Image Size & Canvas Size - Photoshop Tutorial

Resolution Revisited

This Photoshop tutorial is related to the tutorial on resolution. Read it first to understand some underlying principles.

Resolution is a key to understanding image size and canvas size. This is because understanding resolution is key to understanding Photoshop as a whole.

Resolution, as a reminder, is how many pixels are in each inch of the photo. You can have a 4x6” photo with 100 pixels per inch (PPI) or a 4x6” photo with 300 ppi. One just has more “dots” in every inch, and therefore more detail.

Image Size

Image Size in Photoshop is measured in pixels and is expressed in Width x Height. Strictly speaking, the size of an image is in pixels, but resolution comes into play because Photoshop puts the image also into either inches, or centimeters (or points or picas for those of us who would ever use them).

So when you are talking about an image size, there are actually two possible ways to talk about the size of the image. In the end, they are basically the same, but the second has more context and is renamed “document size.”

These are:
Image Size: Pixel Dimensions
Document Size: Inch Dimension * Pixels Per Inch

Explanation: When talking of resolution I mentioned a 4x6” print that is 300 ppi. That is expressing the document size as the Inch Dimension and the Pixels Per Inch. If you take that expression and want to make it into just Pixel Dimensions, then do the following math:

(4 in * 300 pix/in) x (6 in * 300 pix/in) = 1200 pixels x 1800 pixels

That is the image size in Pixel Dimensions.

So when you say ‘A 4x6” image at 300 ppi,’ you are giving a mathematical expression. When you do the math, you get ‘A 1200 x 1800 pixel image.’ The two expressions mean the exact same thing in the end (in terms of actual number of pixels), but they have different contexts.

When you apply a resolution (let’s use 300 ppi) to the image that was 1200 x 1800 pixels, you get a 4x6” image at 300 ppi. Now it is more than just a bunch of pixels. You have a “goal” in mind, and that is a 4x6” image. You also have a “goal” of good detail, because you used an excellent resolution. This gives the image more context, and it is the expression of the document size in Photoshop.

This is because the same image (1200 x 1800 pixels) can be a 12x18” image if it is changed to 100 ppi. That is a very different image size in one respect (inches), but the exact same image size in another respect (pixels). Your “goal” now is a much larger print (document) with less detail in every square inch.

Image RE-Size

Resizing images is its own discussion. It is a very intense and even heated topic. So far I have alluded to changing the print size (in inches) of an image, and having the pixel image size stay constant (changing a 4x6” @ 300 ppi to a 12x18” @ 100 ppi, where the image stays at 1200 x 1800 pixels).

There are many more ways to change the image size. I can take away pixels, but keep the “aspect ratio” the same. I can try to add pixels and give it more detail. I can make one dimension larger while keeping the other dimension the same (make a person tall & skinny or short & fat like a fun house mirror).

The most hotly debated area of resizing is when you try to “add pixels” or “increase the resolution.” For example, you wanted the 12x18” @ 100 ppi to now have 300 ppi. If you do the math, you are trying to go from a 1200 x 1800 pixel image to a 3600 x 5400 image. That is a pretty tall order. Another way to express it is in mega pixels (or millions of pixels).

That would be going from a 2.2 MP image to a 19.4 MP image. To put that in context, as of today, camera phones can give you a (crappy) 2 MP image, but you have to spend almost $10,000 on a camera + lens to start getting images that start out at 20 MP.

Long story short: there are ways to get a bit more pixels out of an image. You can increase detail and pixel density. Going from 2 MP to 20 MP is basically impossible, though your CSI show will make you think otherwise. Moderate increases are possible with the right tools and techniques.

Those tools and techniques are the “hotly debated” topics.



Canvas Size

For most part, the canvas size and the image size are one in the same. But, we do have to distinguish between them.

I’m going to give you the punch-line first, and hopefully it will make sense as you read:

Image Resize: The image borders “stick” to the image and the image is pulled or squished with the borders.

Canvas Resize: The borders expand or contract without the image.


