only the number of 72 has been changed into
300. I think the printer (or his preparer) could have
done this quicker himself.
Another example:
A 4 MP camera, ratio 3:2, produces a photo of about 2300
x 1500 px.
A 5 MP, ratio 3:2, produces a photo of 2600 x 1700 px.
Suppose the first photo comes from a Nikon camera, than
you read: 2300 x 1500 px, 300 dpi.
The second one is from a Canon camera, here the info mentions:
2600 x 1700 px, 72 dpi.
Both must be printed at the same size.
The first photo will be accepted by the printer, the second
one will be returned because of its too low resolution.
This is absurd, because it is just the reverse: the second
photo has a higher resolution.
The resolution of a (not yet printed) photo is the pixelsize
( see third paragraph on this page).
NEXT PARAGRAPH: WHAT CAN GO WRONG!
See also:
What Print Shops Really Want: www.rideau-info.com/photos/printshop.html
Ken Watson applies to people from the printing-shops,
and says STOP DOING THIS, ask fot the number of pixels
you need, and not for the dpi.
Changing the DPI: www.rideau-info.com/photos/changedpi.html
Ken Watson tells us here: If a printer still
asks for a photo with so much dpi instead for a
photo with so many pixels, dont’ try to explain
the way it works, give them what they ask for, change
the dpi of the photo in whatever number they want,
300 or it doesn’t matter what, as long as you don’t
resample. The dpi-number is
meaningless, and a change of that
number doesn’t alter your photo.
Deliverspecification for printed matter 300 dpi. What can go wrong.
Photos intended for printing must be delivered in 300 dpi (deliverspecification). It happens that in practice this is required too even when the printsize isn’t known yet. Actually ridiculous (see preceding paragraphs) but it happens regularly. This is no problem when the customer knows that it is possible to uncheck resampling in Photoshop (or Irfanview). If the customer doesn’t know this, things can go pretty wrong.
For example:
1. Pictures made with my 4 MP Kodak Camera, are loaded in Photoshop
as follows:
2304 x 1536 px, 230 dpi, and (of course because of that 230 dpi)
10,017 x 6,678 inch.
2. I change this to 300 dpi and I don’t know that I must uncheck
resampling, so I get:
3005 x 2003 px, 300 dpi, printingsize stays 10,017 x 6,678 inch.
3. Suppose the printingsize must be 8 inches wide (of course the
300 dpi must not be changed), then you get:
2400 x 1600 px, 300 dpi, 8 x 5,333 inch.
This means that at first there has been a resampling upwards at
3005 x 2003 pixels. After this resampling downwards to 2400 x 1600
pixels. But resampling was quite unnecessary. Quite a pity to to
spoil your beautiful photos in this way!
So: When the printsize is not yet known and the printer requires
that you must deliver your photos in 300 dpi, uncheck the resample-box
in Photoshop (or Irfanview)! In that case nothing can go wrong.
Read also: Ken Watson - The Horrible DPI Mistake, on
his page The
Myth of DPI
Wrong: Deliver photos at 300 Dpi. (This is what you read at
the sites of the greater part of the printshops, above you can read
that because of this you will get bad prints.)
Printers should say: Photos must be delivered with enough pixels,
so that they can be printed at minimally 300 dpi (actually ppi, px/inch).
Art Prints, pay attention!
When you have really beautiful photo’s which you want to have perfectly printed, then it’s worth the trouble to join hands with a printer who specializes in that kind of printing (called art print). Then it’s possible to deviate from the strict requirement of 300 dpi. (This seems contradictory to the preceding paragraph, but this is caused by the finer grid which is used for art prints. That’s why it makes sense to work with a higher dpi.) Of course this procedure is more expensive. Inquire and consult to avoid disappointment.Numeric example
I own a 4 MP camera.
When I’m taking pictures, ratio 4:3, the picture will be 2304 x 1728
pixels, and W x H in pixels is then 3.981.312 = (rounded off upwards)
4 MP.
In ratio 3:2 they will be 2304 x 1536 = 3.538.944 = (rounded off)
3,5 MP.
I mostly take pictures in ratio
3:2. Suppose I want a print of size 15
x 10 inch, then the dpi
will be: 2304/15 = 153,6 (or when I calculate it with the height:
1536/10 = 153,6).
This is far below 300 dpi. I could resample, but the difference
between 153 and 300 is too much, the picture will be of a very bad
quality.
