Why this matters
Photoshop and Illustrator both produce visual output, but they operate on fundamentally different materials. Illustrator works on mathematical path descriptions that can be scaled to any size without degradation. Photoshop works on fixed grids of pixels whose quality is determined at the moment of document creation. Every decision you make in Photoshop — resolution, bit depth, layer organization, file format — is either an investment in future flexibility or a constraint you locked in at the start. Understanding the vocabulary is what lets you make those decisions consciously.
Pixel and resolution concepts
| Term | What it is |
|---|
| Pixel | The smallest individual unit of a raster image. Every Photoshop document is a grid of pixels, each assigned a color value. |
| Resolution (PPI) | Pixels per inch — the density of pixels relative to the physical output size. A 2000-pixel-wide image printed at 200 PPI produces a 10" wide print. The same image at 100 PPI produces a 20" wide print. Pixel count is fixed; PPI and physical size are inversely related. |
| Raster image | An image composed of a fixed pixel grid. Enlarging a raster image beyond its native resolution produces visible pixelation — the pixels become individually visible as squares. This is why document resolution must be planned for the intended output size. |
| Bit depth | The number of values each color channel can hold. 8-bit per channel = 256 tonal values; 16-bit = 65,536. 8-bit is standard for design output. 16-bit offers more headroom for heavy color correction but doubles file size and is not needed for typical LA117 deliverables. |
| Color mode | RGB (red, green, blue) for screen display and digital output. CMYK (cyan, magenta, yellow, black) for commercial print. Set to RGB for this course — digital presentation and large-format inkjet printers both use RGB. |
| Color profile | A description of the specific color space the document uses. sRGB IEC61966-2.1 is the standard for screen-displayed and web-shared images. Embedding the profile ensures consistent color across different screens and applications. |
Layer types
| Type | What it holds |
|---|
| Pixel layer | Standard raster content — painted pixels, placed images, filled areas. The default layer type. |
| Smart Object | A container that embeds or links source content (image, vector, another PSD) non-destructively. Scaling, transforming, and some filters applied to a smart object are non-destructive — the source data is preserved regardless of edits. See Card 06. |
| Adjustment layer | A non-destructive correction layer — Curves, Hue/Saturation, Color Balance, etc. — that affects all layers below it within its scope. No pixels are modified; the adjustment is calculated on output. Can be masked to affect specific areas only. |
| Fill layer | A non-destructive solid color, gradient, or pattern fill that covers its layer area. Maskable like any adjustment layer. |
| Layer group (folder) | A container for organizing related layers. Groups can be nested. Blend modes and opacity applied to a group affect all layers inside it as a unit. |
| Layer mask | A greyscale channel attached to a layer that controls where the layer is visible. White = fully visible, black = fully hidden, grey = partially transparent. Non-destructive — the pixels under the mask are always preserved. See Card 10. |
| Clipping mask | A layer clipped to the shape of the layer beneath it — content is visible only where the lower layer has pixels. Used for applying textures within filled areas. See Card 10. |
Key blend modes
| Blend mode | What it does | Primary use in LA117 |
|---|
| Normal | Layer fully covers what's below at 100% opacity | Standard placement |
| Multiply | Darkens — multiplies layer color with colors below. White becomes transparent. | Shadow overlays, adding depth to materials, darkening overlapping areas |
| Screen | Lightens — inverse of Multiply. Black becomes transparent. | Highlight overlays, adding glow or atmospheric light |
| Overlay | Combines Multiply and Screen — dark areas darken, light areas lighten, midtones are less affected | Shadow and highlight overlay layers instead of Dodge/Burn tools |
| Soft Light | Gentler version of Overlay — more subtle tonal shifts | Subtle lighting adjustments, atmosphere |
| Luminosity | Applies the luminance of the layer without changing the color of layers below | Color grading without changing tonal structure |
| Color | Applies the hue and saturation of the layer without changing the luminance below | Color tinting without changing brightness |