The image size has been detailed in the above sections. The canvas size is a little different. The canvas can be thought of as the border of the image.

When I resize an “image,” I make the entire file larger or smaller. When I resize the “canvas,” I enlarge or shrink the borders while the image stays the same size.

So, if I have an image of a flower, and the petals reach the edges of the image and almost touch the borders, then we can see the difference between canvas and image size.

Resizing the image will keep the image looking the same, it will just be a different size. Resizing the canvas will expand or contract the borders. If I make the canvas smaller, then the borders come in and the petals are clipped. If I make the canvas larger, then I am adding space around the image.

Now a confusing fact is that once the canvas is re-sized, everything resets with respect to image size. Your newly resized canvas is now also the size for the entire image. Yes, this is confusing. The video will help the most, but to explain with the example:

If the flower image was 2x3, that was the image size and canvas size (remember these two are almost always the same). I add 1” total (.5” to top, .5” to bottom, .5” to right, etc.) to both the height and width of the canvas. The image stays at 2x3”, but the canvas enlarges to 3x4” with 0.5” extra space around the original image.

A split second later, after the canvas resize is complete, you have a new image. Photoshop doesn’t keep tabs on the original image size. It is only concerned about the new image size that is a result of expanding the canvas.

In other words, the reason the canvas size and image size are mostly the same is because in the end, Photoshop only sees image size. It doesn’t see canvas size for the most part. So what is the difference?

The difference is only during the resizing effects. Both effects are going to affect image size. So you could say that both effects move the image borders (by either expanding or contracting them). The difference is this:

Image Resize: The image borders “stick” to the image and the image is pulled or squished with the borders.

Canvas Resize: The borders expand or contract without the image.

If that makes sense, you are on your way to “getting” Photoshop.

Flower image used in video: (c)2007 Derek Ramsey, taken at the Chanticleer Garden, cropped to fit the example.

Photoshop Tutorial- Image File Formats

So you have been playing around with Photoshop. It is kind of fun, your feet are getting a bit wet. Now you want to save what you have done, right? YES! You do. There is something I say a lot:

Save Early, Save Often.

(Edit: Unless you want to write over [and destroy] the original file, then you should think about saving a copy of the file instead of the original. Then the motto would be: Save Early, Save Often, Save a Copy).

It is a creed that everyone should live by. There is no “autosave” protection in Photoshop like you have in MS Word. If the program or computer crashes, you are out of luck.

Which Format?

So which format are you going to save your new masterpiece in? If you have opened up a digital photograph and done basic manipulations to it, then it probably started out as a .jpg (JPEG) and if you hit “Save” then it will probably save as a .jpg.

But is that the right choice? This might seem like an odd question to many people. As you work on most programs, you don’t often have to decide a file format. Well, with images you do if you want to get the most out of your hard work and save it in a way that will suit how you use the file in the future.

When you go to save a file (especially if you choose “Save As…” instead of “Save”), then you are confronted with as many as 20 or more file formats to save in. Some of them are antiquated and irrelevant to most uses. Some of these formats are for backwards compatibility (so you can save in that old format just in case you need to).

For 95% (or more) of you, the following formats are the only ones you really need to know how to use: .jpg (JPEG), .tif (TIFF), .psd (Photoshop Document), .gif, and one of the various RAW formats (.nef, .crw, .cr2, .raf, .mef, .raw, .tif [yes .tif is sometimes a RAW image], .orf, etc.).

JPEG (.jpg)

This format is, by far, the most popular image file format. All digital cameras save in this format, and only more professional (and a few consumer) cameras even give you the option of saving in another format.

The main reason for the popularity of the .jpg file format is because of the format’s ability to have the image go through compression. Compression is a way to make the unwieldy, bulky images much smaller so you can fit many more onto your camera’s storage chip, and onto your hard drive.

The amount of storage space saved is inversely proportional to the quality setting of the JPEG. In other words, if you set the JPEG to save at the highest quality (lowest compression, least loss of detail and data), then it will be a larger file than if you saved at a lower quality setting (more compression and loss of data).

