Ensure TIFF is cast when using float predictor (#2502)

docs/changelog.md

@@ -6,6 +6,10 @@ Requires libvips v8.10.5
 
 ### v0.27.1 - TBD
 
+* Ensure TIFF is cast when using float predictor.
+  [#2502](https://github.com/lovell/sharp/pull/2502)
+  [@randyridge](https://github.com/randyridge)
+
 * Add support for Uint8Array and Uint8ClampedArray input.
   [#2511](https://github.com/lovell/sharp/pull/2511)
   [@leon](https://github.com/leon)

src/pipeline.cc

@@ -955,6 +955,10 @@ class PipelineWorker : public Napi::AsyncWorker {
             sharp::AssertImageTypeDimensions(image, sharp::ImageType::JPEG);
             baton->channels = std::min(baton->channels, 3);
           }
+          // Cast pixel values to float, if required
+          if (baton->tiffPredictor == VIPS_FOREIGN_TIFF_PREDICTOR_FLOAT) {
+            image = image.cast(VIPS_FORMAT_FLOAT);
+          }
           image.tiffsave(const_cast<char*>(baton->fileOut.data()), VImage::option()
             ->set("strip", !baton->withMetadata)
             ->set("Q", baton->tiffQuality)

test/unit/tiff.js

@@ -277,7 +277,7 @@ describe('TIFF', function () {
       });
   });
 
-  it('TIFF deflate compression with float predictor shrinks test file', function (done) {
+  it('TIFF deflate compression of integral input with float predictor increases file size', function (done) {
     const startSize = fs.statSync(fixtures.inputTiffUncompressed).size;
     sharp(fixtures.inputTiffUncompressed)
       .tiff({
@@ -287,7 +287,7 @@ describe('TIFF', function () {
       .toFile(fixtures.outputTiff, (err, info) => {
         if (err) throw err;
         assert.strictEqual('tiff', info.format);
-        assert(info.size < startSize);
+        assert(info.size > startSize);
         rimraf(fixtures.outputTiff, done);
       });
   });