Library and demo app by rovertrack · Pull Request #6 · commons-app/ajpegtran

rovertrack · 2026-05-30T15:09:33Z

library module :

Jpegtran which has its own copy of the CPP source files so no naming conflicts occurs.
simplified the API, the consumer just call the required features such as Crop, Blur, Rotate no need to pass in CMD commands.
added support for multiple blur regions, which is nothing but multiple pixelize commands firing sequentially.
at present only supports get_properties, Crop, Rotate, Blur.
every feature runs in background thread.

Demo app:

added Crop and blur overlay view for the feature demonstration purpose.
bluroverlayview has mutli region support and added functionality for deleting the selected regions through bounding boxes.
save function has been updated to save the latest edited file.
Crop, Rotate, Blur fully functional.
added pinch to zoom support for blur feature.

Demo:

az_recorder_20260529_020800.mp4

Copilot

Pull request overview

Introduces a reusable jpegtran Android library that wraps the existing native jpegtran code behind a high-level Java API (getProperties, rotate, crop, blur) and adds a new commons-jpegtran-demo app that exercises that API with interactive crop/blur overlays and pinch-to-zoom. Build tooling (AGP 8.6.0, Gradle 8.7) and per-module SDK levels are also updated to support the new modules.

Changes:

New jpegtran library module: Jpegtran wrapper class, BlurRegion, RotationDegree, Properties, dedicated CPP copy with fr_free_nrw_commons_jpegtran_Jpegtran_* JNI names, multi-region pixelize support.
New commons-jpegtran-demo app with MainActivity, BlurOverlayView, CropOverlayView, plus resources/manifest, depending on :jpegtran.
Build upgrades: AGP 7.1.3 → 8.6.0, Gradle 7.2 → 8.7, library compileSdk 35 / minSdk 26, app namespace added, IDE files updated.

Reviewed changes

Copilot reviewed 26 out of 45 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
settings.gradle	Includes the new `commons-jpegtran-demo` module.
build.gradle	Upgrades AGP plugin to 8.6.0.
gradle/wrapper/gradle-wrapper.properties	Upgrades Gradle wrapper to 8.7 with SHA-256.
jpegtran/build.gradle	Library config: compile/min SDK bumps, ndkBuild path, NDK version.
jpegtran/src/main/java/.../Jpegtran.java	High-level API: getProperties/rotate/crop/blur, background executor, sequential pixelize.
jpegtran/src/main/java/.../BlurRegion.java	Immutable blur region data class and option-string serializer.
jpegtran/src/main/java/.../RotationDegree.java	Enum of allowed rotations (90/180/270).
jpegtran/src/main/java/.../Properties.java	Public JPEG properties container returned by `getProperties`.
commons-jpegtran-demo/build.gradle	New demo app module configuration.
commons-jpegtran-demo/src/main/AndroidManifest.xml	Demo app manifest.
commons-jpegtran-demo/src/main/java/.../MainActivity.java	Demo flows for open/save/crop/rotate/blur using the library.
commons-jpegtran-demo/src/main/java/.../BlurOverlayView.java	Overlay with pinch zoom, multi-region draw, delete-X handles, region mapping.
commons-jpegtran-demo/src/main/java/.../CropOverlayView.java	Resizable crop overlay with handles, grid, and gesture exclusion.
commons-jpegtran-demo/src/main/res/*	Layouts, themes, strings, colors, launcher icons.
commons-jpegtran-demo/src/{test,androidTest}/.../Example*.java	Template-generated unit/instrumented tests.
app/build.gradle	Adds required namespace; bumps buildToolsVersion.
.gitignore	Replaces blanket `.idea` ignore with selective ignores.
.idea/*	IDE configuration updates (JDK 17, deployment selector, etc.).

Files not reviewed (7)

.idea/appInsightsSettings.xml: Language not supported
.idea/compiler.xml: Language not supported
.idea/deploymentTargetSelector.xml: Language not supported
.idea/deviceManager.xml: Language not supported
.idea/gradle.xml: Language not supported
.idea/misc.xml: Language not supported
.idea/vcs.xml: Language not supported

Comments suppressed due to low confidence (1)

jpegtran/build.gradle:41

Several library classes import org.jspecify.annotations.NonNull / Nullable (here, Jpegtran.java, BlurRegion.java, and the overlay views) but neither jpegtran/build.gradle nor commons-jpegtran-demo/build.gradle declares an explicit org.jspecify:jspecify dependency. Compilation currently relies on it being pulled in transitively (e.g. by AppCompat's androidx.annotation); if that ever changes the build will break. The existing app module uses androidx.annotation.NonNull consistently — consider standardizing on AndroidX annotations or adding implementation 'org.jspecify:jspecify:<version>' to both modules' dependencies.

