Photoshop: File Types

Photoshop can read and write several image file types, each of which is appropriate for different purposes.

JPEG: General purpose; allows for variable levels of file compression at the increasing expense of image quality. (A “lossy” file format.)

TIFF: A good archival file format. Supports layers. Allows for file compression using the LZW method (a “lossless” method).

PSD: Photoshop’s native file format. Supports layers, vector and shape information, text.

GIF: Works only with limited color palettes; appropriate for use on websites.

PDF: Useful if you’re sending information to someone who doesn’t have Photoshop.


Techniques for Reducing File Size

This page summarizes file-size reduction techniques for several software applications. File-size reduction strategies are usually directed toward managing the overall size of a package of documents.

NOTE: As a general rule, full-size (non-reduced) copies of important documents should always be archived and backed up: reduced-size copies are not usually meant as a replacement for full versions.


MANAGING LAYERS. A reduced-size Photoshop image, regardless of file type, should always be “flattened” into a single layer. Use the Layer > Flatten Image command.

MANAGING IMAGE RESOLUTION. Use the Image > Image Size command to adjust image dimensions and resolution. Images measuring approximately 5” or 6” in their longest dimension, with a resolution of 150 or 200 pixels per inch, usually represent a good balance between file size and image quality.

CHOOSING THE PROPER FILE TYPE. Generally, though not always, the smallest Photoshop files will be met by using the JPEG file type. Use the File > Save As command. Setting the JPEG quality to “Medium” will represent a good balance of size and quality. In the case of images with large areas of solid color, using the TIFF format (with LZW compression) will usually result in a smaller file.


CHOOSING THE PROPER FILE TYPE. Illustrator uses two different “native” file formats, AI and PDF. To reduce file size, use the File > Save As command to save your Illustrator file in PDF format. When prompted to choose an “Adobe PDF Preset,” choose “Smallest File Size.”

ADDITIONAL OPTIONS. Refer to this site for a detailed description of Illustrator optimization techniques:


COMBINING DOCUMENTS IN ADOBE ACROBAT. If you choose to combine files into a single PDF, click the “Smallest File Size” icon. Use the “Single PDF” rather than the “PDF Portfolio” option.

PRINTING AS THE SMALLEST FILE SIZE. Open a PDF in Acrobat. Choose File > Print. Select PDF as your printer (Adobe PDF or a PDF Writer). Click the “Properties” button. Under “Default Settings,” choose “Smallest File Size.” Click OK, and then click Print.


PURGING THE AUTOCAD DRAWING. AutoCAD drawings often contain unnecessary information (e. g., unused blocks, layers, text styles, etc.). Type PURGE at the command prompt to eliminate such information. Follow the PURGE command with the File > Save As command.

THE OVERKILL COMMAND. Type OVERKILL at the command prompt to delete certain kinds of information in the drawing, e. g., lines which overlap other lines.

FILE > SAVE AS. Use this command to save a new copy of your AutoCAD file. This will usually reduce file size.


PURGING UNUSED ITEMS. Under the Manage tab, Settings panel, choose Purge Unused. This tool will tend to have a greater effect on Projects than Families.

[APPLICATION MENU] > SAVE AS. Use this command to save a new copy of your Revit file. This will usually reduce file size. Test the effect of checking the “Compact File” option while saving (Click Options in the Save As dialog box).


PURGE THE MODEL. Type PURGE at Rhino’s command prompt.

FILE > SAVE AS. Use this command to save a new copy of your Rhino file. This will usually reduce file size.


PURGE UNUSED. Choose Window > Model Info > Statistics; click Purge Unused. Follow this with File > Save As.

ELIMINATE TEXTURES. A copy of your model saved without textures will be much smaller than the same model with textures.

FILE > SAVE AS. Use this command to save a new copy of your SketchUp file. This will usually reduce file size.



Photoshop: Selection

Photoshop allows you to define areas upon which you will apply a tool or command. The act of defining such an area is called selection. The simplest selection tool is the marquee, or rectangular selection tool.


1.  Select the Rectangular Marquee Tool (upper-left-hand corner of the tools palette).

2.  Drag the mouse within the image to draw a rectangular area.

3.  Apply one of the Image > Adjust tools (such as Image > Adjust > Color Balance) to see its effect.

4.  Choose Select > None to clear the selection boundary.


The lasso tool makes freely curved selections and the polygonal lasso makes polygonal selections.


The magic wand tool selects adjacent pixels with similar levels of brightness. In the options palette (along the top of the screen), you can set the tolerance of the wand, from 0 (highly discriminating) to 255 (does not discriminate between different values).

Using the magic wand tool:

1.  Choose the magic wand tool from the toolbar. In the options palette, set the tolerance to 30 or 40.

2.  Click within an area of solid color in your image.

3.  Apply one of the Image > Adjust tools to see its effect.

4.  Choose Deselect from the Select menu and then repeat the above steps with different values for tolerance.


Select > All  selects the entire image.

