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Add named 'alpha' channel to extractChannel op #2138

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Lovell Fuller
2020-06-07 10:43:27 +01:00
parent 7f142bddb3
commit 17ea70a102
6 changed files with 28 additions and 11 deletions
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13
lib/channel.js
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@@ -60,22 +60,19 @@ function ensureAlpha () {
* // green.jpg is a greyscale image containing the green channel of the input
* });
*
* @param {number|string} channel - zero-indexed band number to extract, or `red`, `green` or `blue` as alternative to `0`, `1` or `2` respectively.
* @param {number|string} channel - zero-indexed channel/band number to extract, or `red`, `green`, `blue` or `alpha`.
* @returns {Sharp}
* @throws {Error} Invalid channel
*/
function extractChannel (channel) {
if (channel === 'red') {
channel = 0;
} else if (channel === 'green') {
channel = 1;
} else if (channel === 'blue') {
channel = 2;
const channelMap = { red: 0, green: 1, blue: 2, alpha: 3 };
if (Object.keys(channelMap).includes(channel)) {
channel = channelMap[channel];
}
if (is.integer(channel) && is.inRange(channel, 0, 4)) {
this.options.extractChannel = channel;
} else {
throw is.invalidParameterError('channel', 'integer or one of: red, green, blue', channel);
throw is.invalidParameterError('channel', 'integer or one of: red, green, blue, alpha', channel);
}
return this;
}