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+                                jpegtran.getProperties(lloadUri, p -> {
+                                    // Display properties
+                                    TextView textView = (TextView) findViewById(R.id.text_view);
+                                    propertyStr = "File name : " + p.fileName + "\n";
+                                    propertyStr += "File size : " + p.fileSize + "\n";
+                                    propertyStr += "Width : " + p.width + "\n" + "Height : " + p.height + "\n";
+                                    propertyStr += "MCU Width : " + p.MCU_Width + "\n" + "MCU Height : " + p.MCU_Height + "\n";
+                                    propertyStr += "Color space : " + p.Color_space + "\n";
+                                    textView.setText(propertyStr);
+
+                                });


+                    final Cursor returnCursor = resolver.query(fileUri, null, null, null, null);
+                    final String filename;
+                    final long filesize;
+
+                    if (returnCursor != null) {
+                        int index = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
+                        returnCursor.moveToFirst();
+                        filename = returnCursor.getString(index);
+                        index = returnCursor.getColumnIndex(OpenableColumns.SIZE);
+                        filesize = returnCursor.getLong(index);
+                        returnCursor.close();
+                    } else {
+                        filename = null;
+                        filesize = 0;
+                    }


+                    final int component_num = retarray[2];
+                    final int mcu_width = retarray[3] * 8;
+                    final int mcu_height = retarray[4] * 8;
+                    final String[] color_space_str = {"Unknown", "Grayscale", "RGB", "YCbCr", "CMYK", "YCbCrK", "RGB", "YCbCr"};


+  <string name="button_">Flip</string>
+  <string name="button_rotate">Rotate</string>
+  <string name="button_blur">blur</string>


+    public int MCU_Width;
+    /**
+     * Height of one MCU block of the JPEG,
+     *
+     */
+    public int MCU_Height;
+    /**
+     * Color space of the JPEG
+     * <p>
+     * Unknown, Grayscale, RGB, YCbCr, CMYK, YCbCrK, RGB, YCbCr.
+     *
+     */
+    public String Color_space;


+    public List<RectF> getDrawnRegions() {
+        return regions;
+    }


+        invalidate();
+    }
+
+    protected List<BlurRegion> getMappedBlurRegions(ImageView imageView, BlurOverlayView overlayView) {


+                    if (p != null) {
+                        Bitmap bitmap = BitmapFactory.decodeFile(p.getAbsolutePath());
+                        runOnUiThread(() -> {


+    static Uri loadUri = null;
+    static String propertyStr = null;


+                                    try {
+                                        // Workaround : To update mediastore, execute empty write.
+                                        OutputStream outstream = resolver.openOutputStream(saveUri, "wa");
+                                        outstream.flush();
+                                        outstream.close();
+                                    } catch (IOException e) {
+                                        // Discard exception
+                                        //  Mediastore may not be updated, but no recovery operation and continuable.
+                                    }


RitikaPahwa4444

Great start! The API mostly looks good. Had a few questions and suggestions, do share your thoughts on them :)

RitikaPahwa4444 · 2026-05-30T15:25:37Z

 }

 android {
+    namespace 'github.kamemak.ajpegtran_example'


Namespace could be modified, right?

RitikaPahwa4444 · 2026-05-30T15:32:01Z

+                                     FileInputStream fis = new FileInputStream(rparcelFd.getFileDescriptor());
+                                     FileOutputStream fos = new FileOutputStream(wparcelFd.getFileDescriptor())) {
+                                    // Sequentially read and write to save uri.
+                                    byte[] buf = new byte[8192];


Magic number? How would the usage look like in the Commons app?

RitikaPahwa4444 · 2026-05-31T08:19:29Z

+     * File name of the JPEG.
+     *
+     */
+    public String fileName;


Should be final?

RitikaPahwa4444 · 2026-05-31T08:27:33Z

+     * @param post    callback receiving the output file, or null on error
+     */
+    public void crop(@NonNull Uri fileUri,
+                     @NonNull Integer width, @NonNull Integer height,


int or Integer with @NonNull? This made me curious: https://stackoverflow.com/questions/57226605/is-it-better-to-annotate-integer-with-nonnull-or-use-primitive-int

RitikaPahwa4444 · 2026-05-31T08:28:54Z


    defaultConfig {
-        minSdk 21
+        minSdk 26


Let's keep this 21 only

RitikaPahwa4444 · 2026-05-31T08:30:27Z

+                    final String color_space = (retarray[5] >= 0 && retarray[5] <= JCS_BG_YCC)
+                            ? color_space_str[retarray[5]]
+                            : color_space_str[0]; // Unknown
+                    handler.post(() -> post.accept(new Properties(filename, filesize, width, height, mcu_width, mcu_height, color_space)));


We're not tracking component_num, is that not useful for us? We can remove it then.

RitikaPahwa4444 · 2026-05-31T08:44:23Z

+                Log.d(TAG, "pixelize error: " + e.getMessage());
+                if (tempA != null) tempA.delete();
+                if (tempB != null) tempB.delete();
+                handler.post(() -> post.accept(null));


Our callback hides the failure message from the consumer and just makes the happy path visible, is that intended? I am comparing a generic toast with displaying what exactly went wrong (consumer can decide here if the message is too technical) - the second callback would have both onSuccess() and onFailure().