I could get technical and lose you even more than I already have, or I could explain it using an analogy that might help.

JPEG images are like shelf-safe foods, and more specifically like pre-made meals that just need water. A manufacturer has made the food, dehydrated it to a degree, and then it made its way to you. Let’s use soup for this analogy. Taking out the water has made the soup easier to ship and store.

Now compare a dry soup mix (with little dry carrots and peas) to a condensed soup can (with mostly hydrated carrots and peas). Which is better quality when it has been prepared? I don’t know about you, but I prefer the condensed to the dry after they have been re-hydrated. The dry mix was cheaper to ship (due to weight), but so much was taken out of it as it was “compressed,” that it lost a lot of quality.

Now the video will get more technical (with demonstrations) than that, but it is an easy way to think about compression. The computer is removing information. Most of it can be regained (like just adding water), but if you take away too much, there is some detail that is not recoverable. Plus, like dehydrated and canned veggies, the photo can lose some of the original “texture” that it had. The video will explain more on that.

JPEG images can be saved on a quality scale of 1-12. Photoshop rates these as such:

1-4 = Low
5-7 = Medium
8-9 = High
10-12 = Maximum

As discussed, with each level there is a loss of data, but the higher you go the less it is to perceive. At about 9 you find a good file size to quality ratio. If you are most concerned about quality, go for an 11 or so. A 6 or 7 will give you more space savings, but it compressed the file so much that enlarging the image is more difficult.

Bottom Line: Do you want to save in JPEG?

Answer: Yes, it is not bad if you save at a good quality, or for your purposes. Which brings us to the purposes of a .jpg file.

Here are the purposes and situations where JPEGs are or are not suited for:

Digital Camera Capture: GOOD
The JPEG file format is what made digital cameras probable for consumer use. Not everyone could go around with a hard drive tethered to them, and that is what would have had to happen (until recently, when storage cards reached multiple gigabytes) back when cameras started going digital. Just make sure you save at the best quality setting on your camera (unless you are happy with sticking to 4x6 and 5x7 prints) because the lower quality JPEGs don’t enlarge well. You also should save at a high (or the highest) image size.* Why have a 6 mega pixel camera and save the images at 1 mega pixel (and therefore only be able to print 4x6’s)?

*By “size” here I mean actual pixels. Image size is the number of pixels (often rates in mega pixels). File size is how much space it takes on a hard drive.

At lower quality settings and smaller image sizes you are able to put more and more photos on one storage card, but it is at the detriment to your image quality. Test it out and see where your best image quality (and size) to storage space ratio is. It is often around 3/4 of the best quality and size, but everyone’s situation is different, so test it.

Image for the Web: GREAT
JPEG is optimal for the web when dealing with photos. Other file formats are better for illustrations and logos, but for photos, the .jpg is king. Again the whole file size to quality ratio applies. You can always test the results by saving a file, closing it, and then reopening it.

Another thing to think about for the web is image size (again, not file size, but image size – the number of pixels). You want to save the image as small as you can and still have it work for the use it is intended. If you are posting a file to a blog that is just for viewing, and not for you or friends to download and print, then you probably don’t need it much more than 640 x 480 pixels (0.3 mega pixels, or less than a third of a mega pixel). So why waste the time (and online storage space) by uploading a 5 mega pixel (MP) image?

Changing image size is a different tutorial altogether, but it does bring up another creed I live by: Keep an original, Save a copy!

To ensure that you don’t write over (and destroy) the original image with a changed file (and perhaps a web-sized 0.3 MP image that you now no longer have a 5 MP version of), do one of two things:

1) Start with a copied file
2) Save the manipulated image as a new file (choose “Save As…)

Number 1 is more recommended. That way you don’t accidentally write over the original.

Saving a File After Manipulating It: Sometimes GOOD, Sometimes BAD
After you have played around with an image, you can save it back as a .jpg, but that can be both good and bad.

