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What is image size?

From: Photoshop CS5 One-on-One: Fundamentals

Video: What is image size?

In this exercise, I am going to lay out the basic concept of image size inside of Photoshop. This is one of these core topics that you've got to wrap your brain around before you can make any meaningful sense of the program. So here is how it works. Image size is the dimensions of your image, that is how many pixels wide, and how many pixels tall. And we care about pixels more than the other measurements, more than inches and centimeters, and all that stuff that means something in print, but doesn't have any meaning on screen.

What is image size?

In this exercise, I am going to lay out the basic concept of image size inside of Photoshop. This is one of these core topics that you've got to wrap your brain around before you can make any meaningful sense of the program. So here is how it works. Image size is the dimensions of your image, that is how many pixels wide, and how many pixels tall. And we care about pixels more than the other measurements, more than inches and centimeters, and all that stuff that means something in print, but doesn't have any meaning on screen.

So this very simple concept. How wide is the image? How tall is the image in pixels? That's image size. But it begs a lot of questions. For example, how many pixels do you need? How many pixels should you capture with your digital camera? How many pixels should you be scanning? What resolution value should you use? How many pixels do you need for smooth output? What if you don't have enough? Can you add more pixels inside Photoshop? Should you ever subtract pixels or should you change the resolution value and leave the pixel count alone? And what is resolution anyway? Well, sorry to fire so many questions at you, but these are the questions that we will be answering over the course of this chapter.

Now if you are working along with me, I've got a piece of artwork for you. It's called Shepherd and small flock.tif. And when I say small flock, I don't necessarily mean a small flock of sheep. I mean a small flock of pixels, because there is not many pixels at work inside this image. Now, this is a piece of artwork I created years ago. It's a kind of murder mystery because here's the shepherd up here. Here is the skeleton on top of this arch. And then his clothes were stuffed into a scarecrow, and we have the sign that says Killer indicating that the scarecrow is the killer, but really the sheep did it.

Anyway, that's the subject of this artwork. The content is pixels. Now, we are seeing this image at the 100% zoom level, meaning Photoshop is devoting an entire screen pixel to each and every image pixel, and we're seeing almost the entire image in the Full Screen mode here, just a little bit of the perimeters being cut off. So, if we're looking at 100% then we're seeing everything there is inside this image. In other words, we're not going to find anymore detailed information inside of this artwork.

For example, if I press and hold the Z key to get the Zoom tool and then I drag to the right in order to take advantage of that scrubby Zoom function in CS5, I'm zoomed way in on the scarecrow's face and yet it doesn't look anymore like a scarecrow than it did before. We're not seeing anymore definition to the line art in other words. Instead, we're just seeing these big huge pixels divided by the pixel grid. Incidentally, if you don't know what a pixel is, it's a colored square. So each and every digital image you see is this incredibly complicated mosaic and nothing more.

In fact, you may know that Photoshop is the most popular program from Adobe. So the other teams inside Adobe like to razz the Photoshop guys about what's the big deal! All you guys do is recolor pixels. At the end of the day, that's true. Photoshop just happens to be an extremely complex, extremely powerful pixel re-coloring machine. What we need to know now is how many pixels are available to us. So I am going to go over to this I button here, and click on it to bring up the Info panel.

You can also go to the Window menu and choose Info or press F8. Now, Info is a terrific panel for analyzing an image. You can see the color of the pixel under your cursor represented in RGB and CMYK by default. But you can change those around if you want to. You can also see the co-ordinate position as measured in pixels in my case and hopefully yours as well, that XY position right there of your cursor. Then you can see the width and height of a selection outline, plus we are going to see the document size and a description of how to use the Active tool.

Although, I don't find that last item to be very helpful, but the document size is pretty helpful. We're seeing that it's 1.9 megabytes in Photoshop's memory in RAM, and that's not very large. Now, that's big for a web graphic, but it's dinky by print standards and it's definitely small enough to email to somebody, which is a good thing and it's not going to slow Photoshop down. Photoshop has no problem with 2 megabyte images like this. Anyhow, there's more information to be had, and we can get to it by clicking on this menu icon and choosing panel Options.

