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Snap to standard formats: A4, Letter...

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This commit is contained in:
Pierre-Yves Nicolas
2026-05-23 20:10:51 +02:00
parent 9394b19731
commit c3bd144681
6 changed files with 179 additions and 10 deletions
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2
app/src/main/java/org/fairscan/app/domain/ExportPreparation.kt
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@@ -39,7 +39,7 @@ data class PageToExport(
val quad = metadata.normalizedQuad.scaledTo(1.0, 1.0, size.width, size.height)
val realDimensions = estimateRealDimensions(
quad, size.width.toInt(), size.height.toInt(), metadata.opticalMeasures
)
).snapToStandardFormat()
return realDimensions.applyRotation(metadata.baseRotation)
}
}

29
app/src/main/java/org/fairscan/app/platform/AndroidPdfWriter.kt
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@@ -24,6 +24,7 @@ import org.fairscan.app.BuildConfig
import org.fairscan.app.data.PdfWriter
import org.fairscan.app.domain.PageToExport
import org.fairscan.imageprocessing.EstimatedDimensions
import org.fairscan.imageprocessing.PaperFormats
import java.io.OutputStream
import java.util.Calendar
@@ -43,17 +44,18 @@ class AndroidPdfWriter : PdfWriter {
val heightPx = image.height.toFloat()
val dimensions = page.estimatedDimensions()
val (widthPoints, heightPoints) = when (dimensions) {
is EstimatedDimensions.Physical -> {
dimensions.widthMm.toFloat() * pointsPerMm to dimensions.heightMm.toFloat() * pointsPerMm
}
val (widthMm, heightMm) = when (dimensions) {
is EstimatedDimensions.Physical ->
clipToMaxFormat(dimensions.widthMm, dimensions.heightMm)
else -> {
// No physical dimensions available: approximate using US Letter max dimension
val maxDimInMm = 279.4f
val scalePxToMm = maxDimInMm / maxOf(widthPx, heightPx)
widthPx * scalePxToMm * pointsPerMm to heightPx * scalePxToMm * pointsPerMm
// No physical dimensions available
val maxDimMm = PaperFormats.A4.heightMm
val scalePxToMm = maxDimMm / maxOf(widthPx, heightPx)
clipToMaxFormat(widthPx * scalePxToMm, heightPx * scalePxToMm)
}
}
val widthPoints = widthMm.toFloat() * pointsPerMm
val heightPoints = heightMm.toFloat() * pointsPerMm
val page = PDPage(PDRectangle(widthPoints, heightPoints))
document.addPage(page)
@@ -68,3 +70,14 @@ class AndroidPdfWriter : PdfWriter {
return doc.numberOfPages
}
}
fun clipToMaxFormat(widthMm: Double, heightMm: Double): Pair<Double, Double> {
// Normalize to portrait for comparison
val (w, h) = if (widthMm <= heightMm) widthMm to heightMm else heightMm to widthMm
val portrait = widthMm <= heightMm
val maxFormat = PaperFormats.A4
val scale = minOf(maxFormat.widthMm / w, maxFormat.heightMm / h, 1.0)
val clipped = w * scale to h * scale
return if (portrait) clipped else clipped.second to clipped.first
}

58
app/src/test/java/org/fairscan/app/platform/AndroidPdfWriterTest.kt Normal file
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@@ -0,0 +1,58 @@
/*
* Copyright 2025-2026 The FairScan authors
*
* This program is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
* You should have received a copy of the GNU General Public License along with
* this program. If not, see <https://www.gnu.org/licenses/>.
*/
package org.fairscan.app.platform
import org.assertj.core.api.Assertions.assertThat
import org.assertj.core.api.Assertions.offset
import org.junit.Test
class AndroidPdfWriterTest {
@Test fun `portrait smaller than A4 is unchanged`() {
val (w, h) = clipToMaxFormat(100.0, 150.0)
assertThat(w).isEqualTo(100.0)
assertThat(h).isEqualTo(150.0)
}
@Test fun `portrait taller than A4 is clipped preserving ratio`() {
val (w, h) = clipToMaxFormat(210.0, 400.0)
assertThat(h).isCloseTo(297.0, offset(0.1))
assertThat(w / h).isCloseTo(210.0 / 400.0, offset(0.001))
}
@Test fun `landscape wider than A4 is clipped preserving ratio`() {
val (w, h) = clipToMaxFormat(300.0, 200.0)
assertThat(w).isCloseTo(297.0, offset(0.1))
assertThat(w / h).isCloseTo(300.0 / 200.0, offset(0.001))
}
@Test fun `exactly A4 is unchanged`() {
val (w, h) = clipToMaxFormat(210.0, 297.0)
assertThat(w).isCloseTo(210.0, offset(0.001))
assertThat(h).isCloseTo(297.0, offset(0.001))
}
@Test fun `landscape orientation is preserved after clip`() {
val (w, h) = clipToMaxFormat(400.0, 250.0)
assertThat(w).isGreaterThan(h)
}
@Test fun `landscape smaller than A4 is unchanged`() {
val (w, h) = clipToMaxFormat(297.0, 150.0)
assertThat(w).isCloseTo(297.0, offset(0.001))
assertThat(h).isCloseTo(150.0, offset(0.001))
}
}