BAD: It is bad when you are going to make more changes later and save it over and over again. Each save compresses it a little bit, and then a little bit more. More quality is lost with each save. Other formats are better for multiple saves: .psd and .tif.

GOOD: If you have made your changes and you are moving on. You don’t plan on making any more changes, then it is a nice way to store the final version in a spzec-saving way. If you want to continue to make changes later, but need a JPEG version now (for the web or printing at your local lab, etc.) then first save in a better format for later manipulation (.psd or .tif). Then you can save a .jpg version for use now.

That about covers it for JPEGs. It is a complicated and popular format, and one that you will run into the most. So it requires the most attention. The other formats won’t be as intensive.



TIFF (.tif)

TIFF is a loss-less file format. No compression is used (unless you do try to compress it in the save-options box, but if you wanted to do that, just use a JPEG). This means it is very high quality and very large.

A 9-quality JPEG from a 12 mega pixel image is between 1.2 – 6.5 MB (the subject matter is vital to compression, the more detail in the image, the larger it is when compressed). The same image as a .tif will be 34.9 MB, always. There is no compression and the quality is unchangeable, so the size of the image is directly proportional to the end file size.

TIFF is great for saving a file, opening it, manipulating it, saving it, opening it, manipulating it, saving it, etc. No detail is lost to compression for every save. So a .tif is recommended for a work in progress.


PSD (.psd)

The Photoshop Document (.psd) file format is the best for a “work in progress.” It is just like a TIFF, only it is native to Photoshop so it has added capabilities that a .tif file doesn’t have.

The major ability it is a bit better at layer saving.

Layers are an advanced Photoshop technique. Layers give you the ability to have layers of photographs or portions of photographs above and under each other. Think of putting a funny hat on the photo of your friend. You would grab a portion of another photo (that contained a hat) and then put it over the photo of your friend.

That portion of a photo is floating over the original photo, and it is in a separate layer. Layers are the key to dynamic editing in Photoshop, and they will be used extensively by me.

JPEGs can NOT be saved with layers. They have to be a flat photo. Period.

TIFFs can be made to save in layers, but they are not as good at it. Here is the difference, using the hat on the friend example.

The hat is a small object over the entire photo. Photoshop sees that small object as being small. It (in essence) saves two photos in one file. The two photos are the large background photo, and the small hat photo. It saves a .psd file that is a little bit larger than the original background photo’s file. So if the background file is 34.9 MB, the .psd file would be around 38 MB because the small photo object (the hat) is only a bit more info. (Note: to achieve this, you must un-check “Maximize Compatibility” as you save a PSD file).

On the other hand, a .tif file would also be saved as two photos in one file, but it would be saved as two complete photos. So if the original was 34.9 MB, the new .tif with two layers would be 69.8 MB. No matter that the second layer is really small, it is a complete new photo layer and is saved as such.

Compuserve GIF (.gif)

The GIF file is rarely used by most Photoshop users, but it is useful so I will mention it.

GIFs are compressed, but not like JPEGs. A .gif is compressed in the number of colors it uses. A JPEG can (and does) use all of the more than 16 million colors that a .tif or .psd image uses. Yes, 16.777 million colors! Having that many possible colors is necessary for an image to look real. Our eyes can see even more colors. But having that many possible colors per pixel is also a main reason digital photos are so big.

A .gif image if for those times you only need between 2 and 256 colors. Think of the ebay logo. It has 9 colors (the video will show that). Why “pay for” colors you won’t ever use? Make an image out of those 9 colors in a format that maximizes that use.

GIFs are therefore optimal for logos and other simple illustrations, especially if they are going on the web.

Well, that covers the most useful file formats. I didn’t think it would be this long, but the good old JPEG is one complicated beast.



RAW

Raw is a format I will only mention, but not delve into. This is because using Raw images is a more advanced way to capture (in the camera) and initially manipulate your images. Only advanced cameras (and a select few "point n' shoot" ones), even allow you to save in Raw.