What I am going to do, first of all, I want to confirm that Ruler Units is set to Pixels. You'll need it to be set to pixels throughout this chapter but I recommend you have your units set to pixels always in Photoshop. Next, I'm going to turn off those tool hints because I don't find that to be helpful at all, and I am going to turn on Document Profile which is the color profile that's associated with the active image, and Document Dimensions which will be the image size itself, and then if you like to know what's going on underneath Photoshop's hood, you may want to turn on Scratch Sizes.

And that's going to tell you the size of the scratch disk file on your hard-drive. Then go ahead and click OK. Notice the tooltips have gone away. There is the scratch size and very briefly what's happening there is in the event that Photoshop tops out in RAM, you open a big image, lots of layers, Photoshop is trying to keep track of all the history, and it's too much to store all that information in memory. So it has to go to a scratch disk file on the computer's hard-drive. And the size of that file is going to change over time, but mine has grown to 1.4 gigs.

Currently, I am only taking advantage of 457 megabytes of those 1.4 gigs. Where things become a problem is if this number starts becoming very large or these two numbers are very close to each other, it's not something you should worry about. It's just something you should know in case the program is running very slowly, and when that starts happening, you might just want to restart Photoshop. You don't have to reset the preferences or anything. You might just want to restart the program in order to clear out the memory. Worst case scenario, every once in a while you have to restart your machine.

Anyway, back to the image size stuff. This image is not so big it's going to hurt anything. Next, we have the Adobe RGB (1998) profile. That's how we established our color settings long ago. Then you can see that the image measures 993 pixels wide by 668 pixels tall. Now, if you do that math, you just multiply those two numbers together. You discover that total number of pixels inside this image is 663,324, so nearly 700,000 pixels which sounds like a lot.

However, where pixels are concerned, that's not very much. Bear in mind that's not even a mega- pixel which is a million pixels, and your digital camera shoots lots and lots of mega-pixels. Next comes this value, 100 ppi, 100 Pixels Per Inch, and that's the print resolution. It only matters for print and it also happens to be a linear measurement. Meaning that an inch will contain 100 pixels wide, and 100 pixels tall. So 100x100. That is 10,000 pixels fit in a square inch.

That may sound once again like a ton of pixels but it's not nearly enough for professional printing. So what we have here is an exceptionally low resolution image. How do we go about gaining more pixels as well as gaining more clarity? Well, that's a question I will begin to answer in the next exercise.

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This video is part of

Image for Photoshop CS5 One-on-One: Fundamentals
Photoshop CS5 One-on-One: Fundamentals

