Everything you wanted
to know about file size
and formats, and
a few things
Note: too many calls regarding this article - please read the article and take what you can from it, however I cannot take the time to answer additional questions by phone. I may be able to assit you by email and some services may require a fee or donation. A few too many people have called me asking for help and I simply don't have the time to help everyone. Read and enjoy. thanks. -
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is John Lacy,
a commercial photographer
based in the
metro Detroit area,
serving the entire Midwest.
high quality photography
mostly for business to business marketing.
Our principal markets are
the construction industry
and the automotive
A significant portion of our work is also divided
among the hospitality industry (hotels, resorts, casinos & restaurants)
Our specialties include
(interior & exteriors),
(interiors & exteriors,
studio & location),
shooting manufacturing facilities & equipment.
>> Environmental & Studio
for Editorial, Annual Report
glass, plastic, package goods & food.
In addition to photography
we also offer
>> Digital Retouching
>> Large Format Printing
>>Graphic Design &
Offset Printing for
brochures, catalogs and
Website Design & Hosting.
We've been in business
Well it happened again. I
got a request from a new client requesting a file as "300dpi". I replied
with a long explanation as to why this wasn't enough information for me to
fulfill the request. At the end I asked "So what size did you need that
image? And what are you needing it for?"
I got the following reply;
"I don't need the
dissertation. To use your same logic,
for me to ask for an image of
a certain size in a set resolution assumes I am aware of what file
size you use....I am not. I could be decreasing the resolution with
such a request. I am also fully aware of the compression issues
with JPG files.
Send me the file as
large as you can email it; TIFF is fine as is the RGB JPG. I can
deal with any format and the image size thank you."
So rather than
educate my client and get the information I needed I only ticked him
off by over explaining what dpi is and why "300dpi" doesn't mean
To avoid this situation in the future I would like to give everyone who may
be interested access to all of the answers about DPI, PPI, File Size and
Format so they can understand what is needed to meet their needs.
So as not to be condescending, nor explain something in infinitum that which is
already well understood by the reader I have written each explanation with a
bolded title. You can scan over these and only read those areas that
interest you, or may be relevant to your needs, skipping over those areas you
are already well acquainted with.
I get requests almost every
week for a file as "300dpi". This is an incomplete equation. I've tried
explain this using various analogies and so far none has been ideal, but I
will try again; suppose you are buying tires for your car and when the
dealer says "what size tires do you want" you say "I don't know, but I want
it in inches".
I can give you a 1"x1" photo at 300dpi. That's
probably not what you need, but when the client asks for 300dpi they have
probably been told by a publisher or printer that images must be submitted
as "300dpi" without further explanation.
The complete equation is to have the dimensions of the image and the
resolution. One without the other is useless. For example 4"x5"
or 5"x7" are commonly used sizes. If I
then make the file "300dpi" that makes an
image file that is 1200 pixels by 1500 pixels for the 4x5,
or 1500px by 2100px for the 5x7. If you
multiply the two dimensions (1200px x
1500px =1.8M) you see where "megapixels"
come from. You may be familiar with "megapixels" from its use in describing
the resolution of images produced by consumer digital cameras. While a "megapixel"
description of a file size may make more sense than "300dpi" it doesn't
account for the preferred resolution or proportion of the image, only the
So where does that leave us? As it turns out dpi is actually the wrong term
for nearly every application it's used so lets start there;
DPI stands for "Dots Per
Inch" which is fine if you are counting dots. In the vast majority of cases
we are actually counting pixels. Pixels are the square, solid colored
smallest element of an image file. When we use DPI we most likely really
mean Pixels Per Inch or PPI.
So where did DPI come in? Printers, both consumer desktop prints and big
commercial printers print "dots" of ink onto paper. The dots may be in
clusters called "Rosettes" which simulate the wide range of colors we see in
print using only 4 ink colors Cyan, Magenta, Yellow and Black (CMYK, where K
A desktop printer may use 4-8 different color inks, placing the individual dots
"Stochastically" (rather than using Rosettes) to appear as a wider "gamut"
of color. Why 300 dpi?
Before digital technology a commercial printer used a "screen" to turn a
continuous tone image into one made of dots using a "half tone" process.
This can be done with both black & white as well as color images. For color
the "screen" is rotated slightly for each color of ink to reproduce the full
color. If the screen is too fine the dots might run together on the press
and look blotchy. The fineness of the screen is called "Line Screen" and
its resolution described as Lines Per Inch (LPI). Resolution when using
this type of printing is therefore described as Line Screen. To make a continuous tone
black and white photograph reproduce properly it is standard convention that
the resolution of the photo be at least 50% higher and ideally twice as high
as the Line Screen. At the turn of the century (2000) the most typical line screen
was 150LPI. Photo images to be converted for printing a 150LPI are
recommended to be 300dpi (twice the line-screen) at its final reproduced
As it turns out now that we are in the digital age most printers don't use a
"screen" to convert printed photos. Most photos are now supplied in digital
form and as such are in Pixels. The 150 Line Screen standard is now also far
less standard with many printers producing excellent quality publications at
175, 200 even 400 Line Screen resolutions.