When I start from 300 dpi, I can make the following calculation:
2304/300= 7,68 en 1536/300= 5,12. So
a picture of (rounded off) 8 x 5 inch is the maximun printingsize
for the photos made with my camera, starting with a dpi of 300.
In case of calculating this for your own photos: when a little
below 300 dpi for a certain printing-size, you can resample
with Photoshop. When far above 300 dpi, you have to resample
downwards.
Schematically:
· divide pixels by inches, is the outcome > or
exactly 300, you get a good print
· divide pixels by inches, is the
outcome < 300, you have to add pixels (resamplen)
· divide pixels by 300, and
you’ll get the maximum printsize
in inches
· divide pixels by centimeters,
is the outcome > or exactly 118, you get a good print
· divide pixels by centimeters,
is the outcome < 118, you have to add pixels
· divide pixels by 118, and
you’ll get the maximum printsize in centimeters
But once more: the dpi
must not be too low,
for in that case resampling has no use any more. You’ll
get a very bad picture (where is the limit, I don’t know exactly,
so consult your printer).
And now for something else:
1. What you read above
is the official story, the thing you have to reckon with as printers
start from these. But as a matter of fact it is no more than a directive. At
the beginning the norm was 240,
but a broader margin was wanted, after rounding off upwards the
norm was fixed
at 300 dpi.
Yet there are more factors which determine a good print, for example
the quality of your cameralens. You can read more about this at Ken
Rockwell’s site: www.kenrockwell.com/tech/mpmyth.htm
2. Ken Watson thinks nowadays
200 dpi is sufficient for printing. On his site www.rideau-info.com/photos you’ll
find among others the following articles: What Print Shops Really
Want, and Changing
the DPI.
Dots per inch (inkdots)
DPI as DOTS PER INCH (as distinct
from PIXELS PER INCH), are the small inkdots (per inch) that come
on the paper during the printing-procedure. The DPI (dots/inch)
must be larger than the DPI/PPI (pixels/inch), otherwise the result
will be a bad print. An example: A print has 300 pixels per inch
and 1200 dots per inch. In this case each pixel has the average
of 4 (ink)dots. Back to second
paragraph.
Printing at home and printerresolution
Dpi (dots per inch)
At home you are usually printing with an inkjetprinter. When printing
a colour print it puts on each pixel several dots (inkdrops) (see
previous paragraph). Some printers have a higher dpi than other
ones, and you tend to think: the higher the better. This needn’t
always be true. Other technical aspects of a printer are no less
determining for the quality of the print. For example the way
colours are mixed, the space between and the size of the inkdrops,
and much more. Instead of relying on the dpi better read the reviews
at the websites which are known as reliable.
Dpi (pixels per inch)
When printing at home there is in general no need to adjust the dpi
(pixels per inch) (as described in the paragraph Dpi and Printed Matter).
Although it is sensible to make an estimation at what size your picture
approximately (maximal) can be printed. A homeprinter usually produces
still good prints at 200 dpi (pixels per inch). You can make a proof
in order to see if the result is satisfactory. If not, make a smaller
print, or raise the dpi (ppi) with, for example, Photoshop or Irfanview.
See for explanation elsewhere on this page.
Numeric example:
200 dpi (ppi) = 200 pixels
per inch = about 80 pixels per cm. So a print of 15 by 10 cm has to
be 1200 by 800 pixels minimally. If not, resample as described elsewhere
on this page.
A useful trick to be able to know quickly how large a picture roughly
can be printed in centimetres is: divide pixels by 100.
Explanation: 100 pixels per cm = 254 pixels per inch = 254 dpi
(ppi).
Dpi and scanning
An example: you want to print a photo sized 4 by 5 inch the same size. Than you have to scan it at 300 dpi. If you wish to print it at 8 by 10, you’ll have to scan at 600 dpi, the print will be 300 dpi. The question is, can your device manage it, it makes great demands on the memory. But essentially this is the way it has to be done. More info: www.scantips.com
Camera and megapixels (MP)
The MP of a compactcamera is usually based on the production of photo’s of 4:3.
(Also see paragraph Numeric Example as mentioned above.) My camera is specifically called a 4 MP camera. A photo of 4:3 (adjusted at best quality or highest resolution) has 2304 x 1728 pixels = (rounded off) 4.000.000 pixels = 4 MP.
(The camera can also be adjusted at a lower resolution, in that case you get a picture with fewer pixels in both width and height.)