195 video lessons · 73641 viewers

Deke McClelland
Author

 
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  1. 39m 52s
    1. Welcome to Photoshop CS5 One-on-One
      1m 49s
    2. Making Photoshop your default image editor
      7m 43s
    3. Installing the DekeKeys keyboard shortcuts
      8m 10s
    4. Remapping Mac OS shortcuts
      7m 37s
    5. Installing the Best Workflow color settings
      4m 31s
    6. The color settings explained
      6m 54s
    7. Loading the CS5 color settings in Bridge
      3m 8s
  2. 53m 36s
    1. There is nothing you can't do
      2m 1s
    2. The power of Photoshop
      4m 43s
    3. Duplicating a layer
      4m 49s
    4. Liquifying an image
      4m 43s
    5. Adding a layer mask
      5m 54s
    6. Loading an alpha channel
      7m 42s
    7. Selecting with Color Range
      4m 10s
    8. Making a Hue/Saturation layer
      2m 53s
    9. Luminance blending
      7m 21s
    10. Mask density
      5m 9s
    11. Making a knockout layer
      4m 11s
  3. 51m 23s
    1. The best way to work
      41s
    2. Setting General preferences
      5m 33s
    3. Changing the pasteboard color
      5m 41s
    4. File handling, performance, and units
      7m 25s
    5. Touring the Photoshop interface
      11m 5s
    6. Creating and saving a workspace
      7m 21s
    7. Changing settings and updating the workspace
      6m 4s
    8. Resetting the preferences
      7m 33s
  4. 2h 46m
    1. The amazing Adobe Bridge
      1m 17s
    2. Making a new image
      5m 11s
    3. Opening an image
      7m 7s
    4. Opening and closing multiple images
      5m 24s
    5. Opening a problem image
      4m 23s
    6. Adding file information
      8m 37s
    7. Introducing Adobe Bridge
      7m 37s
    8. A whirlwind tour of Bridge
      7m 21s
    9. Adjusting the interface and thumbnails
      8m 18s
    10. Using the full-screen preview
      8m 5s
    11. Rotating images on their sides
      5m 38s
    12. Assigning star ratings and labels
      8m 40s
    13. Filtering thumbnails in the Contents panel
      9m 13s
    14. Moving, copying, and deleting files
      6m 34s
    15. Creating and assigning keywords
      6m 38s
    16. Searches and collections
      7m 3s
    17. Batch-exporting JPEG files
      8m 57s
    18. Batch-renaming
      7m 15s
    19. String substitution and regular expressions
      8m 50s
    20. Grouping images into stacks
      7m 21s
    21. Comparing images in Review mode
      5m 58s
    22. Playing images in a slideshow
      4m 49s
    23. Customizing and saving the workspace
      7m 17s
    24. Using Mini Bridge in Photoshop CS5
      8m 36s
  5. 1h 1m
    1. Learning to swim inside an image
      37s
    2. The tabbed-window interface
      5m 19s
    3. Arranging image windows
      4m 26s
    4. Common ways to zoom
      5m 31s
    5. New zoom tricks in Photoshop CS5
      4m 24s
    6. Hidden old-school zoom tricks
      4m 34s
    7. Scrolling and panning images
      4m 8s
    8. Viewing the image at print size
      6m 42s
    9. The Navigator and "bird's-eye" scrolling
      2m 56s
    10. Nudging the screen from the keyboard
      2m 39s
    11. Scroll wheel tricks
      3m 41s
    12. The Rotate View tool
      3m 36s
    13. Cycling between screen modes
      6m 17s
    14. Using the numerical zoom value
      6m 14s
  6. 1h 6m
    1. Imaging fundamentals
      58s
    2. What is image size?
      7m 45s
    3. The Image Size command
      6m 0s
    4. Selecting an interpolation option
      4m 56s
    5. Upsampling versus "real" pixels
      5m 22s
    6. The penalty of pixels
      5m 35s
    7. Print size and resolution
      7m 26s
    8. Downsampling for print
      6m 39s
    9. Downsampling for email
      7m 28s
    10. Options for upsampling
      8m 13s
    11. Better ways to make a big image
      6m 1s
  7. 44m 43s
    1. Frame wide, crop tight
      1m 2s
    2. Using the Crop tool
      8m 8s
    3. Fixing out-of-canvas wedges
      5m 31s
    4. Crop tool presets
      6m 53s
    5. Previewing the crop angle
      4m 24s
    6. The Crop command
      4m 47s
    7. Straightening with the Ruler tool
      4m 18s
    8. Cropping without clipping
      5m 1s
    9. Perspective cropping
      4m 39s
  8. 1h 41m
    1. Making drab colors look better
      1m 20s
    2. Brightness and contrast
      4m 10s
    3. Adjusting numerical values
      4m 26s
    4. Introducing adjustment layers
      5m 17s
    5. Editing adjustment layers
      2m 51s
    6. Saving adjustment layers
      4m 35s
    7. Adding a quick layer mask
      4m 23s
    8. Introducing the Histogram
      4m 34s
    9. Working with the Histogram panel
      6m 27s
    10. Using Color Balance
      7m 18s
    11. Introducing the Variations command
      4m 51s
    12. Luminance and saturation controls
      3m 54s
    13. Fading a static adjustment
      3m 21s
    14. How hue and saturation work
      4m 28s