Okay, so to review; 300dpi is a standard derived from printers who used to
reproduce images using a 150 line screen to prepare printing plates. If you
are requested to supply an image at 300 dpi it can in fact be as low as
225ppi or as large as 350-400ppi, but remember that it needs to be at the
final size (dimensions) in which it will be reproduced.
How to make a 300dpi file;
If you open your file in Photoshop and then use the short cut Alt+Ctrl+I (or
on the menu bar Image>ImageSize) you will bring up the Image Size dialogue
for the selected open image file. At the bottom unclick "Resample Image".
With this setting you can change the size and resolution without damaging
the file. Notice that changing one setting makes the others change as well
in proportion. Setting the resolution on 300 (or 225, or 350, as you please)
you can see the largest size that file can be reproduced in its current
form. If the resulting dimensions are too small you have the option of
reclicking the "resample image" box and making the image any size and
resolution you want. Be sure to consider the different upscaling processes
at the bottom of the box as each affects different qualities of the image. "Rezzing"
up the image will not improve the quality and you may find that if you start
with a fairly small image and enlarge it significantly it will look rather
poor; either fuzzy, blurry or even pixilated. In many cases you can enlarge
a file by up to 50% without a serious downgrade in quality depending on the
content and quality of the original file.
So what about the 300dpi Jpeg? In an application that uses a 300ppi image we
would probably prefer to use a TIFF format file instead of a JPeg. As you will see
why, with just a few exceptions (see below) you would not use a "300dpi JPeg".
See additional step by step instructions further down.
JPeg is a
file format in which what would otherwise be a fairly large file is made
much, much smaller by compression. The compression process used by the JPeg
format analyses the pixels surrounding each pixel and acquires enough
information to recreate the image with only a fraction of the information.
This is called "Lossy Compression" and literally throws away a certain
amount of the data resulting in a pretty good looking image which may be
slightly blurry or have what are called compression artifacts. Some programs
allow the user to control this compression so an appropriate balance can be
made between damage to the image and the desired file size.
JPeg files are most typically displayed in low resolution on Televisions or
Computer Monitors. These displays typically present an image at only 72ppi.
They use illumination elements to create color using 3 filtered colors; Red,
Blue & Green (RGB). When all three colors are combined together they make
White, this is call Additive Color, in contrast to printed color (CMYK)
which if all are combined ideally make Black. CMYK makes white on a white
surface by applying no ink or color and is there fore referred to as
The JPeg format is ideal for display on screens in the content of Websites,
PowerPoint presentations and the like because it produces suitable files
that are easy to view on computers, are vivid in color and are relatively
small due to their compression.
When a JPeg is used for ink printing, particularly high quality printing
(high line screen) the damage caused by compression quickly becomes
apparent. The image may need to be enlarged if it was originally only 72ppi
resulting in a grossly pixilated image when printed in a magazine as you
may occasional see when advertisers supply their photos or logos from web
sources. A 300dpi version of the file may seem to be the answer,
but the JPeg format is not the ideal format for this type of application.
TIFF is an image format which can, but does not always use compression. When
compressed it is not like the destructive form used in JPeg. The standard compression
format of a TIFF file is not "lossy". The TIFF
compression scheme (most commonly LZW, named for the inventors Lempel, Ziv &
Welch) finds all duplicate elements in the file and replaces them with an
indication of multiples. In effect in stead of having 000000000 it is
replaced with 0x9. This means that no information is lost and the process is
referred to as "lossless compression". This allows users to modestly
compress an image file without damaging it. However the process of
compressing and uncompressing files does take time and computer power and as
such many printers and publishers prefer "uncompressed TIFF" format.
two aspect to color in relation to image files. One we have already
mentioned; RGB vs CMYK which I will talk about in a bit more detail in just
a minute. The other in the particular "flavor" of each of these which is a
factor in the range of colors that can be produced by the output device and
is related to the fine control of color which is called "Color Management".
What looks good one one monitor may not look the same on another. This is
because every monitor differs in its brightness, contrast and other
settings, some of which are adjustable and others that are not. Color
Management take into account the working color gamut during while it's being
worked in a program that uses color management including Adobe Photoshop.
The working "Color Space" indicates how wide a range of colors should be
used. This is particularly important when the final output of the image is
on a device which produces a much smaller range of colors. We start by
calibrating or standardizing the monitor the image is viewed on. Otherwise
if the monitor is slightly green and an image looks "neutral" it may
consistently output as slightly red or magenta. If we know the Profile of
the output device to be used in the final version of the image we can
account for this in the Color Space using our Color Management.