When I set the camera at 3:2, in the highest resolution, the picture will have 2304 x 1536 pixels = (rounded off) 3.500.000 = 3,5 MP. This picture is of the same quality, the same resolution as the picture of 4:3! The number of pixels changes, caused by ratio and not by quality! Width remains the same (2304 pixels), but height changes from 1728 into 1536, so in all there are fewer pixels.
So if you know the MP, you can calculate the number of pixels. 4x x 3x = MP. So 12
x square is MP.
When for instance you own a compactcamera of 5 MP, then the procedure
is as follows: 12 x square
= 5.000.000. Calcultate the x and
you will see that the picture will be (approximately) 2582 x 1936
pixels.
(Explanation: divide 5.000.000 by 12, extract the root, multiply
this number with respectively 4 and 3, and you’ve got W x H in
pixels.)
So by means of the MP of a camera you are able to calculate the
printsize of your pictures. First calculate the number of pixels
with the formula 12 x square.
Then divide by 118, and you have the maximum printsize in centimeters
(for inches: divide by 300). (See scheme in the paragraph Numeric
Example.)
With a reflexcamera the MP-indication usually
gives the number of pixels of a photo ratio 3:2. So f.e. a 6
MP camera, adjusted at the highest resolution, produces photo’s
of approximately 3000 x 2000 pixels. (Same calculation as with
compactcamera, but now 6 x square
= 6.000.000)
Advantages and disadvantages of a camera with a high MP
Is a camera with a high MP better
than a camera with a low MP?
No, the quality of the picture has to do with other factors, not with
the number of pixels.
The advantage of a camera with a high MP
The higher the MP, the more pixels a photo has, the larger
this photo can be printed. This especially is important when you
frequently make crops. The number of pixels decreases, through which
the maximum printingsize gets smaller (compared with the original
photo).
(But for very large prints the MP can even be lower, as these photos
are viewed at a very great distance.)
The disadvantage of a camera with a high MP:
The files are getting bigger (in KB or MB). So your memory
card will earlier be full, storage at the computer requires much
room, sending by mail often is not possible in the original resolution.
(It is often possible to set the camera in a lower resolution, a lower
MP. Don’t mix this up with the JPEG-compression, this certainly has
to do with the quality of the picture!)
You can work it out for yourself now with the information as given in the previous paragraph: a 6 MP camera will be amply sufficient for most people. And as with printing at the customary size a 4 MP or 5 MP camera meets too with the demands.
Link: The Megapixel Myth - www.kenrockwell.com/tech/mpmyth.htm
What happened before
Just like many other
people I got confused when I wanted to have pictures printed and
I was told that I had to deliver them at 300 dpi. The pictures I
had made with my Kodak-camera were 230 dpi, at least this was mentioned
in the Exif-data. Asking questions about the meaning of that number
in photostores resulted in rambling stories. Making inquiries at
Kodak Nederland gave the following result: one didn’t believe that
a dpi-number was mentioned in the Exif, because a stored picture
has no dpi, I was told. When they found out that really 230 dpi
was mentioned in the Exif of the Kodak-pictures, they found this
odd. I searched on internet for the meaning of dpi. With the information
I gathered I couldn’t explain the dpi of my pictures. And that may
be right, for on an internet-forum I read the only plausible explanation:
it is a fictitious number, some number has to be filled in. I think
that this “box” is inserted in view of the printing of photos. But
as long as printing is out of the question, that fictitious number
is senseless and confusing. I take it ill of camera-manufacturers
that they omit to supply information about this. The same applies
to books about photography. Hardly ever you”ll find this explanation
there. That’s why I have put this information on internet. .
Dpi in the education for the graphical sector
From various sides I learn that in the schooling for the graphical sector the misunderstandings about dpi, as described above, are still taught (in The Netherlands, but also in most other countries). It turns out to be very difficult to convince the graduates form these educational institutions (who find themselves in the printing trade) that they are mistaken. They certainly find it hard to accept this from an outsider.
Illustrative is the reaction on a forum by a former pupil of a graphical school: OK, so I understand that at the graphical school everything has been explained incorrectly. This seems rather strange to me. This can’t be wrong, I’ve got this from school. It was drillled into our heads.
This attitude I’m afraid will only change when someone inside the
trade group realizes that something is amiss on this point in the
printing trade and starts to act to bring about a change in the schooling.
Maybe this will happen only when the sector realizes that it profits
by it: less frustration in the contacts with clients, less mistakes,
less loss of time. We will see.
See also: www.emdpi.com. The
author of this site states the sort of mistakes he came across in
a textbook on graphics. A “thumbs down” indicates that the given
information is wrong.
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