So what is Raw? Well the short answer is that it is a non-compressed (or very slightly compressed) image format that is 2-5 times larger than a JPEG, and usually smaller than a .tif or .psd (because of the compression). Yet, even with the compression it is (for all intents and purposes) much better than a TIFF as a starting point.

The reason it is better is because of it's bit-depth. Let's not get too technical, and we'll say that an average Raw image has 1,073,741,824 possible colors per pixel (that's 1 billion possible colors) to the normal TIFF and JPEG's 16.8 million colors.

Thos extra shades mean that it can capture subtle (very light or very dark) pixels where a JPEG would see white or black. If you over expose an image, the JPEG will have pure white areas where there should be detail. A Raw image will see subtle detail that you can "pull back" by darkening the image.

I won't even bother with a video for Raw format. That will be a different post altogether, but I'll leave with a video demonstrating how to save in the separate formats.

Getting Around Photoshop

Photoshop is (in many ways) like most programs. It has menus at the top as well as a large open area where you do all of your work. It does, however, have a few additional areas that you will need to become acquainted with. These include the tools and palettes.

I will cover the five major areas in the Photoshop workspace. These are the Canvas (File), Menus, Tool Box, Tool Options Box, and Palettes.


Canvas/ File

The canvas is where you do all of your work. It is very often a photograph that you have opened. It can also be called a “file.” In other words it is what you are working on.

The canvas should not be confused with the background of the program. Mac users don’t have a program background, so they are probably confused already as I talk of one. But PC versions of most programs do have a program background.

The canvas/ file floats above that background and there can be multiple files open at the same time floating above and below each other.

Some notable features of the canvas are that it is its own window that can be enlarged, closed, minimized, etc. Along the top of the canvas is the file name, how zoomed in it is (in percentage), the color space, and the bit depth. That looks like something like this: File Name.jpg @ 100% (RGB/8).

Color space and bit depth are advanced concepts. For now just know that RGB color space at 8 bits/ channel (RGB/8) is normal for about 90% of normal photographic manipulation.

The Canvas can have a ruler (as in the video example). The ruler can be in inches, cm, percentage, pixels, etc. It can be turned on or off in the “View” menu. A grid is also available, but not recommended

The canvas does have one more option. It is an information display box at the bottom of the window, just to the left of the scroll arrow. There is a right-facing triangle that, when clicked on, can change the information displayed in a box left of that arrow.



Menus

The program menus in Photoshop are where you find most of the effects that you can apply to your image. You will also find the usual program commands such as: Open, Save, Print, Cut, Paste, etc.

These menus have so many uses that it would take weeks to explore all of them. The video does a quick overview of the menu groups.



Tool Box

Tools are mainly used for selective changes that you apply to a certain area. When you select a tool, your mouse becomes that tool. It is as though you are picking up and holding a tool out of a tool box.

Because you are now able to “wield” a tool, you are able to manipulate the image in specific areas. This is important if, for example, you wanted to brighten just one area and not the entire image.

This is the main difference between the effects you find in the program menus and the effects you can achieve using the tools in the tool box. The effects in the program menus are (for the most part) effects that you apply to the image as a whole. It is in the menu that I would find the effect to brighten the entire image. However, using the “Dodge” tool from the tool box, I can lighten a specific area using a “brush.”



Tool Options

Tool options appear just under the program menus (unless that “window” has been closed, it can be brought up again by going to the Window menu and selecting “Tool Options). This is where you can fine-tune your tool and make it act how you need it to.

Often you can increase or decrease the intensity of the tool, and change how large of an area it affects at a time. The tool options window is an important place to start right after selecting a tool.



Palettes

Palettes can be moved anywhere (as can the tool box and the tool options window), but generally they are found to the far right of the program window.

Palettes are where you store extra windows. These windows usually contain extra options and tools that are connected to either tools from the tool box, or effects found in the menus.
Just like an artist’s palette is customized for their workflow, you open the palettes that are most useful to you. If you are always needing to select colors to use, then you will have a color palette open (it is an extension of the color tool in the tool box).