PHOTOSHOP:ANINTRODUCTION

DIGITAL SESSIONSWELSH SCHOOL OF ARCHITECTURE - CARDIFF UNIVERSITY

WASSIM JABI AND SERGIO PINEDA

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Digital Sessions

WELSH SCHOOL OF ARCHITECTURE – CARDIFF UNIVERSITY

DR. WASSIM JABI AND MR. SERGIO PINEDA

PHOTOSHOP: AN INTRODUCTION

WHAT PHOTOSHOP CAN DO FOR YOU

With Photoshop you can repair, adjust, create, combine and calibrate images. You

can also apply an almost endless range of effects.

The fundamental building block of Photoshop’s universe is the pixel. Pixels are square,

they each contain a single colour, there is no space in between them, and they are

usually very, very small (unless you zoom-in to look at them!).

In Photoshop you can open existing images (from digital cameras, online sources,

etc) or create a new image. Within it’s interface you can alter images (colour,

contrast, hue, saturation, etc), fix damages (scratches, etc) insert images inside

other images, cut out shapes of objects, add backgrounds, alter foregrounds, and

apply a huge amount of effects on images in general.

THE PHOTOSHOP INTERFACE

The main controls in Photoshop appear along the top of the screen, where you will

find a group of menus, and floating in the screen is the Toolbox (generally on the left

hand side). The Toolbox and many other menus and options can be turned on/off

under the Window menu – any ticked names on this list are open in your screen (if

you cannot see a menu that is supposed to be open, it is probably hidden under

something else).

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SUGGESTED WINDOWS TO HAVE OPEN AT ALL TIMES:

• Toolbox

• Layers

• History

(Note: depending on what you are working on, you might want to keep some other

windows open during a given session, like Paragraph, etc).

RESOLUTION AND IMAGE SIZE

As mentioned above, images in Photoshop are made out of Pixels. Pixels are very

small square areas with a single tone and no space in between them.

To specify the size of an image, Photoshop requires you to define the height and

width of the image, and the default way of doing this is by defining it in pixels. For

example, if you go to ‘File>New’ you will be prompted with the following window:

Here you can insert specific dimensions in terms of pixels to define width and height

(in the case above, 1000 by 1000). But this is not very specific in terms of the size

of this image of the time of printing.

The obvious question is: How do you know the size of this image at the time

of printing?

In the drop down menu where it says ‘pixels’ choose ‘cm’.

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Now we know that the image will be printed at 35.28 cm square. This means that a

horizontal line of 1000 pixels will be distributed along those 35.28 cm. This type of

measurement refers to the ‘Resolution’ of the image. In terms of how many pixels

there will be per inch, Photoshop is telling that this corresponds to 72 pixels per inch

(Resolution is commonly referred to as DPI, dots per inch).

Although 72 DPI (72 dots in one inch) may seem as many dots, the human eye can

distinguish dots printed at this resolution – it will look ‘pixelated’. In this sense, if you

wish to print an image, and expect it not to look ‘pixelated’ (i.e. you wish the human

eye not to perceive the pixels) you need to print at a higher resolution. A good

quality image is generally printed at 300 dpi. Now, if we modify the case above so

that it distributes 1000 pixels at 300 pixels per inch, how big is the image in

centimetres?

Photoshop gives us the answer! 8.47 cm. So, although the image seemed quite large

at 72 DPI (more than 35 cm), if you want to print it at a good resolution (300 dpi) it

will only be 8.47 by 8.47 cm.

You can work the dimensions the other way round: imagine that you wish to print an

image of 20 cm by 20 cm to print (300 dpi):

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In effect, you can now ask Photoshop the dimension of this image in pixels:

If you are working with an existing image, and wish to know it’s size/resolution, go to

‘Image>Image Size’. The following window will open:

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The top half of the Image Size window shows the image’s width and height, either as

a percentage or in pixels.

The lower half of the window shows the image’s width and height in units, such as

centimetres, and the resolution. Make sure the units for the resolution are dots per

inch and not dot per centimetre.

Below this area are 2 very important check boxes: ‘constrain proportions’ and

‘resample image’. Keeping only the ‘constrain proportions’ box checked means that

the width, height and resolution of the image are linked to each other. Then,

whichever of the three is changed, the other two automatically adjust to maintain

not only the proportions but also the file size. In this scenario, the number of pixels in

the image (shown in the top half of the window) becomes locked and cannot be

changed).

If the ‘resample image’ box is also checked, only the width and height are linked. This

prevents the image from becoming distorted, but allows you to change the

resolution and therefore the file size.

COLOUR MODES

Photoshop (and in general, pixel images on computers) run on 4 different colour

modes:

• Bitmap: pixels can only be of 2 different colours. Used very frequently in early

use of computers, not very much used for design today.

• Greyscale: Is what is generally understood as a ‘black and white’ image. In

fact, these images have a full range of grey tones, with black at one end of

the spectrum and white at the other end.

