mirror of
https://github.com/willnorris/imageproxy.git
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85 lines
2.6 KiB
Go
85 lines
2.6 KiB
Go
// Copyright 2013 Daniel Pupius. All rights reserved.
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// Copyright 2015 Google. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package gifresize resizes animated gifs.
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//
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// Frames in an animated gif aren't necessarily the same size, subsequent
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// frames are overlayed on previous frames. Therefore, resizing the frames
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// individually may cause problems due to aliasing of transparent pixels. This
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// package tries to avoid this by building frames from all previous frames and
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// resizing the frames as RGB.
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package gifresize // import "willnorris.com/go/gifresize"
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import (
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"image"
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"image/color"
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"image/draw"
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"image/gif"
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"io"
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)
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// TransformFunc is a function that transforms an image.
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type TransformFunc func(image.Image) image.Image
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// Process the GIF read from r, applying transform to each frame, and writing
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// the result to w.
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func Process(w io.Writer, r io.Reader, transform TransformFunc) error {
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if transform == nil {
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_, err := io.Copy(w, r)
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return err
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}
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// Decode the original gif.
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im, err := gif.DecodeAll(r)
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if err != nil {
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return err
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}
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// Create a new RGBA image to hold the incremental frames.
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firstFrame := im.Image[0].Bounds()
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b := image.Rect(0, 0, firstFrame.Dx(), firstFrame.Dy())
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img := image.NewRGBA(b)
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// Resize each frame.
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for index, frame := range im.Image {
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bounds := frame.Bounds()
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previous := img
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draw.Draw(img, bounds, frame, bounds.Min, draw.Over)
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im.Image[index] = imageToPaletted(transform(img), frame.Palette)
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switch im.Disposal[index] {
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case gif.DisposalBackground:
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// I'm just assuming that the gif package will apply the appropriate
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// background here, since there doesn't seem to be an easy way to
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// access the global color table
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img = image.NewRGBA(b)
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case gif.DisposalPrevious:
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img = previous
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}
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}
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// Set image.Config to new height and width
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im.Config.Width = im.Image[0].Bounds().Max.X
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im.Config.Height = im.Image[0].Bounds().Max.Y
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return gif.EncodeAll(w, im)
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}
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func imageToPaletted(img image.Image, p color.Palette) *image.Paletted {
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b := img.Bounds()
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pm := image.NewPaletted(b, p)
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draw.FloydSteinberg.Draw(pm, b, img, image.ZP)
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return pm
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}
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