    15. Rotating hues and adjusting saturation
      6m 4s
    16. Creating a quick and dirty sepia tone
      4m 42s
    17. Adjusting hues selectively
      5m 32s
    18. The Target Adjustment tool
      4m 24s
    19. Photoshop CS5 Target Adjustment enhancements
      53s
    20. Adjusting the color of clothing
      8m 44s
    21. Enhancing a low-saturation image
      4m 23s
    22. Refining saturation with Vibrance
      5m 1s
  9. 1h 57m
    1. Photoshop versus the real world
      1m 21s
    2. Meet the selection tools
      10m 26s
    3. Marking the center of an image
      4m 9s
    4. Drawing a geometric selection outline
      4m 45s
    5. Blurring a selection outline with Feather
      6m 8s
    6. Copy and paste versus drag and drop
      5m 31s
    7. Creating a graduated selection
      4m 29s
    8. Aligning one image with another
      4m 45s
    9. Accessing the Move tool on the fly
      3m 34s
    10. Invert and Match Colors
      5m 4s
    11. Matching colors selectively
      3m 52s
    12. Feathering and filling a selection
      5m 14s
    13. Dressing up a composition with effects
      5m 34s
    14. The incredible image rotation trick
      2m 18s
    15. The Magic Wand tool
      4m 12s
    16. Tolerance and other options
      7m 7s
    17. Grow, Similar, and Inverse
      5m 39s
    18. Quick selection and the Magnetic Lasso
      7m 27s
    19. Evaluating a selection in Quick Mask
      8m 52s
    20. Saving and loading selections
      6m 14s
    21. Placing an image with a layer mask
      3m 23s
    22. Eliminating edge fringing
      7m 43s
  10. 1h 58m
    1. Brushing to correct
      56s
    2. How brushing works
      4m 52s
    3. Working with spacing
      7m 32s
    4. Changing size and hardness
      7m 45s
    5. The heads-up Color Picker
      7m 17s
    6. Flipping a mirror image
      3m 33s
    7. Setting the source for the History brush
      3m 42s
    8. Brightening details with the Dodge tool
      7m 49s
    9. Darkening details with the Burn tool
      3m 5s
    10. The Sponge tool
      4m 29s
    11. Backing off edits
      8m 4s
    12. Patching eye bags
      8m 57s
    13. Evening out flesh tones
      7m 23s
    14. Smoothing away whiskers
      7m 41s
    15. Reducing shadow noise
      7m 0s
    16. How healing works
      4m 40s
    17. The enhanced Spot Healing brush
      4m 52s
    18. Using the better Healing brush
      4m 23s
    19. Introducing the Clone Source panel
      3m 49s
    20. Cloning from one layer to another
      5m 30s
    21. Working with multiple sources
      4m 44s
  11. 1h 23m
    1. The layered composition
      1m 0s
    2. Making a new background layer
      6m 58s
    3. Working with "big layers"
      6m 24s
    4. Move, Duplicate, and Scale
      4m 11s
    5. Transforming a copy and repeat
      5m 15s
    6. Stacking order and eyedropping a layer
      5m 15s
    7. Adjusting multiple layers at once
      4m 22s
    8. Switching between layers
      4m 56s
    9. Making a digital star field
      5m 9s
    10. Blend mode and clipping mask
      4m 50s
    11. Dragging and dropping from your desktop
      4m 38s
    12. Black + Lens Flare = glow
      6m 16s
    13. Locking transparency
      5m 42s
    14. Adding gradient layers
      8m 12s
    15. Stacking an adjustment layer
      4m 12s
    16. Adding shadow and stroke
      6m 9s
  12. 1h 17m
    1. Outputting from Photoshop and Bridge
      1m 32s
    2. Printing an RGB composite
      5m 31s
    3. Customizing the subjective print file
      3m 15s
    4. Gauging print size
      5m 35s
    5. Scale, position, and page orientation
      5m 6s
    6. Three important printing curiosities
      4m 41s
    7. Introducing the Output options
      5m 34s
    8. Establishing a bleed
      5m 52s
    9. Using the Color Management options
      7m 21s
    10. Generating a PDF contact sheet
      6m 18s
    11. Creating a contact sheet template
      6m 8s
    12. Saving and opening a PDF contact sheet
      4m 18s
    13. Introducing the Web Gallery
      7m 53s
    14. Exporting and editing an HTML site
      3m 58s
    15. The Airtight Photocard site
      4m 56s
  13. 1h 9m
    1. Rules of the web
      1m 1s
    2. Introducing web graphics
      6m 59s
    3. A first look at Save for Web
      5m 47s
    4. Scaling a layered image versus a flat one
      7m 30s
    5. Incremental downsampling
      3m 1s
    6. Adding text, bar, and stroke
      4m 24s
    7. Assigning copyright and metadata
      6m 21s
    8. Comparing GIF, JPEG, and PNG
      4m 59s
    9. Determining the perfect JPEG settings
      6m 31s
    10. Saving metadata
      3m 52s
    11. Working with an unprofiled RGB image
      4m 35s
    12. Downsampling graphic art
      4m 49s
    13. Saving a GIF graphic
      6m 1s
    14. Antiquated GIF versus the better PNG
      4m 6s
  14. 1m 37s
    1. Until next time
      1m 37s

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