The range of color reproducible in RGB is significantly higher than can be
output in CMYK. Because of the limitations of reproducing color on paper
with ink the color spectrum is not as wide or vivid as RGB. A neon green or
super rich blue can be produced in RGB combining the three colors on the
monitor, but these same colors cannot be reproduced on paper using only the
4 color inks CMYK. By adding additional ink in the printing process a wider
gamut of color can be achieved and that's why we now see 6, 7 even 12 color
desktop printers. But even those cannot reproduce neon colors as they appear
on the monitor. To anticipate this smaller color gamut we can review the
images on screen simulating the smaller gamut of CMYK so we can anticipate
the limitations of the smaller gamut.
300ppi right? It is generally recommended to avoid using JPegs for print
applications because it is commonly and accurately assumed that most files
delivered as JPeg are not 300ppi, but the more typical screen resolution of
72ppi. However if you are using one of the programs which allow you to
control the amount of compression (such as Photoshop) you can produce a JPeg file which is
300ppi at a give dimension and save it in a JPeg format. The trick is to
select a compression of at least 8 and ideally 10 or higher if the scale
offers options over 10 (in Photoshop
CS4 the options go up to 12). This produces a file which is greatly reduced
in size, perhaps small enough to email, but has minimal compression damage.
Under no circumstances should you resave such a file as the compression
damage is multiplied each time it is resaved as a JPeg. Better to keep the original
file in a lossless format like TIFF and only make a separate Jpeg file when
it is at its final size and ready to send.
If you are
sending a file to an end user such as a printer or publisher and they know
that they are getting a properly setup file which is CMYK and you have saved
as a JPeg with minimal compression then sure, why not? But be aware that
most JPeg viewing programs (including operating system thumbnail previews) either cannot display a CMYK JPeg or do so with
gross color shifts which could be a problem if being reviewed by someone who
isn't aware that the file is CMYK and that is why the color shift in the
I had a
vendor call me for a client who needed to output graphics for a vehicle. I
asked the vendor what resolution he wanted the file. He said, "well, it
outputs at 1200dpi, can you give it to me at 1200dpi?" He was unable to open
the file I sent him because it was so large. He in fact did not need a file
at 1200dpi (ppi). The dpi indicated by the printer refers to the small dots
of ink and are not directly related to the file size itself. This type of
printer will make fine dots of ink for most any resolution, even low
resolution until the the square pixels become visible. For most desktop
inkjet printers a file that at final size is 150ppi will look just fine. For
high resolution inkjet printers of 18" or more in paper width 300ppi works
well, with 200-400ppi being a suitable range. You may be able to go even
lower, such as 150, 100, even 80 ppi or lower, but the resulting output may
appear blurry, pixilated, jaggy or pointillized to varying degrees depending
on the printer and the image. Commercial printers and
publisher generally need file sizes in relation to the line screen output
they are doing because they typically use technology involving an
ImageWriter and plates which transfer the ink to paper. Even plate-less
direct to press setups are usually based on a presumed line screen.
Many people have written to me "I found your article very helpful, except what I wanted to know is how do I make a 300dpi file". Below is the best I can offer.
How to make a 300dpi file from any file using Photoshop (don't have Photoshop? - sorry but you'll have to look elsewhere, but perhaps you better understand the concept now). Open your file in Photoshop. Under Image/ImageSize (Alt+Cntr+I) open the image size control dialog. Scale & Proportions should be checked. Resample should NOT be checked. In resolution type in "300". Your image is unchanged in its pixel size but is now 300dpi (ppi). You can Save As to lock the setting into a new file. Now if you want to upsize or downsize the file first "Save As" to a new name as you will now be changing your original. Then check the Resample box. Select the process under that (Bicubic Smooth for Enlarging, Bicubic Smoother for Reduction) and change one of the pixel dimensions or the document size dimensions. Everything else should stay proportional. Once you are satisfied resave the file, you are done, you have a new file sized to 300dpi and your original is unchanged (unless you forgot to "save as" a new name.)
If you find the above process too confusing, don't have Photoshop or are still at a loss you should consult a professional graphic designer, photographer, printer or production department where they will use your image for additional help.
If you are trying to change the dpi or size in Microsoft Word, Excel, PowerPoint, Publisher or most any consumer program other than Photoshop and some additional professional programs then you are probably using the wrong tools and again should consult a professional.
I hope that answers all of your questions about these topics. Please - do not call me about assistance with your files - if you must; please send an email. This article is helpful to 300-500 people a day (that's almost 10,000 people a month) and I will have to remove it if people keep calling me to explain it more clearly to them.
Those that do ask for assistance - I found that 90% of them are not using a program that will indicate the size of the file or are so lacking in experience in this field that this article offers no help - those folks need to hire a professional - a graphic designer, photographer or printer who works with these concepts everyday.
Thank you to all those who have sent thank you notes, I do appriciate your comments.
I welcome new work from new clients but due to our operating overhead our studio requires projects to start at a minimum of $600 to even consider, with $3000 being our average billing.
I hope you understand.