2
imageprocessing/src/main/java/org/fairscan/imageprocessing/DocumentDetection.kt
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@@ -164,7 +164,7 @@ fun extractDocument(
inputMat.cols(),
inputMat.rows(),
opticalMeasures,
)
).snapToStandardFormat()
val (targetWidth, targetHeight) = estimatedDimensions.toPixelDimensions(quad)
val srcPoints = MatOfPoint2f(
quad.topLeft.toCv(),

35
imageprocessing/src/main/java/org/fairscan/imageprocessing/Perspective.kt
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@@ -14,6 +14,7 @@
*/
package org.fairscan.imageprocessing
import kotlin.math.abs
import kotlin.math.absoluteValue
import kotlin.math.max
import kotlin.math.sqrt
@@ -63,6 +64,40 @@ sealed class EstimatedDimensions {
is Physical -> heightMm / widthMm
is Ratio -> height / width
}
fun snapToStandardFormat(
ratioTolerance: Double = 0.04,
dimensionTolerance: Double = 0.20,
): EstimatedDimensions {
if (this !is Physical) return this
// Normalize to portrait for comparison
val (w, h) = if (widthMm <= heightMm) widthMm to heightMm
else heightMm to widthMm
val portrait = widthMm <= heightMm
for (format in PaperFormats.all) {
val (fw, fh) = format.widthMm to format.heightMm // format is always portrait
val ratioError = abs((h / w) - (fh / fw)) / (fh / fw)
val dimError = maxOf(abs(w - fw) / fw, abs(h - fh) / fh)
if (ratioError < ratioTolerance && dimError < dimensionTolerance) {
return if (portrait) format
else Physical(format.heightMm, format.widthMm)
}
}
return this
}
}
object PaperFormats {
val A3 = EstimatedDimensions.Physical(297.0, 420.0)
val A4 = EstimatedDimensions.Physical(210.0, 297.0)
val A5 = EstimatedDimensions.Physical(148.0, 210.0)
val Letter = EstimatedDimensions.Physical(215.9, 279.4)
val Legal = EstimatedDimensions.Physical(215.9, 355.6)
val all = listOf(A4, Letter, Legal, A5, A3)
}
/**

63
imageprocessing/src/test/java/org/fairscan/imageprocessing/EstimatedDimensionsTest.kt Normal file
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@@ -0,0 +1,63 @@
/*
* Copyright 2025-2026 The FairScan authors
*
* This program is free software: you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
* You should have received a copy of the GNU General Public License along with
* this program. If not, see <https://www.gnu.org/licenses/>.
*/
package org.fairscan.imageprocessing
import org.assertj.core.api.Assertions.assertThat
import org.fairscan.imageprocessing.EstimatedDimensions.Physical
import org.fairscan.imageprocessing.EstimatedDimensions.Ratio
import org.junit.Test
class EstimatedDimensionsTest {
@Test fun `ratio is returned unchanged`() {
val input = Ratio(212.0, 300.0)
assertThat(input.snapToStandardFormat()).isEqualTo(input)
}
@Test fun `A4-sized physical dims snap to exact A4`() {
val input = Physical(212.0, 300.0)
assertThat(input.snapToStandardFormat()).isEqualTo(PaperFormats.A4)
}
@Test fun `A3-sized physical dims snap to exact A3`() {
val input = Physical(297.0, 420.0)
assertThat(input.snapToStandardFormat()).isEqualTo(PaperFormats.A3)
}
@Test fun `A5-sized physical dims snap to exact A5`() {
val input = Physical(149.0, 211.0)
assertThat(input.snapToStandardFormat()).isEqualTo(PaperFormats.A5)
}
@Test fun `landscape A4 snaps to landscape A4`() {
val input = Physical(300.0, 212.0)
assertThat(input.snapToStandardFormat()).isEqualTo(Physical(297.0, 210.0))
}
@Test fun `Letter-sized dims snap to exact Letter`() {
val input = Physical(218.0, 281.0)
assertThat(input.snapToStandardFormat()).isEqualTo(PaperFormats.Letter)
}
@Test fun `dims far from any standard format are unchanged`() {
val input = Physical(150.0, 400.0)
assertThat(input.snapToStandardFormat()).isEqualTo(input)
}
@Test fun `aspect ratio`() {
assertThat(Physical(100.0, 150.0).aspectRatio).isEqualTo(1.5)
assertThat(Ratio(100.0, 150.0).aspectRatio).isEqualTo(1.5)
}
}