Bitmap: definition and use in 3D rendering

A bitmap (or raster image) is an image made up of a grid of pixels, where each pixel stores a colour value. Photographs, screenshots and the final images of a 3D render are bitmaps. In architectural visualisation, bitmaps also serve a second purpose: they are the textures that describe the surface of each material within the scene.

Pixels and resolution

The pixel is the smallest unit of a bitmap. Resolution indicates how many pixels the image has in width and height, for example 3840 × 2160 pixels, which on screen is known as 4K. The more pixels, the more detail the image can contain and the more it can be enlarged or printed without the grid becoming noticeable.

It is worth distinguishing between two concepts that are often confused:

In practice: Render Fabrik is a 3D architectural rendering studio working with clients in Brazil and Europe, with a quote within 24 hours.

• Pixel resolution: the actual file size, which determines the available detail.
• Density (ppi or dpi): how many pixels are placed in each inch when printing. It is an output value; it does not add detail by itself.

When enlarging a bitmap beyond its resolution, the software has to invent intermediate pixels and the image loses sharpness. That is why a render's resolution is defined before starting the calculation, depending on its use: web, social media, printed catalogue or large-format banner.

Colour depth

Each pixel stores its colour with a certain number of bits per channel. An 8-bit-per-channel image is enough for on-screen display. 16-bit or floating-point (32-bit) images store much more light and colour information, allowing you to adjust exposure, contrast and white balance in post-production without banding or blown-out areas appearing.

Common formats

• JPG: lossy compression, lightweight files. Ideal for web and social media delivery, but not well suited to repeated editing.
• PNG: lossless compression and alpha channel (transparency). Useful for cut-outs, logos and plans with a transparent background.
• TIFF: lossless, supports 16-bit and layers. Standard format for printing and high-quality archiving.
• EXR (OpenEXR): floating-point, supports multiple channels in a single file. It is the standard for saving the raw render together with its passes (reflections, lighting, masks, depth) before post-production.
• HDR (Radiance): high dynamic range. Used mainly as an environment map: a panoramic photograph that lights the scene with the real light of a sky or an interior.

Bitmap versus vector image

A vector image is not made of pixels but of mathematically described shapes: lines, curves and fills. That is why it can be scaled without limits and without losing quality. CAD drawings, logos and typefaces are vector-based.

A bitmap, on the other hand, has a fixed resolution, but it can represent what a vector cannot represent well: complex gradients, light, soft shadows, reflections, textures and all the nuance of a photograph. In an architectural project both are used: the vector drawing serves as the basis for modelling, and the final render is always a bitmap.

Textures and maps in a 3D material

In the render engine, a material is not just a colour. It is built with several bitmaps, each controlling a physical property of the surface. This is known as the PBR (physically based rendering) workflow.

• Diffuse or base colour map (albedo): the colour and pattern of the material without light or shadows, for example the grain of wood or the tiling of porcelain stoneware.
• Normal map: an image with blue and purple tones that simulates fine relief, such as joints, pores or the roughness of a plaster finish, without adding geometry.
• Roughness map: in greyscale, it indicates which areas are matte and which are polished. It controls the appearance of reflections.
• Displacement map: also in greyscale, actually deforms the geometry. It is reserved for relief visible up close, such as natural stone, cobblestones or exposed brick.
• Other maps: metalness, ambient occlusion, opacity (for foliage or lattices) and emission (for light fixtures).

The quality of these maps largely determines the realism. A low-resolution texture looks blurry in a close-up; a texture that repeats too much reveals an artificial pattern on a large facade. Studios work with libraries of scanned materials and, when the project requires it, create textures from real manufacturer samples.

How it is used in an architectural render

In an architectural render, the bitmap appears at three stages of the process:

• Input: material textures, HDR maps for lighting, photographs of the site to integrate the building into its real environment.
• Calculation: the engine generates the image pixel by pixel, usually in EXR, with separate passes to adjust each light component.
• Output: after post-production, the image is exported in the appropriate format and resolution for each use, from lightweight JPG for web to high-resolution TIFF for printing.

If you are working on a residential or development project in Spain, you can see how we apply this workflow on our renders in Madrid page and in the section dedicated to Spain. For examples of finishes and materials in final images, see the portfolio.

Frequently asked questions

What resolution does a render need for printing?

It depends on the print size and the distance from which it will be viewed. A catalogue that is read up close requires more pixels per centimetre than a billboard seen from several metres away. The right approach is to define the final use before launching the render.

Can a bitmap be converted to vector?

It can be vectorised, but it only works well with simple images, such as logos or line drawings. A photorealistic render, with light and textures, loses all its nuance if converted to vectors.

Why is the render saved in EXR and not directly in JPG?

Because EXR retains all the light information in floating point and the separate passes. This way post-production can correct exposure, colour and reflections without degrading the image. The JPG is generated at the end, only for delivery.