Select > Deselect  deselects everything.

Select > Reselect reselects the last selection.

Select > Inverse selects any deselected areas while unselecting any selected areas.

Select > Color Range produces similar results as the Magic Wand followed by Select > Similar, although Color Range gives a greater degree of control.

Select > Modify > Border selects a border of specified width along the current selection boundary.

Select > Modify > Feather makes the selection edges soft rather than sharp.

Select > Grow enlarges any selection(s) to include adjacent areas with similar colors.

Select > Similar selects pixels similar in brightness to the currently selected pixels.

Select > Transform Selection allows you to stretch, distort, or rotate a selection boundary.


Use the Move tool (upper right-hand corner of the Tools palette) to move or copy selected areas. To move selected pixels, choose the move tool and drag the selection with the mouse. To copy, hold Alt while dragging the selection. Hold the Shift key down to constrain the movement of the mouse to horizontal, vertical, or 45 degree motion.


Options under Edit > Transform are useful for scaling, rotating, or otherwise transforming selected pixels. To accept a transformation, press Enter.

To distort a rectangular selection:

1. Use the marquee tool to select a rectangular area.

2. Choose Edit > Transform > Distort. You will see “handles” appear at the corners and sides of the selected area.

3. Use the mouse to move one or more of the corner handles. The selected area will distort to the modified boundary. Press Enter to complete the action.


Once a selection is defined, it can be saved for later use. (Note that what is being saved is not the content of the selected area, but the shape and quality of the selection border.)

Selections are saved in Channels. Channels are simply grayscale images that correspond to the overall shape of your Photoshop image. The level of gray in a channel corresponds to the “amount” of selection – completely black areas are 100% unselected, and completely white areas are 100% selected.

Photoshop: Layers

Photoshop images can be composed of more than one layer. Layers are like sheets of transparent film on which pixels are painted. Layers may be edited separately and individual layers can be made visible or invisible. Layers can be rearranged; their opacity may be changed; their blending mode can be altered, providing different overlay effects. Be aware that each new layer adds a significant amount of information to your file size.

Once selected, a group of pixels can be copied and pasted within its original image or into a new one. The act of pasting creates a new layer (see Windows > Layers).

A multi-layered image can be flattened to save file space and reduce printing time, but the flattened layers cannot be separated. For this reason, it’s good practice to choose File > Save As before flattening layers in a Photoshop image.


Make a layer current by clicking its name in the Layers palette. Any actions you perform will (in general) affect only the current layer.

Click on the eye symbol in the Layers palette to make a layer invisible or visible.

Change the opacity of the current layer by sliding the bar at the top of the palette. (Note: you cannot change the opacity of the Background layer.)

Change the display order of layers by dragging them up and down on the list.


Normal assumes that the top layer is opaque, unless adjusted by some other means (e. g., the Opacity setting in the Layers palette).

Multiply treats white pixels in the top layer as transparent. 50% white pixels are treated as 50% transparent, and so on.

Screen is exactly the opposite of Multiply. Black pixels in the top layer are treated as transparent.

Overlay combines the effects of Multiply and Screen. 50% (gray) pixels in the top layer are treated as completely transparent. Dark pixels become darker and light pixels become lighter.


To add a new layer: In the Layers palette, choose Layer > New Layer and give it a name. By default, new layers are totally transparent in Photoshop until you paste something onto them or paint on them.

To combine layers: In the Layers palette, choose Layer > Merge Visible to combine the visible layers onto the current layer.

To make the entire image into a single layer: In the Layers palette, choose Layer > Flatten Image.


1.  Activate the layer you want to copy from and make the selection. Choose Edit > Copy.

2.  Activate the layer onto which you want to paste the selection. Choose Edit > Paste. Photoshop will automatically create a new layer above the current layer.

3.  (Optional.) Click on the new layer in the Layers palette and choose Layer > Merge Down. (This combines the new layer with the layer immediately below.).



Photoshop: Image Resolution

Every Photoshop image is rectangular in shape, corresponding to a fixed measurable size (in inches), and exists at a fixed resolution (usually expressed in pixels per inch).

72 pixels per inch is appropriate for on-screen display (e. g., websites).

300 pixels per inch is appropriate for printed photographs.

600 pixels per inch is appropriate for printed vector drawings and/or text.

Image resolutions greater than 600 pixels per inch might arise in the case of scanned slides.

Use Photoshop’s Image > Image Size command to change an image’s measured size and resolution.

What is Photoshop?

Photoshop is an image-editing program – its images are composed of a grid of pixels and closely approximate continuous-tone photographs. Photoshop provides tools and commands used to edit images on a pixel-by-pixel basis.

In general, most operations in Photoshop are of the following form:

1.  Use a tool or a command to select pixels within the image.

2.  Perform an action on the selected pixels to change their color.