• RGB: Means ‘red, green, blue’. Refers to the way in which screens (tv screens,

computer monitors, etc) produce millions of colours by producing

combinations of these 3 colours of light. In essence, a tv screen for example

is made out of very very small light emitters, which can each produce a red,

blue or green tone. These emitters are so small that our eyes don’t see that

they are just blue, or just red – we perceive combinations of them in the form

of yellow, purple, brown, etc. RGB is ideal as a colour mode if you expect your

work to be mainly appreciated on a screen (for example, online, etc).

• CMYK: Means ‘cyan, magenta, yello, black’. Refers to the ink tones used by

plotters and printers to produce millions of tones on prints. In this case,

instead of combining tones of light, a printer combines tones of pigment.

CMYK is an ideal colour mode if you expect your work to be mainly

appreciated in a printed form (for example, as prints pinned up on a wall).

When you create a new image in Photoshop (‘File>New’) you will be asked what kind

of colour mode you wish to use:

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The colour mode ‘Lab Colour’ is not of common use.

In spite of the clear differences between an RGB, CMYK or greyscale image, they are

all transferable to each other colour mode. At the time of transferring, though, you

may loose information. For example, if you have a full colour image of the sea (with

blue, green and aqua tones) and you convert it to greyscale, you will loose all the

colour information, and it will all appear as tones of grey.

To convert an image from one colour mode to another, go to ‘Image>Mode’ and

choose your mode of choice.

LAYERS

In Photoshop you can have multiple images overlaid in one same file, as if each one of

them were a cut out piece of paper on a table. The difference is, in Photoshop, each

one of those layers can be partially transparent, or entirely transparent, and they can

all be modified independently or as a whole.

To open the layers window, go to ‘Window>Layers’.

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To modify a specific layer, click on it – it will be highlighted (as Layer 2 in the image

above). To hide a layer, click on the ‘eye’ symbol next to it. To make a layer partially

translucent, change the ‘Opacity’ percentage. To delete a layer, click on it and drag it

to the ‘rubbish bin’ icon at the bottom of the layers window. To create a new layer,

click on the ‘Create a New Layer’ icon:

To duplicate a layer, right click on it (PC) and select the ‘Duplicate Layer’ option. This

will create a duplicate that is identical to the first layer. (For Mac, press Control and

then click on the layer you wish to duplicate, then select the ‘Duplicate Layer’ from

the menu that appears).

Layers appear as in a stack. The top layer in the stack is equivalent to a piece of

paper at the top of a stack of sheets on a table, i.e., it will be fully visible. The layers

underneath this upper layer may be covered by the layers above them.

Layers can be merged by choosing them and then going to ‘Layer>Merge Layers’.

Different image formats preserve layers, or don’t! If you expect to continue working

on an image and require it’s layers to be distinct entities, you should save your work

as a PSD file. This type of file will preserve the entirety of your layers, but it will not

be easily imported into other programs or for use online, for example.

If you consider that your work on the image is finished and you wish to print it, or

put it online, you should save your file without layers, as a ‘flattened’ image, this is,

without any layers.

To flatten an image, go to ‘Layer>Flatten Image’. You can then save the image as

jpg, tiff, and other formats.

Tip: When working with multilayered images, always keep a version of them as a PSD

file, with the entire group of layers, in case you need to modify it in the future. For

prints and online uploading, you can always save versions of the image as JPG, etc.

ZOOMING AND SCROLLING

Several images can be open at one same time in Photoshop, but only one image can

be ‘active’.

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To explore using the zooming/scrolling options, open any image (jpg, tiff, psd, etc).

Zoom in:

Whilst on the image you just opened, hold down ‘apple/control + spacebar’ and click

and drag with the mouse a rectangle over an area you would like to zoom in to.

Release the button and that area will fill the screen.

Zoom out:

Hold down ‘alt + spacebar’ and click the spacebar (zoom out in increments).

Hold down ‘apple/control’ and tap the ‘-‘ (hyphen or minus) (zoom out in

increments).

Hold down ‘apple/control + 0’ (zero) (zoom straight back out to see the entire

image).

Scroll:

Use when you have zoomed into a specific location and you cannot see the entire

image

Hold down the spacebar and drag with the mouse.

THE MARQUEE SELECTION TOOLS

Photoshop lets you select a specific part of an image and copy it, transform it,

modify it, erase it, etc, without affecting the rest of the image. The most direct

tools to perform selections are the Marquee tools.

There are four tools on the Marquee Tool flyout:

• Rectangular

• Elliptical

• Single Row

• Single Column

The latter two select a single row or column across the whole image, When using

these tools, you can add subsequent rows/columns of pixels by holding down the

shift key and doing further selections.

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For rectangular selections, pick the Rectangular Maquee tool and click and drag on

the image to define a selection.

If you want to add rectangular areas to your selection, hold down the ‘shift’ key and

a small ‘+’ sign appears next to the cursos. Click and drag the mouse to choose other

areas – these will be added to your original selection. If you wish to subtract from the

selection, hold down the ‘alt’ key and a small ‘-‘ sign appears instead. You are now

able to click and drag to subtract from the selection. This lets you carve out shapes

from the selection.

DESELECTING

By holding ‘apple/control + d’ (or clicking on the menu ‘Select > Deselect’ ) your

selection will vanish.

