Channels, Feature Maps & Receptive Fields
How depth builds richer features.
Channels, Feature Maps & Receptive Fields is a free Deep Learning Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Deep Learning Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Color Images Have Channels
A color photo is not one grid but three: red, green, and blue. Each is a channel, so the image has shape 3 by height by width.
Kernels Span All Channels
A conv kernel covers every input channel at once. For RGB, a 3x3 kernel is really 3x3x3 and sums across all three.
One Kernel, One Feature Map
No matter how many input channels there are, a single kernel produces just one output grid: one feature map.
Out Channels Stack Maps
A layer learns many kernels. Its out_channels count is exactly how many feature maps it stacks into the output.
conv = nn.Conv2d(3, 32, kernel_size=3, padding=1)Reading That Layer
That layer takes 3 input channels and outputs 32 feature maps. Each map is one learned kernel scanning the RGB image.
Maps Become the Next Input
The 32 feature maps feed the next conv layer as its input channels. So depth grows as layers stack on top of each other.
What Is a Receptive Field?
A receptive field is the region of the original image that influences one output value. Early layers see only a tiny patch.
It Grows With Depth
Stack more conv layers and each value depends on a wider area. Deep neurons have a large receptive field spanning much of the image. 🌐
Simple Features First
With small receptive fields, early layers detect simple things: edges, corners, and color blobs. They are the network's basic features.
Then Complex Features
Deeper layers combine those into richer patterns: textures, shapes, and eventually whole objects like an eye or a wheel. This is the feature hierarchy.
Depth Trades Space for Meaning
As you go deeper, maps usually get smaller but gain more channels. The network swaps spatial detail for semantic meaning.
Quick Check
Let us check how channels relate to feature maps.
Recap: Depth Builds Meaning
You learned that kernels span all input channels, out_channels stacks feature maps, and growing receptive fields turn edges into whole objects. 🎉
Frequently asked questions
Is the “Channels, Feature Maps & Receptive Fields” lesson free?
Yes — the full text of “Channels, Feature Maps & Receptive Fields” is free to read here on the web, and the Deep Learning Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Deep Learning Academy course, upgrade to CoddyKit PRO.
What will I learn in “Channels, Feature Maps & Receptive Fields”?
How depth builds richer features. You practise Deep Learning Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Deep Learning Academy?
No prior experience is required. Deep Learning Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Channels, Feature Maps & Receptive Fields” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Deep Learning Academy lesson?
Yes. Every Deep Learning Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Convolution: Kernels Slide Over Pixels
- Stride, Padding & Pooling
- Channels, Feature Maps & Receptive Fields
- Assemble a CNN Image Classifier