RitikaPahwa4444 · 2026-05-31T08:57:18Z

+                final File finalTempFile = tempFile;
+                handler.post(() -> post.accept(finalTempFile));
+            } else {
+                tempFile.delete();


The library handles deletion of temp files on failures. Let's say I call rotate() thrice and all of them succeed. What would be the clean-up process here?

RitikaPahwa4444 · 2026-05-31T09:17:54Z

+import java.util.concurrent.Executors;
+import java.util.function.Consumer;
+
+public class Jpegtran {


What's the responsibility of this class? I feel it's handling a lot of things. Can this be split into subclasses? How about having an interface that the consumer would interact with, and this class implementing that interface?

nicolas-raoul · 2026-06-04T09:19:13Z

Please make file gradlew executable.

I had to modify this:

diff --git a/app/build.gradle b/app/build.gradle
index b86578d..b463455 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -8,7 +8,7 @@ android {
 
     defaultConfig {
         applicationId "github.kamemak.ajpegtran_example"
-        minSdk 19
+        minSdk 21
         targetSdk 31
         versionCode 1
         versionName "1.0"
@@ -42,7 +42,7 @@ android {
             path "src/main/cpp/Android.mk"
         }
     }
-    ndkVersion '21.4.7075529'
+    ndkVersion '29.0.13599879'
     buildToolsVersion '34.0.0'
 }

nicolas-raoul · 2026-06-04T09:26:41Z

+                       @NonNull Consumer<File> post) {
+
+        // Build options from params.
+        String options = "-rotate " + rotation.getDegrees() + " -optimize -copy all";


So we are basically calling the library's command-line-like interface?

Is there not a direct interface that we could call? That would be better for type-checking and could allow us to drop the command-line parsing code (this could be kept as a later improvement task though).

Yeah, that's how it works in the author's ajpegtran as well!
Under the hood it's passing the argument to CLI!

But I guess there is a function call behind the CLI, right?

So you are saying modify the native C to take params instead of CLI options?

Under the hood, matching -rotate calls select_transform(JXFORM_ROT_90) etc.

The idea would be to directly call select_transform rather than using the CLI interface. I believe that would be cleaner.

@RitikaPahwa4444 Any opinion on this?

but that means we must expose that function too right!?

Yes.
And all of the CLI-related code could be deleted.

Ok works for me if it makes the best for library :)
but Iwill also wait for one approval from @RitikaPahwa4444.

Yes, sounds good to me.

ok thanks Ritika

nicolas-raoul · 2026-06-04T09:30:32Z

+                Uri tempBUri = Uri.fromFile(tempB);
+
+                // apply blur sequentially for each region in the list.
+                for (int i = 0; i < regions.size(); i++) {


Is there no way to perform several regions pixelizations in the same JNI call? On low-end devices blurring many regions might take time if we read/write the picture once per region.

As far as I have tested it can take upto 3-4 at a time in the CLI version, even if we passed it ir modify the underlying C source, then too it is applied sequentially!

If less JNI call is priority, we can make the native C do the heavylifting!

nicolas-raoul · 2026-06-04T11:38:23Z

The blur is perfect, other blocks untouched.

rovertrack · 2026-06-04T11:49:34Z

The blur is perfect, other blocks untouched.

Is there any particular image tester you are using?
Did you test it with the demo app?
Still i think it kind of gets big like 1px when applied I think it is automatically snapping to nearest block edge!

nicolas-raoul · 2026-06-04T14:24:17Z

rovertrack · 2026-06-04T14:31:33Z

Thanks Nicolas :)

nicolas-raoul · 2026-06-08T08:54:42Z

Somehow in this PR's jpegtran app when I click "Open" and select a picture, the metadata is shown but nothing else.
The strange thing is that it was working a few days agao, when I posted the result screenshot above, and I did not reinstall since then... any idea what could be wrong?

rovertrack · 2026-06-08T08:57:34Z

Somehow in this PR's jpegtran app when I click "Open" and select a picture, the metadata is shown but nothing else. The strange thing is that it was working a few days agao, when I posted the result screenshot above, and I did not reinstall since then... any idea what could be wrong?

Is it the upstream app or the one which was created to test out library. The details you are describing is of the app which was upstream kamemak authored! Which only opens, shows metadata and saves with hardcoded options.

nicolas-raoul · 2026-06-08T09:02:20Z

Ah thanks Rishan, very useful, I was using the wrong app indeed! I will uninstall the upstream app.

rovertrack · 2026-06-08T09:10:26Z

Was pretty sure that was what happened 👍

rovertrack · 2026-06-08T09:11:25Z

Also it's ok if you dont test this much, this week I'm gonna be restructuring based on you recommendation of exposing methods per feature!

nicolas-raoul · 2026-06-08T10:11:37Z

Rotation and crop also work well:

The above UI is https://github.com/nicolas-raoul/jpeg_diff_android

rovertrack added 3 commits May 30, 2026 20:07

demo module

088dade

library module

0b568f4

update version files

b953c92

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rovertrack closed this Jun 17, 2026

rovertrack deleted the dev2 branch June 25, 2026 19:15

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