LASSO TOOLS

By clicking and holding on the second button down on the left of the Toolbox, you

will see the flyout for the Lasso, polygons and magnetic tools.

If you choose the lasso tool you will be able to click and drag in the image to create a

shape (freehand). When the mouse is released, a selection of that shape appears. To

add shapes, just hold the ‘shift’ key. To subtract hold the ‘alt’ key.

The polygonal lasso tool let’s you choose specific points in the image – it creates

straight lines in between the points you define. To close the shape, click as close as

possible to your initial point. An area will be defined now as a selection.

The Magnetic lasso tool may be a valuable time-saver. Select the tool and in the

Control Bar set a brush size, a tolerance and an anchor point frequency. Drag the tool

along the edge of the object you wish to select. If the brush size is small and you

drag reasonably accurately, the resulting selection will be quite accurate. The anchor

point frequency determines how often an anchor point is placed on a path. If you

think a path could do with an additional point, you can click to place one at any time.

As before, when the cursor returns near the starting point, it changes symbol and

you can click to complete the selection shape.

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With both the Polygonal and Magnetic tools you can ‘undo’ parts of your selection:

Click the delete key, and then redraw!

THE MAGIC WAND

Uses a tolerance setting to do automated selections when figure and foreground and

clearly different. For example, if you have a photo of an object in front of a wall with

a uniform colour, and you wish to replace the wall for a forest, you can select the

magic want tool and then click anywhere in the background of the image. This will

automatically select the entirety of the wall, leaving the object clearly outlined. At

this point you would be able to delete the background and then replace if (for a

forest, a gradient, or anything of your choice). The magic wand tool also has a

tolerance which can be changed at any time during the selection process.

SAVING AND LOADING SELECTIONS

When selections are lengthy and involve many steps, it is important to save them

regularly, even whilst they are being fine tuned. To save the selection go to

‘Select>Save Selection’, which opens the Save Selection window. If additional edits

are then made to that selection, they can be incorporated into the save selection by

going again to ‘Selection>Save Selection’ and choosing the same channel (rather

than creating a new one). You will be offered the option of replacing, adding to or

subtracting from the previously saved selection.

SELECT BY COLOUR

In Photoshop you can select by ‘Colour Range’. This tools is very useful if, for

example, you are working on an image of a tree with a background made out of an

even blue sky, and you wish to select each and every blue pixel that forms the sky

(even if these pixels are not reachable with a Magic Wand operation, as described

above). You can go to ‘Select>Color Range’, and then click on the blue sky. The tool

will select any pixel that shares the same tone, within a given range (which can be

modified within the Colour Range tool).

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INVERSE SELECTION

This tool is enormously useful. Imagine that you are again working with the image of

a tree in front of the even blue sky, but instead of selecting the sky, you wish to

select the tree. The problem is that you won’t be able to choose the tree through

the ‘Colour Range’ tool because it is made out of multiple tones (brown, green, etc).

Instead of choosing one by one each and every leaf that make up the tree, you can

select (by Colour Range for example) the sky, and then go to ‘Select>Inverse’. This

will select every pixel that is not the sky, and will deselect every pixel forming the

sky. The short cut for this is ‘apple/control + shift + i’.

HISTORY AND UNDO

As most programs, in Photoshop you can ‘undo your last action’ with ‘apple/control

+ z’. But this will only let you undo one action.

As opposed to this rather limited ‘undo’ tool, Photoshop has a window

(‘Window>History’) by which you can track many previous actions and jump directly

to any one of them by just clicking on them.

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As a default, this window retains the last 20 operations performed on an image. You

can modify this – to go back up to 99 operations go to (Mac)

‘Photoshop>Preferences>General’ or (PC) ‘Edit>Preferences>General’ and reset the

window to record the number of operations you need. Note, however, that keeping

all these operations open in the History takes away from the performance abilities of

your computer. If you have set your History to 99 operations and feel that your

computer is not working properly, bring it back down to 20 for a more efficient

performance.

HUE / SATURATION

The Hue and Saturation tools in Photoshop let you be in control of certain tones

within the image, without affecting the overall balance of the image. Imagine, for

example, that you have an image of people where everything in the image seems to

be in balance, but the faces appear a bit too red. Instead of selecting the faces, or

reducing the ‘contrast’ of the whole image, you can go to

‘Image>Adjustments>Hue/Saturation’. You will get the following window:

From the drop down menu (where it says ‘Master’) choose the actual colour you

would like to change:

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In the case of the ‘red faces’ you can choose ‘Red’. Drag the ‘Saturation’ slider to the

left, and the faces will begin to look much more natural.

MORE

Photoshop has many many more features to offer, from Contrast balance to Blur

effects, from painting and erasing tools to saving options for web-optimised files.

This tutorial is intended to give you an introduction to what Photoshop can do for

you, and the initial guidelines to make its use efficient.

Wassim Jabi, Ph.D. is a Senior Lecturer at the Welsh School of Architecture

Sergio Pineda, AADip is an Architect and a Professional Tutor at the Welsh School of Architecture